The Complete Pergola & Outdoor Structure Glossary
Western Timber Frame | Glossary Reference
WESTERN TIMBER FRAME
Complete Glossary
Pergola & Outdoor Structure Terminology — 235+ Terms, 17 Categories
The most comprehensive guide to outdoor structure terminology on the web — written for homeowners, not engineers.
If you’ve ever been confused by the difference between a rafter and a purlin, wondered what “checking” means on a timber, or wanted to know why your contractor keeps mentioning “dead load” — this is for you. We built this glossary from 16 years and 7,000+ projects worth of conversations with homeowners, contractors, engineers, and building departments. It covers everything from structure types to wood science to the building codes that govern what gets built and how.
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Structure Types
ADA Compliant Structures (Accessible Ramps / Accessibility Structures)
Timber-framed structures designed and engineered to meet Americans with Disabilities Act accessibility requirements — including ramps, walkways, platforms, and deck systems. Engineered to applicable slope, width, load, and handrail requirements for residential, commercial, and public applications.
Arbor
A smaller overhead structure, typically arched or flat, designed to frame an entrance, define a garden passage, or serve as a focal point for climbing plants. Arbors are narrower and shorter than pergolas and are not intended to cover a living or entertaining area. Sometimes called a garden arch.
Awning
A small overhead structure or covering that projects from a wall, post, or beam to provide shade, weather protection, and architectural definition over a window, door, entry point, or outdoor seating area. Awnings can be fixed or retractable, fabric or solid, and freestanding or building-mounted. In timber construction, awnings are typically framed with heavy timber brackets and a skillion-style roof finished to match the surrounding structure.
Breezeway
A covered, open-sided passageway connecting two structures — typically a home to a garage, guesthouse, or outbuilding. Timber breezeways combine function and architectural character, creating a sheltered transition between buildings while extending the design language of the home. Engineered as an attached or freestanding structure depending on the site.
Bridge
A timber-framed span structure designed to cross a gap, gully, grade change, or body of water. Pedestrian bridges are fully engineered for load requirements and site-specific conditions regardless of whether water is present beneath the span.
Cabana
An enclosed or semi-enclosed outdoor structure typically associated with pool areas. Cabanas may have solid walls on one or more sides, curtains, or retractable screens. They function as a changing area, shade retreat, or outdoor room and can range from simple shade structures to fully finished rooms with plumbing and electrical.
Carport
A timber-framed vehicle shelter with an open or partially open design — typically a solid or open-slat roof supported by posts, without fully enclosed walls. Provides weather protection for vehicles while adding architectural presence to the home’s exterior. Can be freestanding or attached and engineered to match the timber style of the primary structure.
Deck
A flat, open-air platform structure built from timber framing and decking boards, designed for outdoor living, entertaining, and recreation. Can be built as a standalone structure, multilevel, or rooftop application and is typically custom-sized to the site and use.
Dock
A timber-framed platform structure extending over freshwater — lakes, ponds, and rivers — providing access for swimming, fishing, boating, and waterfront recreation. Engineered for specific load requirements, water depth, and shoreline conditions of each site. Species selection prioritizes moisture resistance and ground-contact durability.
Gazebo
A freestanding structure with a solid roof, open sides, and a polygonal footprint — most commonly six-sided (hexagonal) or eight-sided (octagonal). The distinctive multi-sided shape separates a gazebo from a pavilion, which is typically rectangular. Gazebos are a classic element in parks, gardens, and waterfront properties. Engineering a gazebo is more complex than a rectangular structure because every joint involves compound angles.
Growbox (Raised Garden Bed)
A custom-built timber planter structure designed for raised-bed gardening. Can be installed as a standalone garden feature or integrated into a larger landscape project. Species selection prioritizes ground-contact durability and resistance to moisture and biological degradation.
Outdoor Living Structure
A timber-framed structure designed to shelter and define an outdoor living space — accommodating any combination of uses including cooking, dining, entertaining, fire features, media systems, and relaxation. The timber structure provides the overhead coverage, architectural presence, and engineered framework; fixtures, appliances, fire features, and entertainment components are sourced and installed separately or by the client. Most WTF structures serve multiple functions simultaneously and are designed around how the homeowner actually lives outdoors rather than a single designated use.
Patio Cover
A broad term for any overhead structure — open or solid — attached to a home and extending over a patio. In many building codes, patio covers are addressed specifically under IRC Appendix AH, which governs structural requirements, setbacks, and permitting. “Patio cover” is often used interchangeably with “pergola” in contractor language, even though they can describe very different structures.
Pavilion
A freestanding structure with a solid, fully enclosed roof and open sides. Unlike a pergola, a pavilion provides complete protection from sun, rain, and snow. This distinction matters for engineering (solid roofs catch wind and shed water differently than open rafters), permitting (many jurisdictions classify solid-roof structures differently for setback requirements), and pricing (a pavilion requires roofing materials, flashing, and drainage that a pergola does not). Many homeowners use the word “pergola” when they’re actually picturing a pavilion.
Pergola
An outdoor structure with vertical posts supporting an open-roof system of beams and rafters. The open roof provides partial shade while allowing light and air to filter through. Pergolas can be freestanding or attached to the home. The word comes from the Late Latin pergula, meaning “projecting eave.” In modern use, “pergola” has become an umbrella term that homeowners apply to almost any outdoor overhead structure — which is exactly why the distinctions below matter.
Porte-Cochère
A covered structure extending from the entrance of a building over an adjacent driveway, designed to shelter passengers as they enter or exit vehicles. In residential applications, a timber porte-cochère makes a dramatic architectural statement at the home’s entry. Requires significant structural engineering due to the wide, unsupported spans needed to clear vehicle height and width.
Ramada
A freestanding structure with a solid roof and open sides, similar to a pavilion. The term is most common in the American Southwest and often refers to structures placed over outdoor kitchens, fire features, or seating areas. Some landscape professionals use “ramada” and “pavilion” interchangeably.
Solar Pergola (Solar Stand)
A timber-framed structure designed to support solar panels — either as a pergola-style overhead structure where panels replace traditional shade planks, or as a ground-mounted solar panel support frame. Can be standalone or integrated into a larger outdoor living design.
Sunroom (Timber-Framed Sunroom)
A year-round living structure built on a heavy timber frame — posts, beams, and roof framing — with glass wall systems infilled between the timber members. WTF provides the complete timber frame package; glass walls, sliding doors, and window systems are sourced and installed separately by the client or a glazing contractor.
Timber Boathouse
A timber-framed structure built over or adjacent to water to shelter and store watercraft. WTF provides the timber framing — posts, beams, roof structure, and decking — engineered for the load requirements and moisture exposure of a waterfront environment. Species selection prioritizes natural decay resistance for long-term performance in high-humidity, water-adjacent conditions.
Trellis
A freestanding or wall-mounted structure built from a vertical framework of posts and infill — lattice, crossed members, or open framing — designed to support climbing plants, define a garden space, or serve as a decorative garden feature. A trellis is a structure in its own right and should not be confused with lattice panels, which are a material/panel product used within or alongside other structures. → See also: Lattice Panels (Panels, Enclosures & Screens)
Timber Bell Tower
A freestanding timber frame structure engineered to support and display a bell at an elevated height. Common in parks, churches, schools, and civic spaces. Engineered for the point load and dynamic load requirements of a hanging bell, including the lateral forces generated by bell movement.
Timber Overlook Platform
A raised timber frame structure that extends out over a grade change, terrain feature, or landscape element — providing an elevated vantage point without spanning to a connecting surface on the far end. Common in parks, trails, civic spaces, and master-planned communities. Engineered for the specific load requirements, post depth, and site conditions of each application, including the lateral forces of an occupied cantilevered platform edge.
Timber Sign Structure / Timber Monument Sign
A large-scale timber frame engineered to support and display signage for a commercial, civic, or community property. Combines heavy timber posts and beams with steel connection hardware for structural stability and visual impact.
Veranda
A roofed, open-sided structure attached to the exterior of a home, typically wrapping along one or more sides. More common in traditional and colonial architecture. Distinguished from a porch primarily by length — verandas typically extend along the full face of a building rather than covering just an entryway.
Roof Styles & Configurations
Barrel Roof
Barrel roofs are created using curved beams or laminated timbers that form a continuous arc. This design adds architectural elegance while allowing for open, spacious interiors beneath. A barrel roof introduces a softer, more organic shape to a structure, enhancing visual appeal while efficiently distributing weight. It creates a sense of openness and craftsmanship that elevates both residential and commercial spaces.
Deck-Top Pergola
A timber frame pergola engineered to support a fully functional deck structure above the pergola roof. The pergola serves as the structural base for the elevated deck, creating two distinct outdoor living levels — a shaded, covered space below and an open-air deck above. Deck-Top Pergolas are custom-engineered to meet the combined load requirements of both the pergola and the occupied deck surface, including live loads, railing systems, and any additional features integrated into the upper level.
Crescent Roof
A proprietary Western Timber Frame roof style featuring rafters and rafter tails cut with a concave, inward-curving profile. The roofline sweeps upward at the edges in a graceful arc, creating a distinctive silhouette that reads as architectural rather than utilitarian. Every rafter tail is CNC-precision cut for an exact, continuous curve across the full length of the structure. Also referred to as: Inverted Radius Roof.
Crown Roof
A proprietary Western Timber Frame roof style featuring rafters and rafter tails cut with a convex, outward-curving profile. The roofline arcs downward and outward at the edges, creating a sweeping silhouette that evokes the curve of a crown. Every rafter tail is CNC-precision cut for an exact, continuous curve across the full length of the structure.
3rd Gable Roof
A gable roof with a third gable projecting outward from one of the long sides, creating a T-shaped roofline. Adds architectural interest, additional interior volume, and a distinctive silhouette to structures where a standard two-gable roof would feel too plain. Requires compound angle joinery where the third gable intersects the main ridge.
Cross-Gable Roof (WTF 4-Gable Roof)
A roof configuration with four gable ends formed by two intersecting ridges running perpendicular to each other, creating a plus-shaped roofline. Used for L-shaped, T-shaped, or complex footprints. Requires precise compound angle joinery at the intersection and careful engineering for proper drainage at the valley.
Flat Roof (Low-Slope Roof)
A nearly horizontal overhead covering using solid panels or open framing for full shade and clean modern lines. Provides strong weather protection and easy integration of lights or plants. Framing resists sagging and warping, ensuring long-term stability in low-wind outdoor spaces.
Gable Roof
Two sloping sides meeting at a central ridge, with triangular gable ends. Classic design that ensures good ventilation, ample headroom, and efficient water/snow shedding. Creates clean lines and timeless appeal in traditional outdoor setups.
Hipped Roof (Hip Roof)
A four-sided sloping roof with no vertical gable ends. Offers even weight distribution, strong wind resistance, and all-around water shedding. Provides an elegant, balanced look for long-lasting freestanding pavilions or large shade structures.
Louvered Roof (Adjustable Slat Roof)
Rotatable or fixed slats that adjust for sun, shade, or rain control. Offers versatile all-weather comfort and customizable coverage. Great for variable climates where flexibility matters.
Open Slat Roof (Traditional Pergola Roof)
Spaced parallel or crossed beams/rafters for dappled light, airflow, and vine support. Balances shade and openness with excellent ventilation. Perfect for classic pergolas with an airy, natural feel.
Polycarbonate Panel Roof (Solid Panel Roof)
Translucent or opaque panels for full UV/rain protection with diffused natural light. Creates bright, sheltered areas. Suited for attached shade structures or patios needing reliable, low-maintenance coverage.
Retractable Canopy Roof (Motorized or Manual Shade Roof)
Slide-open fabric or panel sections for on-demand shade that stacks away when unused. Preserves views and airflow. Ideal for seasonal outdoor spaces requiring flexibility between sun and shade.
Skillion Roof (Shed Roof / Mono-Pitch / Lean-To)
A single-sloped roof attached high on one side. Ideal for simple, directional water runoff in attached pergolas, lean-tos, or extensions. Delivers reliable drainage and a clean, modern appearance with low-maintenance performance in variable weather.
Stepped Roof
A roof configuration featuring two or more distinct horizontal levels, each offset vertically to create a staggered, tiered silhouette. The step between levels introduces architectural height and visual interest while also serving a functional purpose — the gap between tiers allows light, air, and rain drainage to pass through. Common in both covered and open-roof structures, and particularly effective on larger footprints where a single roof plane would feel flat or heavy. The stepped profile pairs well with modern, craftsman, and contemporary design style
Cupola
A small, decorative timber structure mounted at the peak of a roof — typically on a pavilion, gazebo, or cabana — that adds architectural height, visual interest, and a finished roofline focal point. Cupolas can be open-sided for ventilation or enclosed with louvered panels, and are available in square, hexagonal, or octagonal footprints to match the roof geometry below. A purely decorative upgrade that significantly elevates the perceived craftsmanship and presence of the structure.
Tiered Roof
A roof design featuring two or more distinct levels, each stepping up from the one below to create a layered, dimensional appearance. The gap between tiers often serves a functional purpose — allowing hot air to escape, improving ventilation, and letting light filter into the structure below. Tiered roofs are commonly seen on pergolas, pavilions, and gazebos where both aesthetics and airflow are priorities. The additional height and visual complexity of a tiered roof gives a structure a more custom, architectural look compared to a single-level roof. Also referred to as a double-tier roof or multi-tier roof when more than two levels are present.
Two-Story Pergola
A multi-level outdoor structure that combines a lower shaded living space with an upper open-air deck, connected by a staircase — often a spiral stair. The lower level typically features lattice privacy screens on the sides and a solid or slatted ceiling formed by the upper deck above, creating a sheltered patio space. The upper level is topped with a traditional pergola roof of spaced rafters and purlins for partial shade. Two-story pergolas are ideal for sloped lots, elevated decks, or homeowners who want to maximize their outdoor living on multiple levels. Also referred to as a double-decker pergola or elevated pergola.
Architectural & Interior Timber Work
Western Timber Frame’s architectural timber work spans residential and commercial applications at any scale — from interior ceiling systems in private homes to large-scale facade installations on hotels, hospitals, colleges, churches, restaurants, parks, and public infrastructure. WTF delivers either a complete fabricated timber package for contractor installation or handles the full project turnkey depending on the client’s needs.
Architectural Timber Awnings
Small skillion-style overhead structures mounted above windows, doors, or entry points on a building facade, supported by timber brackets and finished to match the surrounding architectural timber work. Primarily decorative, providing a minor weather break, shade, and strong visual definition to the building’s exterior. Common on hotels, commercial buildings, and high-end residential facades where the timber detailing extends across the full face of the structure rather than being limited to a single entry or covered porch. WTF provides the complete timber frame package — posts, brackets, and roof framing — finished and ready for installation by the general contractor.
Architectural Timber Accents
Decorative and structural timber elements — posts, beams, brackets, knee braces, and gable detailing — integrated into the exterior or interior facade of a building. Contribute to both appearance and structural performance. Common in mountain, craftsman, rustic, and contemporary architectural styles.
Coffered Ceiling
A ceiling system featuring a grid of intersecting beams with T&G or other finish materials filling the recessed panels between them. Produces a rich, layered overhead plane with significant visual depth — equally at home in a private residence or large commercial space.
Corbel (Architectural)
A shorter projecting timber extending from a wall, post, or beam to support an element above. Adds visual depth and handcrafted detail at transition points between vertical and horizontal surfaces. Distinguished from a timber bracket by scale — corbels are smaller and sit closer to the wall face.
Exposed Timber Ceiling
Interior beams and framing left intentionally visible rather than concealed behind drywall or finish ceiling materials. Adds warmth, architectural character, and craftsmanship to any space — from private great rooms to hotels and public buildings. Beams can be structural or decorative and are finished to match the design aesthetic of the space.
Exterior Timber Porches
Covered porch structures integrated into a building’s exterior, framed with heavy timber posts, beams, and roof framing. Extends the architectural language of the building’s timber work to the outdoor living space, engineered to the same standards as WTF’s standalone outdoor structures.
Gable Timber Detailing
Exposed timber framing installed within or around the triangular gable end of a building, typically including beams, knee braces, and corbels that define the roofline and add architectural identity to the facade.
Timber Ceiling System
The complete overhead assembly of beams, purlins, and infill panels working together as an integrated ceiling. Balances structure, aesthetics, and lighting integration. WTF engineers and fabricates complete ceiling systems for both interior and exterior covered spaces.
Rafter Hub (Crown)
The central structural and decorative element where all rafters converge at the peak of a gazebo or pavilion roof. In timber frame construction, the rafter hub is often one of the most visually striking components of the structure — rafters fan outward from a single carved or faceted wooden centerpiece, creating a sunburst or starburst effect when viewed from below. The hub must be precisely engineered to distribute roof loads evenly across all rafters while also serving as a signature design feature. Sometimes referred to as a crown, pendant, or king post hub.
Timber Knee Braces (Architectural)
Diagonal timber members connecting a vertical post to a horizontal beam on the exterior or interior of a building. Provide lateral stability and visual craftsmanship as part of the building’s framing — frequently seen on covered porches, entryways, and commercial facades.
Timber Brackets
Large projecting timber supports — angled or profiled — installed where a vertical surface meets a horizontal one. Typically larger and more prominent than corbels, often serving as a defining architectural feature on building exteriors, covered entries, and large overhangs. Can be decorative or fully structural.
Stair Railings & Timber Staircases
Custom timber stair systems — treads, stringers, newel posts, handrails, and balusters — designed to match the surrounding timber work. Fabricated for interior and exterior applications from private residences to commercial and hospitality settings. Engineered to meet applicable building codes for load, rise, run, and guardrail requirements.
Timber Trusses
Engineered triangulated timber frameworks spanning large distances to support roof or floor loads — left exposed as a primary architectural feature rather than concealed above a finish ceiling. Common in great rooms, churches, event venues, and commercial spaces requiring both long clear spans and dramatic overhead character.
Timber Columns
Large exposed vertical timber members inside a building supporting beams, roof loads, or upper floor framing while defining the character of the space. Common in great rooms, entryways, lobbies, and restaurants. Can be square, round, or custom-profiled.
Timber Entryway / Entry Portal
A freestanding or building-integrated timber frame that defines and announces an entrance — to a home, property, garden, or commercial space. Timber entryways combine structural presence with architectural character, creating a distinctive first impression. Can range from a simple post-and-beam portal to an elaborate gabled or arched entry structure.
Timber Fence
A timber-framed fence system built from heavy posts and horizontal rails, with infill of solid boards, lattice panels, or open spacing depending on the desired privacy, airflow, and aesthetic. Timber fences are engineered for long-term exterior durability and designed to complement the architectural character of the surrounding structures.
Timber Gate
A timber-framed gate designed for vehicular or pedestrian entry points, built to match the scale, species, and style of the surrounding fence or structure. Timber gates are engineered for the load and movement requirements of a swinging or sliding panel and hardware-matched for long-term exterior performance.
Curious how this applies to your project? We’re happy to help.
Structural Components
Beam
A primary horizontal timber that spans between posts and supports the rafters above. Beams run parallel to the house wall on an attached pergola, or parallel to each other on a freestanding structure. Beam size directly determines how far the structure can span between posts without deflecting (sagging) under load.
Header
A horizontal structural member that spans an opening — such as between two posts — and transfers the load above it to the posts on either side. In pergola construction, decorative headers between posts can add visual weight and frame the view from underneath the structure.
Ledger Board
A horizontal timber or engineered member bolted directly to the house wall on an attached pergola. The ledger serves as one of the two primary support lines — the equivalent of a beam, but mounted to the home’s structure rather than supported by posts. Proper ledger attachment is critical: an improperly installed ledger is one of the most common structural failure points in attached outdoor structures.
Post
A vertical timber that transfers the weight of the overhead structure down to the foundation. Posts are the primary load-bearing vertical members in any pergola or pavilion. Common sizes range from 4×4 (light residential) through 6×6, 8×8, and even larger for heavy timber construction. The size of the post determines the structure’s visual presence, structural capacity, and cost.
Purlin
Secondary horizontal members that run perpendicular to the rafters, adding shade density and visual layering. Purlins sit on top of the rafters and create the cross-hatched pattern characteristic of many pergola designs. In pavilions and roofed structures, purlins serve a structural role by supporting the roof decking.
Rafter
Horizontal members that form the “roof” of a pergola. On an attached pergola, rafters extend from the ledger board at the house wall outward to the beam. On a freestanding structure, rafters span from beam to beam. Rafters are typically spaced 12 to 24 inches apart and are the primary visual element when you look up at a pergola from underneath.
Raised Panel Posts
A structural timber post featuring recessed rectangular panels routed into or applied onto the face of the post. The raised panel detail is borrowed from traditional millwork and architectural column design, and is commonly associated with craftsman, colonial, and formal estate styles. It adds visual depth and dimension to the post face without altering the structural profile of the timber beneath.
Shade Plank
A flat, typically thinner board placed across the top of the rafters to increase shade coverage. Shade planks can be spaced closely for maximum shade or more widely for a lighter, airier feel. Common sizes include 2×4 and 2×6. The wider the shade plank, the higher the ShadePrint™ — WTF’s 8,000 Series uses 2×6 shade planks, producing 80%+ ShadePrint™ versus the 40–50% typical of competitors using narrower planks.
⚡ Why This Matters: Ask any pergola company what size shade planks ship with their standard kit and how they calculate shade coverage. ShadePrint™ is WTF’s proprietary metric for this — standard WTF kits average 80%+. Most conventional option kits, especially aluminum and light-frame wood, produce 40–50% — enough to hang string lights, not enough to keep guests comfortable at noon in July.
Knee Brace
A diagonal timber that connects a post to a beam at roughly a 45-degree angle, providing lateral stability and preventing racking (sideways movement). Knee braces are both structural and decorative — they add rigidity to the frame while creating the distinctive triangular detail seen in traditional timber construction.
Corbel
A short, projecting timber or bracket that extends from a post or wall to support a beam or rafter above. Corbels are primarily decorative in pergola construction, adding visual depth and a sense of craftsmanship at the post-to-beam connection.
T&G (Tongue and Groove)
Interlocking solid wood boards — each board has a protruding tongue on one edge and a matching groove on the other — that fit together to create a seamless, gap-free surface. T&G is one of the most versatile panel materials in timber construction. Used as ceiling decking in pavilions, gazebos, and cabanas for an elegant exposed-ceiling look; as interior ceiling infill between exposed beams in coffered and timber ceiling systems; as solid wall panels for full enclosure; and as overhead or vertical privacy and shade panels when full coverage is required. Blocks rain and sun completely outdoors while adding warmth and a finished timber aesthetic to interior spaces.
Gable End
The triangular section formed by the slope of a roof at the end of a structure. In pavilions and roofe pergolas, the gable end is a prominent design feature that can be left open, enclosed, or detailed with decorative accents.
Ridge Beam
The horizontal timber at the highest point of a gable or pitched roof, running the full length of the structure. Rafters connect to the ridge beam at the peak. Not all pergola designs require a ridge beam — it depends on whether the roof is flat, pitched, or gabled.
Fascia
A board or timber that runs along the outer edge of the rafter tails, creating a finished, vertical face along the perimeter of the structure. Fascia gives the structure a clean, defined edge and can be shaped or profiled for decorative effect.
Rafter Tail
The portion of a rafter that extends beyond the beam, creating an overhang. Rafter tails are often cut into decorative profiles — curves, angles, or stepped designs — that become one of the most visible architectural details of the structure.
Joist
A horizontal structural member that supports floor or deck loads, spanning between beams or walls. In outdoor timber structures, joists support decking material and transfer live and dead loads to the primary beams below. Joist sizing depends on span, spacing, species, and the loads the deck or floor must carry.
Decking
The surface material laid over joists to create a walkable floor or deck plane. In timber structures, decking is typically solid wood boards — 2×4, 2×6, or wider — installed with spacing for drainage and expansion. Species selection for decking prioritizes durability, slip resistance, and dimensional stability under foot traffic and weather exposure.
Brace Frame
The overall system of diagonal members — knee braces, cross braces, or engineered panels — within a timber structure that resists lateral loads from wind and seismic forces. A well-designed brace frame keeps the structure square and stable under horizontal loading without relying solely on connection hardware. Critical in tall structures, long spans, and high-wind or seismic zones.
Deck Railing
The system of vertical posts, top and bottom rails, and infill — balusters, lattice panels, or metal — that encloses the perimeter of a deck for safety and visual definition. Engineered to meet code requirements for height and load resistance.
Deck Ledger
A horizontal timber bolted directly to a building’s wall framing that serves as one of the primary support members for an attached deck. The deck ledger transfers the deck’s load to the home’s structure and must be properly flashed and waterproofed to prevent moisture infiltration at the wall connection — one of the most common failure points in attached deck construction.
Collar Tie
A horizontal timber connecting two opposing rafters at a point above the wall plate, preventing the rafters from spreading outward under load. Collar ties are a critical component in gabled roof systems — they resist the lateral thrust that a pitched roof exerts on the walls below. Often left visible as an architectural feature in exposed timber roof systems.
King Post
The central vertical timber in a triangular roof truss, running from the apex down to the center of the bottom chord. The king post resists the downward pull of the bottom chord and is one of the simplest and most recognizable truss configurations in timber construction. Common in gabled pavilions, covered bridges, and exposed timber roof systems.
Queen Post
A truss configuration using two vertical posts set symmetrically on either side of the center rather than a single central king post. Queen post trusses span wider openings than king post trusses and create an open center panel that can be left clear or filled with decorative timber work. Common in larger pavilions, great rooms, and commercial timber structures.
Cantilever
A structural member — beam, rafter, or deck section — that projects beyond its last point of support without any support at the free end. Cantilevered elements must be carefully engineered to resist the upward bending forces at the support point and downward deflection at the tip. Common in deck overhangs, extended roof eaves, and dramatic architectural projections.
Stepped Deck
A deck configuration featuring two or more distinct platform levels connected by steps, each offset vertically to follow a grade change, define separate use zones, or add architectural interest. Stepped decks are common on sloped lots where a single flat platform would require excessive framing height, and on larger properties where distinct areas — dining, lounging, poolside — benefit from visual and physical separation. Each level is independently engineered for its own load requirements and footing conditions.
Panels, Enclosures & Screens
Shade Panels
Any panel — lattice, T&G;, polycarbonate, or louvered — installed in the overhead plane of a structure or targeted area to reduce direct sunlight and heat beneath. Shade panels differ from open slat roofs in that they provide a more continuous surface with less gap, increasing coverage and thermal comfort. The material chosen determines the degree of shade, light quality, and aesthetic. Lattice shade panels allow dappled light and airflow; T&G; shade panels provide full blockage; polycarbonate panels diffuse light while blocking UV.
Lattice Panels
Crisscrossed strips forming an open, decorative framework for partial shade, airflow, and vine support. Delivers dappled light without full enclosure. Adds timeless elegance and an airy feel to pergolas and outdoor structures.
Solid T&G Panels (Solid Tongue-and-Groove Panels)
Interlocking solid wood boards creating a seamless, watertight overhead surface for full shade and weather protection. Blocks rain and sun completely with a smooth, finished look. Provides elegant exposed-ceiling appeal and reliable coverage in covered patios or pavilions.
Privacy Panels
Vertical or overhead panels (latticed or solid) designed to block views, wind, or sun while maintaining an open or enclosed feel. Latticed versions allow partial airflow and light; solid versions provide full seclusion and weather protection. Creates defined, comfortable outdoor rooms in pergolas, patios, or shade structures.
Solid Wood Blinds (Heavy-Duty Blinds)
Thick, durable solid wood slats mounted horizontally or vertically, adjustable to control light, privacy, and airflow. Built for strength and longevity in outdoor exposure. Offers robust screening and a premium, natural appearance for pergola sides, pavilions, or covered seating areas needing heavy-duty performance.
Shutters (Heavy-Duty Wood Blinds)
Shutters are adjustable or fixed slatted panels integrated into a timber structure to provide privacy, shade, and light control. Shutters are often installed along the sides of pergolas, pavilions, or cabanas to create a more enclosed and comfortable space. Depending on their design, they can filter sunlight, reduce glare, and allow airflow while maintaining a sense of openness.
Joinery & Connections
Mortise and Tenon
The foundational joint of timber frame construction. A mortise is a cavity cut into one timber; a tenon is the shaped projection on the end of the joining timber that fits into the mortise. When properly cut and pegged, this joint resists both gravity loads and lateral forces. It has been used in timber construction for thousands of years — and it’s still the gold standard.
Dovetail
A joint shaped like a dove’s spread tail, designed to interlock two timbers so they resist pulling apart. Dovetails are exceptionally strong joints used in gravity-load conditions — where one timber sits on or into another. The interlocking geometry means the joint gets tighter under load rather than loosening. Our Dovetail Difference™ joinery system is based on this principle.
Dovetail Difference™ (See The Dovetail Difference®)
Termed by Western Timber Frame for their award winning Post-to-Beam Dovetail Connection System combining heritage
architectural principles with state of the art technology in all of their timber frame DIY pergolas, pavilions, gazebos, arbors and outdoor structures.
Compound Angle Joint
A connection where timbers meet at non-standard angles — not 90 degrees — requiring cuts on multiple axes simultaneously. Compound angle joinery is necessary when a pergola interfaces with a hip roof, wraps around an architectural feature, or follows the slope of a hillside lot. This is among the most technically demanding joinery in the industry and requires CNC equipment capable of multi-axis cutting.
Butt Joint
The simplest connection: two square-cut timber ends placed against each other. Butt joints have minimal inherent strength and rely on fasteners, hardware, or gravity to stay connected. Common in kit pergolas and light-frame construction. Not used in precision timber framing.
Trunnel (Treenail)
A large wooden dowel or peg used to lock a mortise-and-tenon joint. The word derives from “tree nail.” In traditional timber framing, the trunnel holes in the mortise and tenon are deliberately offset slightly (a technique called draw boring) so that driving in the peg pulls the joint tight.
Draw Boring
A technique where the peg holes in the mortise and tenon are intentionally offset. When the trunnel is driven through both holes, it draws the tenon deeper into the mortise, pulling the joint extremely tight. Draw boring creates a mechanical lock that holds without any metal fasteners.
Housing
A shallow mortise or recess cut into one timber to receive the full end of another, providing a seat that resists rotation and distributes load across a wider surface. Housing is often combined with a deeper mortise-and-tenon within the same joint for maximum strength.
CNC (Computer Numerical Control)
Automated cutting technology that uses computer-programmed instructions to control cutting tools with extreme precision. In timber fabrication, CNC machines can execute complex compound angle cuts, mortise pockets, and dovetail profiles that would be extraordinarily difficult (or impossible) to achieve consistently by hand. CNC precision is what allows custom timber companies to produce joints that fit perfectly on the first assembly.
Post-to-Beam Connection
The critical joint where the top of a vertical post meets the horizontal beam it supports. This connection must transfer both downward (gravity) loads and lateral (wind and seismic) forces. The method used — mortise-and-tenon, steel bracket, concealed hardware, or bolted plate — fundamentally determines the structural integrity, aesthetics, and longevity of the structure.
Rafter Guide Slots
Pre-cut notches or slots milled into a beam or purlin that indicate exactly where each rafter should be positioned during installation. Guide slots eliminate the need for measuring and marking rafter spacing on site, ensuring consistent, precise spacing across the entire structure every time. They also serve a structural purpose — by cradling the base of each rafter, guide slots help lock the members in place and resist the natural tendency of wood to warp, twist, or shift over time. A feature of precision-milled timber frame kits that significantly simplifies installation and improves the finished appearance of the roof line.
Housed Dovetail
A dovetail joint where the tenon fits into a mortise that also includes a shallow housing — a wider, flat-bottomed recess — around the joint. The housing provides a larger bearing surface, distributes load more evenly, and resists rotation at the connection point. Stronger and more stable than a basic dovetail mortise alone.
Blind Dovetail (Secret Dovetail)
A dovetail joint that is fully concealed — no part of the joint is visible from the exterior once assembled. Requires extremely precise cutting and fitting but produces a seamless, all-wood appearance with no visible joinery. Used where aesthetics demand a completely clean timber face without sacrificing structural integrity.
Half-Lap Dovetail
A joint that combines half-lap and dovetail geometry — half the thickness of each timber is removed at the connection point, and the mating surfaces are cut with dovetail angles to resist separation under load. Provides a flush, low-profile connection with the mechanical locking strength of dovetail geometry.
The Dovetail Difference® / Dovetail Difference™
The Dovetail Difference® is Western Timber Frame’s patented precision joinery system — the most significant structural and aesthetic innovation in the timber frame pergola industry. Invented and designed by Hyrum Thompson, founder and CEO of Western Timber Frame, Inc., the system is protected by United States Patent No. 9,797,149 B2 (issued October 24, 2017) and federally registered under Trademark Registration No. 5,174,850 (registered April 4, 2017, Class 019 — Timber frame structures with dovetail joints). The Dovetail Difference® is owned exclusively by Western Timber Frame, Inc.
The Dovetail Difference® is the patented improved joint assembly that connects timber support beams to timber support posts using a precision-engineered tail-and-socket system. Each beam end is CNC-cut into a wedge-shaped tail with a specific geometry — an outer face angled at approximately 8 degrees — that slides vertically down into a complementary socket formed in the post. The socket is precisely dimensioned to receive the tail through a drop-in-place procedure requiring no bolts, no lag hardware, and no surface-mounted connectors at the post-to-beam connection point. The result is a completely clean, all-wood connection visible from every angle — with no metal hardware showing anywhere in the finished structure.
What makes the Dovetail Difference™ structurally superior to conventional joinery is the geometry itself. The wedge-shaped tail fits into a socket whose tapered sidewall undercuts the outer face of the tail. As load is applied — the weight of the structure, wind forces, seasonal movement — the joint geometry causes the connection to tighten rather than loosen. Conventional bolted connections loosen over time as wood expands and contracts and fasteners work against the timber. The Dovetail Difference® joint does the opposite: it locks itself tighter with every load cycle, every season, every year. The patent covers timber frame structures including pergolas, patio covers, pavilions, trellises, arbors, gazebos, and decks.
⚠ NOTICE TO BUYERS — IMPOSTORS EXIST
The Dovetail Difference® is a patented, federally trademarked system owned exclusively by Western Timber Frame™, Inc. Other companies have attempted to claim, copy, or imply ownership of this joinery system online. They cannot. If a competitor uses the name The Dovetail Difference® or Dovetail Difference™, claims dovetail joinery identical to WTF, or implies patent ownership of this system, they are misrepresenting their product. The patent is public record: US 9,797,149 B2. The trademark is registered: Reg. No. 5,174,850. Both are owned by Western Timber Frame, Inc. exclusively.
What to look for: Ask any pergola company claiming dovetail joinery for their patent number. If they cannot provide one, they do not have one. There is only one patented dovetail joinery system in the timber frame pergola industry. You are reading about it now.
Wood Science & Materials
Species
The biological type of tree from which lumber is milled. Different species have different structural properties (strength, stiffness, weight), durability ratings (resistance to rot, decay, and insects), visual characteristics (grain pattern, color, texture), and cost. The three most common species in custom timber pergola construction are Douglas Fir, Coast Redwood, and Western Red Cedar.
Douglas Fir
One of the strongest commercially available softwoods, widely used in heavy timber construction. The Western Wood Products Association rates Douglas Fir-Larch with a Modulus of Elasticity (stiffness) of 1,900,000 psi — among the highest of any softwood species. Excellent for structural applications where beam spans and load-bearing capacity are critical. The USDA Forest Products Laboratory classifies Douglas Fir as “Moderately Durable” (Class 3) against decay, meaning it requires protective finish or treatment for long-term exterior performance.
Coast Redwood (Sequoia sempervirens)
A premium softwood species prized for its natural decay resistance, dimensional stability, and distinctive reddish color. The USDA Forest Products Laboratory classifies Coast Redwood as “Durable” (Class 2), meaning the wood’s own natural chemistry resists rot and insect damage without chemical treatment. Coast Redwood in the large structural dimensions required for heavy timber construction (8×8 posts, 4″x14″ beams) is extremely difficult to source — very few manufacturers have the mill relationships to deliver it.
Western Red Cedar (Thuja plicata)
A naturally durable softwood valued for its resistance to moisture, decay, and insect damage. The USDA Forest Service attributes Cedar’s durability to specific fungicidal compounds called thujaplicins — natural extractives in the heartwood that actively resist biological degradation. Cedar is lighter and less structurally strong than Douglas Fir, but its natural rot resistance makes it an excellent choice for high-moisture environments.
Incense Cedar (Calocedrus decurrens)
A naturally durable softwood prized for its resistance to moisture, decay, and insect damage. Like Western Red Cedar, its durability stems from thujaplicin compounds concentrated in the heartwood that actively resist biological degradation. Incense Cedar offers outstanding dimensional stability — resisting warping and checking in variable weather — and a fine, even grain that machines cleanly and absorbs stains consistently. Lighter than Douglas Fir but with superior natural rot resistance, it’s an excellent choice for pergolas and outdoor timber structures where performance, longevity, and a polished finish all matter
Equilibrium Moisture Content (EMC)
The moisture level at which wood stops gaining or losing moisture relative to its surrounding environment. EMC is determined by ambient temperature and relative humidity — not by how the wood was originally dried. Outdoor EMC across the United States ranges from approximately 4–8% in arid desert climates to 12–16% in humid coastal regions. No matter what moisture content timber starts at, it will always drift toward the EMC of its environment over time. This is why matching timber to its installation environment matters more than hitting a specific kiln target. Learn more →
Lumber Grade
A classification system that rates lumber based on structural properties, visual appearance, and allowable defects (knots, wane, splits). Higher grades have fewer defects, straighter grain, and more consistent structural performance. Grade A (or Select Structural) is the highest standard. Lower grades may be structurally adequate but will have more visual imperfections and less predictable performance over time.
Green Wood
Freshly milled wood that has not been artificially dried, typically carrying a moisture content of 80–120% or higher. Green timber is the standard specification for heavy timber framing and large outdoor structures — not a budget alternative to kiln dried wood. Large-dimension timbers cannot be kiln dried without significant risk of internal cracking and stress damage, so green timber is used intentionally. As it dries in place, well-engineered joints tighten rather than loosen, and surface checks that develop are cosmetic, not structural.
Air Dried (AD)
Lumber dried naturally by stacking with spacers between layers to allow airflow, rather than in a heated kiln. Air drying brings timber to a moisture content of approximately 12–19% — close to the equilibrium moisture content wood naturally reaches in most outdoor environments. For heavy structural timber, air drying is the industry standard. Timber installed near its in-service moisture level moves less, stresses connections less, and in traditional timber frame joinery, actually tightens as it finishes drying in place. Surface checks that develop during this process are cosmetic, not structural. Learn more about air dried vs. kiln dried timber →
Kiln Dried (KD)
Lumber dried in a controlled heated chamber, typically to 6–9% moisture content. Kiln drying is the right choice for furniture, flooring, and interior millwork in climate-controlled environments. For heavy structural timber outdoors, it is generally the wrong specification — outdoor timber will reabsorb moisture until it reaches equilibrium with its surrounding environment regardless of how it was dried. Air dried timber, installed closer to its in-service moisture content, is the industry standard for timber frame outdoor structures. See our blog post on kiln dried lumber →
Checking
Small surface cracks that run parallel to the grain as the outer layers of timber dry and shrink faster than the interior. Checking is a normal and expected part of solid heavy timber — every piece of large-dimension wood will check to some degree regardless of species or how it was dried. It is cosmetic only and does not affect structural performance. Checking is different from splitting (a crack through the full thickness) and shaking (separation along the growth rings), both of which can indicate a material defect. A checked timber is simply a timber that is seasoning. Learn more →
Shake
A separation that occurs along the growth rings of a timber, as opposed to checking which occurs across the grain. Shakes can be structural concerns depending on their severity and location. Not to be confused with “shake” as a roofing material (split wood shingles).
Heartwood
The older, non-living wood at the center of a tree trunk, typically darker in color than sapwood. Heartwood containing the pith — the very center of the tree — is prone to checking, cracking, and dimensional instability in large-dimension timber applications. For this reason WTF specifies Free of Heart Center timber for structural and finish work.
Honeycombing
Internal cracks that form inside a timber when it is kiln dried too aggressively. When the outer shell dries and shrinks faster than the wet interior can keep up with, internal fractures develop that are invisible from the outside — the timber can look perfectly sound on the surface while being compromised within. Honeycombing is one of the primary risks of kiln drying large-dimension timbers, and one of the reasons Western Timber Frame uses air dried timber for structural work rather than forcing large-section wood through a kiln. Learn more about timber drying →
FOH (Free of Heart Center)
A lumber specification requiring that the pith — the unstable central core of the tree — be excluded from the timber. Free of Heart Center timber is more dimensionally stable, less prone to checking and cracking, and performs more consistently in heavy timber construction. A standard WTF specification for structural and finish applications.
Sapwood
The younger, lighter-colored wood between the heartwood and the bark. Sapwood is actively transporting water and nutrients in a living tree. It is less dense, less decay-resistant, and more prone to insect attack than heartwood. In exterior applications, sapwood is the first area to deteriorate if not properly protected.
Modulus of Elasticity (MOE)
An engineering measurement of a wood species’ stiffness — its resistance to bending under load. Higher MOE means the beam will deflect less under the same load. MOE is one of the most important values in beam sizing calculations because it determines how much a beam will sag over a given span. Published in the NDS Supplement by the American Forest & Paper Association.
Moisture Content (MC)
The percentage of water weight in a timber relative to its dry weight. Moisture content directly affects a timber’s weight, dimensional stability, and behavior in joinery. Green wood typically has MC above 19%; kiln dried lumber is brought to 19% or below. MC is one of the most important variables in predicting how a timber will perform after installation.
Fiber Bending Strength (Fb)
The maximum bending stress a wood species can resist before failure. While MOE tells you how much a beam will bend, Fb tells you how much it can bend before it breaks. Both values are essential for proper structural engineering. Published in the NDS Supplement by the American Wood Council
Specific Gravity
The density of a wood species relative to water. Higher specific gravity means heavier, denser, generally stronger wood. Douglas Fir has a higher specific gravity than Cedar, which is why it’s heavier per board foot but structurally stronger.
Dimensional Stability
A wood species’ resistance to expanding, contracting, warping, and twisting as moisture content changes. Coast Redwood is exceptionally dimensionally stable, which is one reason it performs well in exterior applications where temperature and humidity fluctuate constantly.
Extractives
Natural chemical compounds in certain wood species that provide resistance to decay, insects, and fungi. Cedar’s thujaplicins and Redwood’s tannins are extractives. Species with high extractive content are considered naturally durable and require less chemical treatment for exterior use.
Board Foot
The standard unit of lumber measurement, equal to a piece of wood 12″ × 12″ × 1″ thick. Used to calculate material volume and cost across any timber dimension. A single 8×8 post 10 feet long contains 53.3 board feet. Understanding board footage helps homeowners compare material estimates across different species, grades, and suppliers.
Reclaimed Timber
Lumber salvaged from existing structures — old barns, warehouses, industrial buildings, bridges, and mills — and repurposed for new construction. Reclaimed timber is prized for its aged character, tight grain, rich patina, and the story it carries. Often old growth material that is no longer available from new-harvest sources. WTF has sourced and incorporated reclaimed timber on specialty projects where the aesthetic or historical character of the material is central to the design intent.
Rough-Sawn
Lumber that has been cut at the sawmill but not surfaced or planed smooth. Rough-sawn timber retains the saw marks and slight irregularities from milling, giving it a raw, textured appearance with slightly larger actual dimensions than surfaced lumber. Preferred for rustic, naturalistic, and traditional timber aesthetics where a handcrafted look is desired.
Smooth-Sawn (Surfaced / Dressed)
Lumber that has been planed on one or more faces after sawmill cutting, producing a clean, consistent surface. Smooth-sawn timber has more precise dimensions, absorbs stain more evenly, and presents a refined, finished appearance. Standard for most WTF structures where a polished, architectural look is required.
Flat Grain (Flat-Sawn)
Lumber cut so that the growth rings run roughly parallel to the face of the board. Flat grain timber shows a broad, cathedral-like grain pattern and is the most common cutting method because it yields the most usable lumber from a log. More prone to cupping and surface checking than vertical grain lumber.
Vertical Grain (Edge-Grain / Quarter-Sawn)
Lumber cut so that the growth rings run perpendicular to the face of the board. Vertical grain timber is more dimensionally stable, more resistant to cupping and warping, and wears more evenly than flat grain lumber. Typically more expensive due to the lower yield per log. Preferred for high-performance exterior applications and fine finish work.
Knot
A circular or oval grain irregularity in lumber caused by a branch that was enclosed within the growing tree. Knots affect both appearance and structural properties — tight knots are firmly embedded and generally acceptable; loose or dead knots can fall out over time. Lumber grading systems evaluate knot size, frequency, and location as primary factors in determining structural and visual grade.
Glulam (Glue-Laminated Beam)
An engineered wood product made by bonding multiple layers of dimensioned lumber together with structural adhesive, with the grain of all layers running parallel. Glulam beams can achieve longer spans and carry greater loads than comparably sized solid timber, and are available in dimensions that exceed what can be milled from a single log. Used in heavy timber construction where span, load, or availability makes solid timber impractical.
Curved Glulam (Arched Glulam)
A glue-laminated beam manufactured with a deliberate curve or arch by laminating thin layers of lumber under pressure before the adhesive sets. Curved glulam enables dramatic arched spans, vaulted ceilings, and flowing rooflines that would be impossible to achieve with solid timber. Commonly used in pavilions, event structures, churches, and large-scale architectural timber applications where both structural performance and visual impact are required.
Tangential and Radial Shrinkage
The two primary directions wood shrinks as it loses moisture, and the reason wood doesn’t move evenly as it dries. Radial shrinkage occurs across the growth rings (toward the center of the tree) while tangential shrinkage occurs along the growth rings. The key distinction: tangential shrinkage is roughly twice as great as radial shrinkage — meaning a piece of wood shrinks significantly more around the rings than it does toward the center. This difference in shrinkage rates is what causes checking, warping, cupping, and twisting as timber dries. It also explains why the way a board is cut from the log — plain sawn, quarter sawn, or rift sawn — affects how stable it will be over time.
Plain Sawn
The most common and most affordable cutting method, where the log is cut straight through in parallel slices. Plain sawn boards show the characteristic arching or cathedral grain pattern on the face. Because the growth rings run at a low angle to the face, plain sawn timber is more prone to cupping and warping as it dries but yields the widest boards with the least waste.
Quarter Sawn
A cutting method where the log is first quartered and then each quarter is cut so the growth rings run closer to perpendicular to the face. Quarter sawn timber is significantly more dimensionally stable than plain sawn, less prone to cupping, and shows a tighter, more uniform grain pattern. More costly to produce due to greater waste in the milling process.
Rift Sawn
The most stable and most expensive cut, where each board is sawn at a consistent angle to the growth rings — typically around 45 degrees. Rift sawn timber shows a very straight, uniform grain with minimal ray fleck and is the least likely to cup, twist, or warp. Rarely used in structural timber framing due to cost and waste but prized for fine interior woodwork and flooring.
Engineering & Building Codes
Dead Load
The permanent, static weight of the structure itself — timbers, hardware, roofing material, and any permanently attached elements. Dead load doesn’t change over time. Engineers must account for dead load in every structural calculation.
Deflection
The amount a beam bends under load, measured as a fraction of the span (e.g., L/180 means the beam deflects 1 inch over a 180-inch span). Building codes set maximum allowable deflection ratios. However, code-minimum deflection and “the beam won’t visibly sag over 20 years” are two very different standards.
Dynamic Load
A live load that involves motion — such as a porch swing, a hammock, or wind gusts. Dynamic loads create stress patterns that static loads do not, including lateral forces and impact forces. A 200-pound person on a stationary chair is a static live load. That same person on a moving swing is a dynamic load that concentrates force at a single point while adding lateral momentum. Structures must be engineered differently for dynamic loads.
Lateral Load
Horizontal forces acting on a structure — primarily wind and seismic activity. Unlike gravity loads which act straight down, lateral loads push sideways and must be resisted through diagonal bracing, knee braces, engineered connections, or post embedment. Lateral load resistance is one of the primary engineering considerations in any outdoor timber structure, particularly in high-wind or seismic zones.
Live Load
Any temporary or variable load on the structure — people standing on it, furniture, snow accumulation, hanging plants, lighting fixtures, swings, and wind. Live loads change constantly and are the primary reason structures need to be engineered beyond minimum dead-load capacity. Standard residential patio covers are often rated for just 10 pounds per square foot (psf) of live load, which is a maintenance-access rating — not a “host a dinner party with a porch swing” rating.
⚡ Why This Matters: 10 psf live load is code minimum for basic patio covers — barely enough for someone walking across the roof for maintenance. If you plan to hang a swing, a ceiling fan, heaters, speakers, or have guests gathered underneath during a windstorm, ask for the specific live load rating your structure is engineered to handle.
Load Path
The route forces travel through a structure from the point of application down to the foundation. A complete, uninterrupted load path — from roof load through rafters, beams, posts, and footings into the ground — is the fundamental requirement of any engineered structure. Weak or missing connections anywhere in the load path compromise the entire system regardless of how well the rest is built.
Point Load
A concentrated force applied to a single location in a structure — as opposed to a distributed load spread evenly across a surface. Common examples include a post transferring beam loads to a footing, or a swing or hammock attachment concentrating dynamic force at one connection point. Structures must be specifically engineered at point load locations to prevent failure.
PSI (Pounds per Square Inch)
PSI stands for pounds per square inch, a unit of pressure used to measure how much force is applied to a specific area. In construction and timber framing, PSI is commonly used to describe material strength, load capacity, and resistance to stress. Understanding PSI ensures that a structure is engineered for durability, safety, and long-term performance—especially in environments with heavy snow loads, wind, or daily use.
PSF (Pounds per Square Foot)
PSF stands for pounds per square foot, a unit of measurement used to describe how much weight is distributed across a given area. In construction, PSF is most commonly used to define snow load on roofs.
⚡ Why This Matters: If you’re in a mountain market — PSF is critical for ensuring your structure is built for your specific environment. Snow loads vary by region, and properly engineering for PSF ensures long-term strength, safety, and performance—especially in areas with heavy snowfall.
Snow Load
The weight of accumulated snow on a structure, measured in pounds per square foot. Snow load requirements vary dramatically by region, elevation, and local building code. The latest national standard — ASCE 7-22 — introduced reliability-targeted ground snow loads that are 12% higher on average than previous editions. A pergola engineered to the 2016 code may not meet 2022 requirements in your jurisdiction.
⚡ Why This Matters: If you’re in a mountain market — Park City, Wasatch Front, Colorado, Vermont — ask your pergola company which edition of ASCE 7 their engineering references. Structures engineered to older editions may be undersized for current code requirements, creating permitting problems and liability exposure.
Wind Load
The force exerted on a structure by wind, including both positive pressure (wind pushing against a surface) and negative pressure (suction on the leeward side). Solid-roof structures like pavilions have significantly higher wind load requirements than open-rafter pergolas because a solid roof acts as a sail. Wind load engineering is especially critical in coastal, hurricane-prone, and high-altitude regions.
Span
The unsupported distance a beam covers between posts. The longer the span, the deeper and stiffer the beam must be to resist deflection. Span-to-depth ratio is one of the most important engineering calculations in pergola design — an undersized beam over a long span is the primary cause of structural sagging.
Frost Line (Frost Depth)
The maximum depth to which the ground freezes in a given region. Footings must extend below the frost line to prevent the structure from heaving (lifting and shifting) during freeze-thaw cycles. Frost depth ranges from 12 inches in the southern U.S. to over 48 inches in northern mountain climates. Local building codes (IRC R403.1.4.1) mandate minimum footing depths based on this measurement.
Stamped Structural Drawings (Engineered Plans)
Construction drawings that have been reviewed, sealed, and signed by a licensed Professional Engineer (P.E.), certifying that the structure meets applicable building codes. Required for permitting in most jurisdictions. “Stamped” refers to the engineer’s official seal on the documents. Structures built without stamped drawings may not be permitted, insured, or compliant — and may create problems at resale.
Pergola Bracing
Structural members added to a pergola frame to resist lateral forces — the sideways movement caused by wind, seismic activity, and racking. Without adequate bracing, a pergola frame can shift, lean, or collapse under load even if the individual posts and beams are strong. Common bracing types include knee braces (angled members connecting posts to beams), cross bracing (X-shaped members between posts), and let-in bracing (braces recessed into the face of a post or beam for a cleaner appearance). The type, size, and placement of bracing is determined by the structure’s size, local wind and snow loads, and engineering requirements. In regions with high wind or seismic activity, bracing specifications are typically reviewed and stamped by a licensed structural engineer.
ASCE 7
The national standard published by the American Society of Civil Engineers that defines minimum design loads for buildings and other structures — including wind, snow, rain, earthquake, and flood loads. The current edition is ASCE 7-22. This standard is referenced by virtually all U.S. building codes and determines the engineering requirements for any permitted outdoor structure.
IRC (International Residential Code)
The model building code adopted by most U.S. jurisdictions for residential construction. IRC Appendix AH specifically addresses patio covers and outdoor structures, governing structural requirements, setbacks, and permitting classifications. Whether your project is classified as a “pergola” or a “patio cover” under the IRC can affect what permits you need and where on your lot you can build.
NDS (National Design Specification for Wood Construction)
Published by the American Forest & Paper Association, this is the definitive reference for engineering calculations involving wood structures. The NDS Supplement contains the design values (MOE, Fb, specific gravity) for every commercial lumber species and grade. Any legitimate structural engineer designing a timber pergola is referencing NDS values.
Setback
The minimum distance a structure must be placed from a property line, easement, or other boundary, as defined by local zoning codes. Solid-roof structures (pavilions) often have different setback requirements than open-roof structures (pergolas). This is one reason the pergola-vs-pavilion terminology distinction matters legally, not just aesthetically.
Seismic Zone
A geographic classification indicating the level of earthquake risk in a given region, used to determine the seismic load requirements a structure must be engineered to resist. Higher seismic zones require more robust lateral bracing, stronger connections, and more conservative engineering. The current national standard — ASCE 7-22 — maps seismic design categories across the U.S. and is referenced by local building codes for all permitted structures.
Uplift Force
An upward force acting on a structure caused by wind passing over and under the roof surface, creating negative pressure that tries to lift the structure off its foundation. Uplift forces are especially significant in open-rafter pergolas and solid-roof pavilions and must be specifically engineered at the post base connections and footings. A primary reason post anchors and knife plates are engineered rather than decorative.
Zoning
Local government classification of land use determining what can be built, where, and how large. Residential, commercial, and agricultural zones each carry different rules for outdoor structures. Zoning classification should be confirmed before design begins — it determines setbacks, height limits, and permitted uses.
Variance
A formal request to a local zoning or building authority to deviate from a standard requirement — setback, height, or size — when strict compliance isn’t practical for the site. Requires application, review, and approval before construction can proceed. Not guaranteed.
Hardware & Protection Systems
Knife Plate (EarthAnchor™ Structural Knife Plate)
A structural metal plate installed between the base of a post and the footing to prevent direct wood-to-ground contact. Knife plates elevate the timber above the surface where moisture accumulates, dramatically reducing the risk of rot, decay, and insect damage at the structure’s most vulnerable point. Our EarthAnchor™ Structural Knife Plates are custom-engineered structural aluminum — they are not available at retail stores. They serve dual purpose: moisture barrier and structural anchor, and contribute to 120+ mph wind ratings. Once installed, the knife plate is completely concealed within the timber post — invisible from the exterior.
⚡ Why This Matters: Ask any pergola company: “What protects the base of the post from moisture?” If the answer is “the post sits in a bracket” or “the concrete is sloped away” — that’s not moisture protection. That’s hoping water cooperates. The post base is where rot always begins, because it’s where moisture accumulates and where you can’t see the damage until it’s structural.
Post Base (Post Anchor)
Any hardware that connects the base of a post to the footing or concrete slab. Post bases can be surface-mounted, embedded in concrete, or integrated with knife plates. The connection must resist both downward gravity loads and lateral forces from wind and seismic activity.
Cap System (Patent Pending)
A protective element that seals the top joint area of a post — where the post meets the beam — to prevent water from infiltrating the joint and accelerating wood decay. Top-joint moisture is one of the most overlooked deterioration points in outdoor timber structures because water pools in the horizontal surfaces of the connection.
Concealed Hardware
Structural connectors designed to be hidden within the joint so that no metal is visible from the exterior. Concealed hardware preserves the clean, all-wood aesthetic of traditional timber framing while providing the engineering-grade load transfer required by modern building codes.
Simpson Strong-Tie
The dominant manufacturer of structural connectors, post bases, joist hangers, and engineered hardware in the U.S. construction industry. Simpson products define the “load path” standards that most contractors and engineers reference. In custom timber framing, Simpson hardware is sometimes used for specific connections, but custom-engineered connectors are required for many heavy timber joints that standard catalog products can’t accommodate.
Galvanized Hardware
Steel hardware coated with a layer of zinc to resist corrosion. Standard for most inland installations. In coastal environments, galvanized hardware may corrode faster than expected due to salt air exposure, in which case stainless steel hardware is recommended.
Stainless Steel Hardware
Hardware manufactured from stainless steel alloys that resist corrosion far more effectively than galvanized steel. Required or strongly recommended for coastal installations and environments with high salt exposure. More expensive than galvanized but essential for the long term integrity of structures near the ocean.
Hardware Package
The complete set of engineered fasteners, connectors, and accessories that ships with every WTF/PergolaScape kit. Every hardware package is specced to the structural requirements of the individual project — not generic off-the-shelf components. A typical package includes: EarthAnchor™ Structural Knife Plates, engineer-grade timber lags in various lengths (5″ to 14″), high-strength structural screws, connector bits, additional lags, concrete bolts, bit adapters, touch-up stain, and the patent-pending cap system. The package is designed so the installer has every fastener and driver needed for assembly without sourcing anything separately.
Engineer-Grade Timber Lags
Heavy-duty lag bolts specced for standard-engineered timber connections. Included in every hardware package in various lengths from 5″ to 14″, sized to match the specific timber dimensions and load requirements of the kit. Unlike generic lag bolts, these are selected based on the structural engineering of each individual project.
TimberVolt™ Power Post System
A proprietary upgrade that integrates electrical wiring inside the pergola posts, eliminating the need for visible cords, surface-mounted conduit, or post-installation electrician work. Posts are drilled through to create internal wiring pathways, and electrical boxes are routed out within the timber to accept standard components. The system is pre-wired in the shop — posts arrive ready for connection. TimberVolt® enables lighting, fans, heaters, outlets for TVs and speakers, and any standard 120V application. It is the most popular upgrade across all PergolaScape™ kits. Structures with TimberVolt® cost more upfront but typically cost less than retrofitting power after construction — and the result is far cleaner because the wiring is invisible and protected inside the timber.
Drill for Power (Wire Chase)
A custom service where timber posts are precision-drilled through their core to create internal wiring pathways — allowing electrical wiring to run completely concealed inside the timber. The result is clean, invisible power delivery with no exposed conduit, surface-mounted wiring, or exterior hardware. Wire chases can accommodate lighting, outlets, fans, and other electrical components and are coordinated with the electrical box mortises cut into the post face.
Flashing
Thin metal sheeting — typically aluminum, galvanized steel, or stainless steel — installed at joints, intersections, and transitions between a structure and a building to direct water away from vulnerable connection points. Critical wherever an attached pergola or pavilion meets a home’s wall, roof, or fascia. Improperly installed or missing flashing is one of the most common causes of water infiltration and long-term structural damage at the ledger connection.
Caulking / Sealant
A flexible, weather-resistant compound applied to gaps, joints, and transitions between timber members or between timber and other materials to prevent moisture infiltration. Caulking accommodates the natural movement of wood as it expands and contracts with seasonal moisture changes without cracking or separating. An important part of both initial installation and ongoing maintenance.
Tapered Post
A structural timber post that is wider at the base and gradually narrows toward the top. The taper is cut directly into the timber itself, not applied as a sleeve or casing. The result is a post profile that feels grounded and substantial at its base while reading lighter and more refined as it rises — a visual characteristic common in craftsman, traditional, and architectural timber styles.
Post Sleeve
A decorative timber or composite covering installed around a structural post to provide a clean, finished appearance. A decorative timber or composite covering installed around a structural post. Post sleeves are used in architectural and interior applications where a wrapped or finished look is preferred over an exposed post.
Design Styles
Modern / Minimalist
A timber structure style defined by clean lines, squared posts, consistent spacing, and restrained detailing. The emphasis is on proportion and light control rather than ornament. Modern pergolas work best when post alignment is intentional, beam profiles are simple, and lighting is planned from the start rather than added after installation.
Traditional / Colonial
A design style rooted in architectural symmetry and proportion. Traditional and Colonial pergolas are designed to align with the home’s existing column spacing, trim profiles, and roofline details so the structure feels original to the property rather than added onto it. Common in Craftsman, Colonial Revival, and classic residential settings.
Tuscany
A design style within the Traditional family, characterized by heavier post profiles, round or tapered columns, and decorative beam work that references Italian villa and estate architecture. Tuscany-style pergolas typically feature warm stain tones, arched or curved knee braces, and a sense of substantial presence suited to formal outdoor living spaces and landscaped estate settings.
Rustic / Farmhouse
A timber frame design style that emphasizes natural timber character, heavier post and beam scale, and connection to the surrounding landscape. Rustic and Farmhouse pergolas work best with warm stain tones, visible joinery, and integrated space for climbing plants or garden elements. The goal is a structure that feels like it belongs to the land rather than placed on it.
Mediterranean
A style rooted in warm-climate architecture, oriented around sun control, airflow, and relaxed shade. Mediterranean pergolas are designed for hot sun and moisture exposure, with rafter spacing, roof orientation, and material choices selected for climate performance as much as aesthetics. Arched beams, warm earth-tone finishes, and heavy timber posts are common design elements.
Coastal
A design style built for environments with high humidity, salt air, and intense sun exposure. Coastal pergolas prioritize moisture-resistant species (Cedar, Redwood), corrosion-resistant stainless steel hardware, and roof orientations that maximize airflow and shade. The aesthetic tends toward relaxed, open structures with generous overhangs and lighter finishes that complement waterfront and beachside settings.
Boho-Chic / Eclectic
A design style where the structure itself provides a strong, proportional base for layered textiles, lighting, plants, and furniture that can change over time. The frame is intentionally clean so the accessories define the personality. Warm string lighting, drapes, hanging plants, and integrated power (TimberVolt® Power Post System) are common elements.
Traditional
A design style defined by symmetry, ornamentation, and classic craftsmanship details drawn from American and European architectural conventions. Traditional timber work features raised panel posts, decorative corbels, layered beam assemblies, and joinery details that complement homes built in craftsman, colonial, Georgian, and Victorian architectural traditions. Heavier timber proportions and warm stain tones — Early American, Rich Cordoba — reinforce the sense of heritage and permanence.
Southwest / Desert-Inspired
A desert-inspired design style suited to high-desert, mountain, and sun-rich environments. Southwest-inspired pergolas emphasize open or stepped roof designs that create dramatic light and shadow, natural stone integration, and timber scale that feels grounded against open sky. Thermal mass is a practical advantage in extreme heat — heavy timber absorbs rather than radiates heat, keeping surfaces safe to touch even in high desert conditions.
Asian-Inspired
A design style that references Japanese, Chinese, and broader East Asian outdoor architectural traditions. Key elements include curved or upswept rafter tails, tiered beam profiles, natural or dark stain tones, and restraint in ornament. Asian-inspired pergolas are sometimes referred to as garden pagoda-style structures, though technically they are open-rafter pergolas that borrow the tiered aesthetic and curved profiles of pagoda architecture.
Want inspiration? Browse our custom pergola design ideas for every style of home →
Roofing Materials
Asphalt Shingles
The most common roofing material in North America, made from a fiberglass mat coated with asphalt and topped with mineral granules. They are affordable, widely available, and come in a variety of colors, making them a practical choice for pergolas with a solid roof.
Metal Roofing
A durable roofing material made from steel, aluminum, or copper panels or shingles. Known for its longevity and low maintenance, metal roofing sheds rain and snow efficiently and complements the natural look of a timber frame structure.
Cedar Shake Shingles
Roofing shingles hand-split or sawn from cedar wood, known for their rustic, natural appearance. They provide good insulation and weather resistance and pair beautifully with the warm tones of a timber frame pergola.
Polycarbonate Roofing
A lightweight, translucent plastic panel that allows natural light to filter through while providing protection from rain. A popular choice for pergolas where maintaining an open, airy feel is desired.
Corrugated Roofing
Roofing panels with a wavy or ribbed profile, available in metal or plastic. Lightweight and easy to install, they are a cost-effective option for adding weather protection to a pergola.
Want to go deeper? Explore our guide to roofing types →
Have questions? Talk to one of our timber frame specialists →
Foundation & Footings
Concrete-Filled Sonotubes
A cylindrical cardboard form placed in a dug hole and filled with concrete to create a pier footing. Easy to work with and available in various diameters, making them a popular choice for post and beam and deck foundations.
Footing
The below-grade foundation element that supports each post. Footings transfer the structure’s weight into the ground and must be sized and placed to meet local soil conditions and frost depth requirements. Common footing types include poured concrete piers, concrete-filled sonotubes, and helical piles (also called screw piles or helical piers).
Helical Piles (also called screw piles or helical piers)
Steel shafts with helical plates that are mechanically screwed into the ground to reach stable soil or bedrock. A fast, low-disturbance alternative to poured footings — especially useful on sloped sites, in cold climates, or where excavation is difficult.
Poured Concrete Piers
A common footing type where concrete is poured directly into a dug hole or form to create a solid below-grade support. Cost-effective and widely used for decks, additions, and light structures.
Finishing & Maintenance
Stain
A pigmented finish applied to timber to protect against UV damage, moisture penetration, and biological growth while enhancing or modifying the wood’s natural color. Unlike paint, stain penetrates into the wood fibers rather than sitting on the surface. Exterior stains are available in transparent (shows full grain), semi-transparent (partial grain visibility), and solid (opaque) formulations. We use Sherwin-Williams exterior, UV-rated, water-based stain applied in our shop — every structure receives 2 backrolled coats before shipping, ensuring consistent coverage and factory-quality finish. Touch-up stain is included with every kit. Our standard palette includes 8 colors: Rich Cordoba (most popular — darkest brown), Canyon Grey (currently trending — modern grey), Early American (medium brown), Rich Sequoia (light reddish-brown), Wild Olive (newest — muted olive green), Black, Natural (colorless, shows Douglas Fir), Beach Sand, and Alpine (white — upgrade option at additional cost).
Custom Stain
Custom stain refers to a specially selected or blended finish applied to timber that enhances its natural grain while achieving a specific color, tone, or aesthetic.
⚡ Why This Matters: Because every Western Timber Frame structure is custom, custom stain helps the finish feel just as intentional—whether matching an existing build or creating contrast that sets it apart.
Sealer
A clear or lightly tinted finish that protects wood from moisture penetration without significantly altering its color. Sealers are often applied as a base coat before staining or as a standalone treatment for homeowners who prefer the wood’s natural appearance. Sealers require more frequent reapplication than pigmented stains because they offer less UV protection.
UV Degradation
The breakdown of wood fibers and finish coatings caused by prolonged exposure to ultraviolet radiation from sunlight. UV degradation causes wood to gray, lose its color, and develop surface erosion over time. Pigmented stains and UV-blocking finishes slow this process. Left untreated, UV degradation is primarily a cosmetic issue — it affects appearance long before it compromises structural integrity.
Weathering
The natural aging process of exposed timber as it reacts to sun, rain, temperature changes, and atmospheric conditions. Untreated Cedar and Redwood weather to a silver-gray patina that many homeowners find attractive. Douglas Fir does not weather as gracefully without protective finish and is more prone to surface degradation if left untreated.
Maintenance Cycle
The recommended interval between refinishing treatments (cleaning, sanding, re-staining, or re-sealing). Maintenance cycles vary by species, finish type, climate, sun exposure, and orientation. A south-facing pergola in the Utah desert will need refinishing more frequently than a north-facing structure in a temperate forest. We provide project-specific maintenance schedules with every structure.
End Grain Sealing
The application of a concentrated sealer or finish to the cut ends of timber members — the most porous and vulnerable surface on any piece of wood. End grain absorbs moisture significantly faster than face grain, making unsealed ends a primary entry point for water, decay, and checking. Sealing cut ends at installation is one of the most important and most overlooked steps in long-term timber maintenance.
Spot Repair
The targeted reapplication of stain, sealer, or wood filler to specific areas of a timber structure that show early signs of finish wear, checking, or surface degradation — without refinishing the entire structure. Regular spot repair extends the life of the full finish and prevents localized deterioration from spreading. Part of a proactive maintenance cycle.
Wood Bleach
Bleach is a chemical treatment applied to timber surfaces prior to staining that cleans, neutralizes, and prepares the wood for consistent finish absorption. Removes surface discoloration, tannin bleed, and weathering gray to produce a uniform base across the full timber surface. Applied in the shop as part of WTF’s finishing process before stain is backrolled onto the structure
Design & Configuration Terms
Freestanding
A structure that is self-supporting, not attached to any building. Freestanding pergolas and pavilions require a minimum of four posts and are placed independently in a yard, garden, or poolside area. Because they’re not anchored to the house, freestanding structures must resist lateral loads independently through bracing, post embedment, or engineered footings.
Enclosed Structure (HOA / Zoning Enclosure Compliance)
A timber frame structure — pavilion, gazebo, cabana, or any open-sided design — converted to a fully enclosed building by infilling glass walls, screens, or solid panel systems between the timber posts and roof framing. A common solution when HOA guidelines or municipal zoning requirements restrict open-sided structures but permit fully enclosed buildings, allowing homeowners and commercial clients to achieve the covered outdoor living space they want within the rules that govern their property. WTF provides the complete timber frame package; enclosure systems are sourced and installed separately by the client or a contractor.
Attached (Wall-Mounted)
A structure connected to the home on one side, using a ledger board as one of its two primary support lines. Attached pergolas require fewer posts (minimum two) but place structural loads on the home’s wall framing, which must be properly reinforced. The ledger-to-house connection is the most critical engineering detail in any attached structure.
Shade Coverage / ShadePrint™
The percentage of the area beneath a pergola that is shaded at a given time of day. Shade coverage depends on rafter spacing, purlin density, shade plank width, structure orientation (north-south vs. east-west), and latitude. A pergola designed with tightly spaced 2×6 shade planks provides significantly more coverage than one with widely spaced 2×4 rafters. WTF uses the proprietary term ShadePrint™ to quantify this: the usable shade produced by a structure as the sun passes overhead throughout the day. Standard WTF kits average better than 80% ShadePrint™ — comparable to standing under a large shade tree. This is achieved through higher rafter density and wider shade planks than most competitors, whose structures often produce ShadePrint™ below 40-50% and function primarily as decorative space-definers rather than functional shade producers.
Thermal Mass (Timber vs. Synthetic)
The ability of a material to absorb and store heat energy rather than radiate it. Heavy timber has significant thermal mass — when the sun beats down on a timber post, the wood absorbs and stores that heat within its mass, keeping the surface temperature well below ambient air temperature. Even in 115°F Arizona heat, a timber post remains safe to touch. By contrast, aluminum, metal, vinyl, and other synthetic pergola materials conduct and re-radiate thermal energy, making surfaces dangerously hot in direct sun — potentially causing contact burns. This is a critical safety differentiator for families with children and pets, and a functional contradiction for materials marketed as “shade structures” in hot climates: a material that radiates heat is working against the purpose of the structure it forms.
Overhang
The distance that rafters or beams extend beyond the outermost posts. Overhangs add visual drama, provide additional shade, and protect the post-to-beam connection from direct rainfall. The length of the overhang is limited by the rafter’s ability to resist deflection at the unsupported end.
Bay
The space between two adjacent structural bents or post lines. In a simple four-post pergola, the structure has one bay. In a six-post structure (two rows of three), it has two bays. The number and width of bays determines the overall footprint and the span requirements for the beams.
Pitch (Roof Pitch)
The angle or slope of a roof, expressed as inches of vertical rise per 12 inches of horizontal run. A “6/12 pitch” rises 6 inches for every 12 inches of run. Pitch affects water shedding, snow accumulation, wind resistance, and the visual proportions of the structure. Pergolas with open rafters can be flat or pitched; pavilions with solid roofs require sufficient pitch for water drainage.
Beam Profile
The decorative shape cut into the exposed end of a beam, giving the pergola its distinctive roof silhouette. PergolaScape offers five beam profiles: Axis Step (arrow-like, high/lifted look), Crescent (simple curve, softer look), Crescent Step (curve with added notch for emphasis), Champion (intricate design — most popular), and Roosevelt (smooth upward curve). The beam profile is a style choice and should be matched to the architectural character of the home.
Timber Series (6,000 vs. 8,000)
The designation that determines the thickness and weight class of all timber components in a pergola kit. The 6,000 Series uses slimmer members (6×6 posts, 3×10 beams, 2×8 rafters, 2×4 shade planks) for a lighter, more open aesthetic. The 8,000 Series (most popular) uses heavier members (8×8 posts, 4×12 beams, 3×10 rafters, 2×6 shade planks) for a chunkier, more substantial look with greater shade coverage. In a 14′×22′ pergola, the 6,000 Series weighs approximately 2,925 lbs (886 board feet) while the 8,000 Series weighs approximately 4,561 lbs (1,382 board feet).
Sizing Tiers (Lounge / Family / Entertainment)
The three standard size categories for PergolaScape pergola kits. Lounge size (10′×10′ to 12′×12′) is suited for hot tubs, quiet corners, hammocks, and small patio furniture sets. Family size (12′×14′ to 14′×16′) fits average patios with room for gatherings, BBQs, and poolside shade.
Entertainment size
(16′×16′ and larger) accommodates outdoor parties, outdoor kitchens, bars, and multiple living zones. Note: PergolaScape sizing is based on shade coverage (roof dimensions) — posts are always 12″ in from each corner, so a 10′×10′ roof has an 8′×8′ post footprint.
FullWrap™ Roof
An upgrade option that extends the decorative beam and rafter end profiles to all four sides of the pergola roof, creating visual symmetry from every angle. Standard pergolas show the beam profile on two sides only; FullWrap adds the profile treatment to the remaining two sides for a more finished, showcase appearance.
Teardrop Keystone
A decorative carved wood element shaped like an inverted teardrop, suspended beneath the beams and arch intersections of a pergola. It serves as an ornamental focal point that adds visual weight and elegance to the structure, drawing the eye upward toward the joinery. The rounded, tapered form is a signature design detail in timber frame construction, giving the pergola a finished, craftsman-quality appearance.
Arched Knee Braces (Upgrade)
Curved structural braces installed below the horizontal beams, featuring a keystone cap at the center for a dramatic architectural look. Beyond aesthetics, arched knee braces provide greater structural strength — recommended for high-wind areas or if the homeowner plans to hang swings or hammocks from the structure.
Built-in Bench
A custom timber bench permanently integrated into the structure — attached to posts, beams, or walls rather than freestanding. Built-in benches define seating areas, maximize usable space within the structure’s footprint, and maintain a clean, cohesive timber aesthetic. Always custom-sized and designed to match the species, profile, and finish of the surrounding structure.
Built-in Table
A custom timber table permanently integrated into or built alongside the structure, designed for dining, entertaining, or workspace use. Built-in tables eliminate the need for separate furniture while maintaining a unified timber design throughout the space. Always custom-sized to the structure and use.
Suspended Table
A custom timber table hung from the overhead beam structure by cables, chains, or rods, eliminating the need for legs and creating a floating, architectural centerpiece within the space. Suspended tables are engineered at the beam connection point to handle the dynamic load of an occupied table surface. Hardware, cable, and mounting systems are selected to complement the timber finish and style of the surrounding structure.
Built-in Counter
A custom timber counter surface integrated into the structure — typically associated with outdoor kitchen areas, bar setups, or serving stations. Provides a durable, weather-resistant work surface that is part of the timber structure itself rather than a separate appliance or fixture. Always custom-sized and species-matched to the surrounding structure.
Built-in Cabinets
Storage or display cabinets that are permanently integrated into the structure of a pergola, pavilion, or outdoor living space rather than freestanding. Built-ins are custom designed to fit the specific dimensions and style of the structure, creating a seamless, finished look. Common uses include outdoor kitchen storage, bar areas, equipment housing, and decorative shelving. Because they are part of the structure itself, built-in cabinets should be specified during the design phase rather than added after installation.
Custom Profile
A decorative shape or silhouette cut into the exposed face or end of a timber member — beams, rafters, posts, corbels, brackets, or fascia — that gives the structure its distinctive architectural character. Custom profiles are designed to complement the style of the home and can range from simple chamfers and curves to elaborate multi-step and sculptural designs. Every WTF profile is cut with CNC precision for consistency across all matching members.
Custom Knee Brace
A diagonal timber brace connecting a post to a beam, cut into a decorative profile specific to the design of the structure. Unlike standard straight or simple curved knee braces, custom profiles — scrollwork, compound curves, stepped designs — are CNC-precision cut to match the architectural character of the surrounding timber work. Structural and decorative simultaneously.
Process & Buying Terms
Design Consultation
The initial conversation between the homeowner and the design team to establish project goals, review site conditions, select materials, determine size and configuration, and develop a preliminary scope and budget. A good design consultation covers aesthetics, engineering constraints, permitting requirements, and timeline — not just price.
Site Survey
An on-site visit (in person or virtual) to assess the installation location, measure the footprint, evaluate soil conditions, document the home’s architecture (roofline, fascia details, wall construction), and identify any site-specific challenges (slope, access, utilities, setbacks). Site surveys inform the engineering and ensure the structure fits the home — not the other way around.
Lead Time
The time between order confirmation and delivery of the finished structure. Lead times for custom timber pergolas vary based on design complexity, species availability, and production schedule. Lead time is not the same as installation time — it’s the fabrication and shipping period before installation begins.
Kit vs. Custom
A kit pergola is pre-designed and mass-produced in standard sizes and configurations, shipped in boxes or on pallets, and assembled on-site using the included hardware and instructions. A custom pergola is designed to the specific dimensions, species, timber profile, configuration, and architectural details of the homeowner’s project, fabricated as a one-of-one package, and shipped on freight trucks. The cost, quality, and experience are fundamentally different.
Freight Shipping
The transportation method used for heavy timber structures — typically flatbed trucks with forklift or crane offloading. Unlike kit pergolas that ship via parcel carriers in cardboard boxes, custom heavy timber packages require industrial logistics. Freight shipping adds cost but is necessary because the individual timbers are too large and heavy for standard parcel delivery.
Turnkey Installation
A project delivery model where the pergola company handles everything from design through installation — engineering, permitting, fabrication, shipping, and on-site assembly. The homeowner receives a finished structure without coordinating separate contractors. Not all pergola companies offer turnkey service; many sell kits or materials only and leave installation to the homeowner or a local contractor.
Permit
Official approval from a local building department authorizing construction. Most jurisdictions require permits for outdoor structures above a certain size, and nearly all require permits for structures attached to the home. The permit process typically requires stamped structural drawings, a site plan showing setbacks, and an application reviewed by the building department. Building without a required permit can result in fines, required demolition, or complications at resale.
Change Order
A formal, written modification to the original project scope, design, or budget — signed by both the client and WTF — that documents any additions, deletions, or substitutions after the initial contract is executed. Change orders protect both parties by ensuring scope changes are agreed upon and priced before work proceeds. Verbal change requests are not change orders.
Submittal
Documentation — shop drawings, product data, material specifications, or engineering calculations — provided to a building department, architect, or general contractor for review and approval prior to fabrication or installation. Submittals confirm that the proposed materials and methods meet the project requirements and applicable codes. In commercial and large-scale projects, the submittal process is a formal part of the construction workflow.
3D Rendering
A computer-generated visual representation of the proposed timber structure shown in three dimensions, allowing the homeowner to see how the finished project will look in context before fabrication begins. 3D renderings help clients visualize scale, proportion, profile details, stain color, and integration with the home’s architecture. A standard part of WTF’s design process for custom projects.
Architectural Drawings
Detailed scaled drawings showing the dimensions, layout, elevations, and construction details of the proposed structure. Architectural drawings communicate the design intent to engineers, contractors, and building departments and serve as the basis for stamped structural drawings when permitting is required. Distinct from 3D renderings — architectural drawings are technical documents, not visual presentations.
HOA (Homeowners Association)
A governing body that enforces community building standards within a subdivision or planned community. Many HOAs require written approval of outdoor structure plans before a permit is applied for. HOA approval and municipal permit approval are two separate processes — both may be required.
CC&Rs (Covenants, Conditions & Restrictions)
The legal document containing an HOA’s specific building rules — approved materials, color restrictions, size limits, and placement requirements. Reviewing CC&Rs before finalizing a design prevents costly changes if the structure doesn’t meet community standards.
Tools of the Trade
Tools & Hardware Provided
Knife Plates
Steel connector plates with a flat base and protruding blade that embed into the timber, used to connect and secure timber frame joints
Hex Bit
A screwdriver bit with a six-sided tip that fits into hex-head fasteners, used with a drill to drive hardware during assembly
Wedge Anchors
Heavy-duty expansion bolts that wedge tightly into drilled concrete holes, used to secure posts or hardware to a concrete surface
Spade Bit
A flat, paddle-shaped drill bit with a sharp center point, used to bore large clean holes through wood
1/4″ Bit Adapter
A small chuck attachment that converts a drill to accept standard 1/4″ hex shank bits
Caulk (For Solid Stains)
A textured, flexible sealant designed for wood surfaces, used to fill gaps and protect against moisture penetration
5/16″ Wood Lags
Large, heavy-duty threaded screws used to fasten substantial timber components together with strong holding powerLarge, heavy-duty threaded screws used to fasten substantial timber components together with strong holding power
3″ Wood Screws
Standard threaded fasteners used to secure framing components throughout the structure
1 Gal. Touch Up
A matching paint or stain used to cover scratches or marks made on the timber during installation
1″ Dowels
Short, cylindrical wooden pegs used to align and secure timber connections during assembly
Tools Not Provided
Ladders
A portable, freestanding climbing structure used to safely work at elevated heights; ladder height should account for beam height plus safe working clearance
1/2″ Concrete Bit
A hardened masonry drill bit designed to cut through concrete, used to bore anchor holes into concrete footings
Leveling Instruments
Tools used to confirm that surfaces and structures are perfectly horizontal or vertical; a laser level projects a beam across a large area for fast, accurate readings and is strongly recommended, though a standard bubble level works as well
Drill & Hammer Drill
A drill is a handheld power tool that drives screws and bores holes; a hammer drill adds a rapid hammering action that allows it to penetrate hard materials like concrete — both are needed for this installation
Measuring Tape
A flexible, retractable metal ruler used to ensure accurate layout, spacing, and dimensions throughout the build
Temporary Bracing
Lengths of lumber, typically 2x4s, used to prop and hold posts in a plumb (perfectly vertical) position while the structure is being assembled
Optional Tools Not Provided
Air Compressor
A powered machine that pressurizes air and stores it in a tank, then releases it to drive pneumatic tools such as nail guns, brad nailers, and staplers. Essential for timber frame and pergola assembly, where pneumatic nailers are used to fasten decking, trim, and other components quickly and consistently. Compressors are rated by PSI (pounds per square inch) and CFM (cubic feet per minute) — the tool being used determines the minimum requirements needed. For most pergola and pavilion kit assembly, a portable pancake or hot dog compressor is sufficient.
Chain Saw / Reciprocating Saw
A chain saw uses a rotating chain of cutting teeth for heavy timber cuts; a reciprocating saw uses a back-and-forth blade for more controlled cutting in tight spaces — either may be necessary for trimming post bottoms to level the structure on a sloping surface
Staple Gun
Staple gun, which drives staples rapidly into material; only required if roofing material is being added to the structure
This glossary is maintained by Western Timber Frame — 16 years, 7,000+ structures, all 50 states. If you encounter a term we haven’t covered, contact us and we’ll add it.
Last updated: April 2026
