Completed 12x20 timber frame pergola kit installed over a concrete patio with rich wood stain and decorative beam detailing

Planning a 12′ × 20′ Timber Frame Oversize DIY Pergola

A 12′ × 20′ oversize timber frame pergola is a popular size for backyard entertaining. The 12′ × 20′ is the roof size; the footprint, post to post, is usually about 10′ × 18′. A typical kit includes four 8″ × 8″ posts, 4″ × 12″ beams, 3″ × 10″ rafters, 2″ × 6″ shade planks, and knife plates, all pre-cut and numbered so two people can raise it.

Dark 12 by 20 foot oversize timber pergola shading a backyard patio with lounge chairs and a grill beside a stucco home
A 12′ × 20′ oversize pergola over a patio.

Key Takeaways

  • Roof vs. footprint: 12′ × 20′ roof, about 10′ × 18′ post to post
  • Timbers: true-to-size 8″ posts and 4″ × 12″ beams
  • Easy layout: notched beams and drop-in rafters
  • Two people: pre-cut, numbered joints, no cutting on site

How Is a 12′ × 20′ Pergola Kit Designed?

Every kit is designed for its own space and the way the family wants to use it, so no two are exactly alike. The design team works with you on the size, height, style, and budget. The dimensions below are a typical starting point, and they can change to fit your yard.

Freestanding 12 by 20 foot timber pergola in Rich Sequoia stain over a concrete pad in a park-like backyard
A freestanding 12′ × 20′ in Rich Sequoia.

What Comes in a 12′ × 20′ Pergola Kit?

Labeled diagram of a 12 by 20 foot pergola kit showing the posts, beams, rafters, shade planks, braces, and knife plates
The parts of a 12′ × 20′ kit.
LabelPartThicknessWidthLengthQty
APost8″8″110″4
BNotched support beam4″12″202″2
CSupport beam4″12″106″2
DRafter3″10″144″12
EShade plank2″6″240″13
FKnee brace3″8″36″8
GBeam extension4″12″13″4
HBeam extension4″12″13″4
IKnife plate1/4″7″7″4

How Does the Drop-In Rafter Layout Work?

The support beams arrive already marked and notched for every rafter, so you never measure or work out the spacing. The rafters simply drop into their slots. Every joint is cut and numbered in the shop, and the timbers are true-to-size, so even an oversize kit can go up in as little as one Saturday afternoon. Each joint uses The Dovetail Difference®, a patented mortise and tenon dovetail joint (U.S. Patent 9,797,149 B2), and the posts anchor on EarthAnchor™ knife plates.

Craftsman in the shop carefully cutting joinery into a large timber before the pergola kit is test-fit and shipped
Joinery cut in the shop.
Dark timber pergola built over a raised second-story deck with railings on the back of a tan stucco home
A 12′ × 20′ over a raised deck.

Questions About 12′ × 20′ Pergola Kits

What size is a 12′ × 20′ pergola footprint?

The roof is 12′ × 20′. The footprint, measured post to post, is usually about 10′ × 18′, because the roof extends past the posts. Exact dimensions are set by your design.

How many people does it take to install a 12′ × 20′ kit?

Two people can raise it. Every joint is pre-cut and numbered in the shop, so there is no measuring or cutting on site.

How long does it take to install?

Many oversize kits go up in as little as one Saturday afternoon.

What is a drop-in rafter layout?

The support beams arrive notched for each rafter, so the rafters drop into place at the right spacing without measuring.

Are the timbers full size?

Yes. The timbers are true-to-size, so an 8″ × 8″ post measures a full 8″ × 8″.

Western Timber Frame has designed, handcrafted, and delivered more than 7,000 outdoor structures in all 50 states since 2008. See timber pergola kits, or request a free design consultation and call 877-870-8755.

Western Timber Frame™ — Payson, Utah | Since 2008 | 7,000+ structures in all 50 states
2026 SBA Manufacturing Award | HGTV Design Excellence Award | 28 Best of State Awards

Good Projects Start With Good Questions

Whether you are still exploring ideas or already planning your project, our team can help you understand what is possible for your space. Over 7,000 finished structures sit behind that conversation, since Western Timber Frame designs each one around how the space gets used.

Let’s Talk About Your Project

(877) 870-8755

Content Writer, Architectural Photographer & Outdoor Living Author, Western Timber Frame

Marilynn Thompson is a content writer, architectural photographer, and outdoor living author at Western Timber Frame™, where she specializes in custom timber pergolas, pavilions, gazebos, and heavy timber construction. Since joining the company, she has helped document thousands of custom projects through technical research, homeowner interviews, jobsite photography, and educational articles that explain complex building concepts in clear, practical language.

Her work combines engineering research with real-world project experience, covering topics such as structural design, building permits, installation, timber species, joinery, maintenance, and outdoor living design. She regularly collaborates with Western Timber Frame's designers, engineers, and project specialists to ensure every article reflects current building practices and accurate technical information.

As the company's architectural photographer, Marilynn has photographed custom timber structures across the United States, documenting how they perform in different climates, landscapes, and architectural styles. Her writing is informed not only by research, but by conversations with homeowners and business owners who have lived with these structures for years.

Her goal is simple: to help homeowners understand the decisions behind a custom timber structure so they can build with confidence, not guesswork.

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