pagoda pergola red tiered roof

A concrete foundation, deck or footings give a structure or building a strong base to build upon. Completing the foundation correctly is one of the most critical aspects to the durability of your entire project. Along with established support it provides a level platform, as well as spreading out the weight of a structure.

electric power line markings

Call Early & Plan Before

Water, electric, natural gas, phone cable, and T.V. lines run underground. Call 811, the utility-locate hotline, a few days before you plan to break ground, or you can also make an online request. A service agent will give you a ticket number and tell you within an approximate time frame a utility worker will come and mark with paint or put up flags.

Once the buried lines have been marked, dig carefully around and if the project is close to buried utilities, consider revising or relocating your project so you do not unintentionally harm yourself or an underground utility line.

Footings for Pergolas Larger than Your Concrete Pad

If you’re fortunate enough to have an established concrete pad, you may be well on your way to an outdoor living cover. Below is information for weight on a concrete pad.

Depending upon your design and layout some timber frame shade shelters may use both a concrete pad and one or more footings — as shown with the timber frame DIY pergola kit pictured here:

#DIYPergolaKit

Regardless of what type of timber shade shelter you plan to install, the footings provide a sound base and must be the correct width and depth to provide ample support. The type of soil will also influence variations in depth and footing design.

What is Your Frost Line?

When excavating for your deck, arbor, gazebo, pavilion, pergola or trellis footings, you must dig below the frost line.

Our frost line depth map will give you a rough estimate of what your frost line may be. Use your address and zip code and check with your local building codes before you begin to dig.

For construction purposes, the frost line is simply the deepest point within the ground at which the earth will freeze and thaw. The remitting of freezing and thawing over time could cause uneven settling of the foundation as can be witnessed in the famous bell tower of Pisa. The leaning tower of Pisa took 200 years to build and five years after its completion it began to lean as a result of soft ground settling.

Protect Your Lawn

The digging process brings up a lot of rocks and soil that is better not to have on the grass. Place a wheelbarrow or a tarp on the ground outside of the the area you have marked out for your deck or shade shelter. Putting the excavated contents of the hole place the excavated soil from the footing hole on a nearby tarp or in a wheelbarrow lets you easily move it out of the way when you have finished the dig.

Kinds of tools Useful for Digging Footing Holes

A hand shovel is great for digging a couple holes but if you have several holes to dig, a motorized auger (available for rent at your local home center) can make the job easier. Also available are 2-person machines. If you have several holes, renting a skid-steer loader with an attached auger is something to consider. Otherwise, a manual clamshell digger, which is slower but equally effective, especially if if the soil is rocky. Another nice tool is the pry bar. A pry bar is useful for prying up rocks and tamping in the dirt around the posts.

Width of Footings

The width of a footing is fixed upon the load-bearing capacity (LBVs) of the soil. Or in other words, the assumed maximum weight the ground or rocks are able to bear up. Under building codes the width of a footing will vary according to the location, conditions and structure. Unprepared fill, organic silt, clay or peat should not be assumed to have “presumptive” load-bearing capacity without submitted substantiated data proving the classification,, strength, and compression of the soil.

In general, a one-story building will need a minimum of a 12-inch wide footings on undisturbed soil with LBVs between 1,500 and 4,000. For a two-story building, the footing should be a minimum of 15-inches wide.

#2-StoryPergolaKit #PrivacyWalls

How to Shape a Footing Hole Dig

bell shaped footing for decks and pergola
dig footing hole concrete bell shaped form

A bell-shaped footing, sometimes called a spread base footing widens at the base the footing. Bell-shaped footings use the natural laws of physics to solidly secure to the earth, evenly distributing the load weight.

A bell-shaped footing, sometimes called a spread base footing widens at the base the footing. Bell-shaped footings use the natural laws of physics to solidly secure to the earth, evenly distributing the load weight.

Load-Bearing Pressure

Footings provide a level platform for forms or masonry as well as spreading out the weight of a structure. The soil matters, and plays a vital role in carrying the load with foundation footings. Here is how to make the sure the soil will carry the load. The soil directly beneath the footing will bear the greatest load and should be thoroughly compacted for this reason.

footings diminishing load pressure in soil

You can get a decent idea of compression soil strength —directly under the footing area— with the use of a hand Penetrometer. A Penetrometer is a spring-loaded, pocket-sized device the estimates the pressure soil bear. It is calibrated to give readings in tons per square foot.

Naturally Rot-Resistant

Your ShadeScape® DIY deck, gazebo, pavilion, pergola, or trellis kit will come beautifully pre-stained, ready to install. NEVER coat the post with roofing tar or paint attempting to keep moisture out. Painting it or coating it with roofing tar will NOT extend the life of the timber post. It will hold in extra moisture that will not allow the wood to breathe.

All ShadeScape® timber comes from heartwood, the interior portion of a tree because it is rot-resistant. Pressure-treated timber and cedar are naturally rot-resistant and if allowed to ventilate properly, it will naturally whisk away moisture when exposed to air.

There are some projects or conditions for which we do install a moisture barrier over pressure treated timber posts that are rated for “ground contact.” The base of the posts must be installed to protect from an on-going damp environment.

Moisture

Wood is a living, breathing material. When the humidity (the amount of water vapor dissolved in the air) is high wood will lose some of its moisture. Or when the atmosphere is dry, it will capture some of the water from the air. The movement of moisture in and out of the wood is the process called “breathing.” As the timbers expand and contract it acclimatizes to its new environment

During the warmer seasons, if wood is within an enclosed room and is not sufficiently damp the dry room air will steal moisture from the wood. Much like excessively dry skin is less elastic, or papery, likewise wood becomes brittle when deprived of moisture. Even with decent ventilation bringing fresh oxygen into a room, it will not bring the needed level of moisture. It will in fact, do the opposite. This is because the outside air during the colder seasons cannot absorb or transport needed moisture, making the climate indoors extra dry. With high humidity, damp wood loses moisture and dry wood will capture moisture from the air.

timber bridge with piers in wind storm

Built in 1872, the Ventura Pier located on the Pacific Ocean in California was once used as a commercial wharf. It is the oldest pier in California and is still enjoyed as a pedestrian walkway and for fishing.

Moisture is not the enemy to wood and will not decay simply because it is wet. It takes rather special conditions of moisture, temperature (the optimal being between 70°F to 85°F), air and food for wood destroying organisms to survive. Several historical structures prove the longevity of timber exposed to excessive moisture, especially found in bridges, decks, and piers.  One fine example is in the U Bein Bridge of Myanmar. Built in 1850, the U Bein Bridge has over 1,000 timber pillars standing in water and stretching up out of the lake.

Deck with attached footings

Protection at the Base of the Post

The place where a post is most vulnerable is at the base where soil or moisture comes in contact with the wood. Water can seep into the tiny gap between the post and concrete and sit in there like a pool. This is why building codes require concrete to be crowned (slightly sloped) away from so water will flow away.

Steel escalates the tensile strength of concrete and footings. A quality concrete has anywhere between 3500 to 4000 pounds per square inch (PSI) of strength to resist tension failure. Rebar a minimum of 40,000 PSI of tensile strength.

Footings require a 1/2″ 3 ring rebar. The concrete must be a minimum of 2″ thick between the rebar and the side surface. The top of the footing must be a minimum of three inches above ground.

The Seven Foot Rule of Thumb

Transits and lasers are used by pros to measure the pitch of a sloped grade.

Note: The seven foot rule is simple measure that is easy to remember. This means the widest point of the underside of the footing is no closer than seven feet from the slope. Or what some call “daylight” because if you picture an imaginary horizontal tunnel it would be seven plus feet before you hit daylight.

In most conditions it is on the conservative side. However, every slope should be examined and understood. For example, a site that receives a lot of rain or heavy snow or has leda or quick clay, it is necessary to seek out a professional before any building commences.

Seven foot rule plan for footings

How to Build a Deck on Sloped or Uneven Ground

As hillsides are subject to the surface soil inching downhill and landslides. The foundation footings must be stepped if the slope is greater than 1’ vertical within in a 10′ horizontal. On some projects, a step or an “L” or shaped footing may be best.

l-shaped footing on sloped hillside for deck

L-Shape Footings

An L-shaped footing is normally used in a single load application on the heel side of the slope and only on cases where there is a benefit from extending the toe. The main factor would be soil bearing allowance verses applied pressure. While the soil conditions and load are key in the design, “site conditions” contribute also in the decision on footing shape.

For example, if there are existing services which are not practical or economical or there are site constraints such as imposed by limits of space, an L-shaped footing may in some situations be installed.

Mix Concrete

How much load bearing capacity a concrete block can hold is determined by a number of factors such as how compact the soil is, the concrete mix, the age, (the hydration and hardening process of concrete causes it to become stronger over time), the size, shape and structural content all have to be taken into consideration.

Be sure the mix of concrete is the right strength and the best consistency every time. Too little water and the mix won’t stick together while too much water weakens the concrete. Mix enough concrete to fill each hole. With a level, make sure the top of the footing is level.

Can My Concrete Pad Hold A Timber Frame Pergola?

How much load bearing capacity a concrete block can hold is determined by a number of factors such as how compact the soil is, the concrete mix, the age, (the hydration and hardening process of concrete causes it to become stronger over time), the size, shape and structural content all have to be taken into consideration. If you already have an established concrete foundation, have your pad inspected by a professional before installing a timber frame DIY arbor, gazebo, pavilion, pergola, or trellis. If you are still concerned with whether or not it can hold these heavy timber frame structures, here is what you should know:

elephant in high heel shoeFor example, the weight that is brought to bear upon a concentrated point or when it is distributed over a wider area. A block that is used to support an individual column will bear less weight than a load distributed across a network of support from other load bearing units or columns. When weight is uniformly distributed it requires twice as much weight to break it as it would were the weight concentrated at the center.

new car parked on concrete padConcrete is measured for strength in PSI meaning pounds per square inch of pressure that it can bear. A typical residential patio is 4″ thick with an average of 3000 pounds per square inch ratio. It is designed to carry more than the weight of two automobiles. The average compact car is about 3,000 to 3,500 lbs. A mid size car, van or light truck is about 5,000 to 7,000 lbs. A full size truck is 7,000 to 12,000 lbs.

four men stand on concreteTwo automobiles covering the same amount of space far outweigh an oversized heavy duty timber frame pergola. The overall total weight of an oversized pergola is nearly 4,000 lbs. which would compute to be around 1,000 lbs. of undistributed weight for each beam. Simulating this would be like placing 4 extra large sized men standing on one corner. After the weight is uniformly distributed between three other beams the PSI is considerably less.

contemporary style pavilion

With footings, a concrete slab or pavers can be installed beneath the pergola or gazebo at a later date or to budget your projects in steps.

Get the Free Ultimate Pergola and Pavilion Guide

Get the Free Ultimate Pergola and Pavilion Guide

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