How to Build a Pergola

How to Build a Pergola


Pick the Site

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Pergolas can add a graceful style and architectural character to your home or garden. They come in a large variety of sizes and styles. This project measures 6 feet tall and 8 feet wide on each side and uses long-lasting pressure-treated 4x4 rafters.

As you choose your area, keep in mind that a standard 6' x 8' pergola has overhangs that extend eighteen to twenty inches beyond that, so plan accordingly if you choose to build close to your house.

Pick a flat, level area to build your structure. If you don’t have a flat, level area, then grade the desired area by removing soil and hand tamping to level. Remember to save the soil to use as fill throughout your yard or beds.

Also, consider locating your pergola near shade trees, especially to protect you from late-afternoon summer sun. A common mistake is to think that a pergola is a shade structure; the reality is that the overhead network of beams and rafters affords very little shade. They’re best used as a focal point and setting for socializing or quiet relaxation.

Step 1

Dig Post Holes

Dig Post Holes

Dig the Post Holes

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When you've set your location, call your local utility and cable companies and have them mark the location of any underground services. Once they have confirmed there are no underground lines in your future pergola location, begin digging the post holes.

Mark those post locations with stakes. Then verify that the layout is correct by measuring diagonally from corner to corner on both sides. The measurements should be identical; so adjust as necessary.

In this project, our pergola will be built at the corners of an existing retaining wall; however, the pergola build process is the same with or without the wall in the design.

To dig the post holes, you can use a clamshell digger, power auger or a shovel. Your local building codes should specify a recommended depth for post holes in your area. For an 8-foot tall structure like this one, plan on about two-feet in depth. The depth of your hole should be about 1/4 of the height of your post.

For a 6x6 post, the diameter of the holes should be about 12 inches square. As a rule the width of your post hole should never be less than 10 inches. You want holes deep and wide enough to easily support a standard 4x4 post.

Step 2

Set the Posts

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Once the post holes are dug, set the posts. Place the 6x6 post into the hole. Remember to check that the post is plumb using a three foot level, as you go (image 1 below).

Brace the post with stakes. To do this, attach a 1x4 to the side of the post with a single nail or drive screw. When you're satisfied, secure the free end of the brace to a stake driven into the ground. Set another brace at 90 degrees to the first. Secure with nails. Continue this process to set the three remaining posts.

Prepare the ready-mix concrete and fill the holes. You'll need roughly four bags for each hole. In a wheelbarrow, pour the ready-mix powder and slowly add water, mixing while you go. You'll need roughly six gallons of water to one 40-pound bag. But be careful not to use too much water, it could weaken the concrete. The consistency should be like peanut butter. When the concrete is ready, fill the hole to within an inch of the surface. This allows the concrete to expand and contract with weather changes.

As you fill, use a broom handle, or shovel to "churn" the concrete to ensure that there are no air pockets (image 2). If there are, you may need to add more concrete to bring the level to within an inch of the surface.

Let the concrete set for 48 hours.

Step 3

Cut Decorative Ends on Beams

Cut Decorative Ends on Beams

Prepare Support Beams and Rafters

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While the concrete footers are setting, prepare the support beams and rafters for installation. The support beams attach to the posts and carry the load of the structure. You will need two to four beams on each side.

The rafters attach atop the support beams. In this project we are using nine rafters as the roof.

It's a good idea to buy the beams and rafters precut to the size you need, so the only cuts you'll need to make will be at the decorative ends of the beams and rafters. We cut a 45-degree angle on the bottom end of each one.

Step 4

Install Beams and Rafters

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After the concrete in the post holes has set, and the beams and rafters are cut, cut the tops of the posts to an even height. For our 8-foot tall pergola we cut our posts to measure 7-1/2 feet from the ground. The rafters on top will eventually add another six inches to the height (image 1 below).

Measure, mark then cut the tops with a circular saw. As you cut each post, you can use a 2x4 and a level to make sure all the posts are the exact same height.

Install the beams. Each beam is two 2x8s fastened together on either side of a post - an inner and outer beam. Begin by resting the first 2x8 beam on-center over a pair of posts to make sure the overhangs are of equal length. Measure each as you go along (image 2).

Secure each end of the beams to the top outside face of each post with two 4-inch screws to temporarily hold them in place. Attach the rest of the beams in the same way.

All that's left is to install the rafters and to permanently secure the beams in place with the bolts. Lay out the rafter locations on the tops of the beams at one-foot intervals.

Take time to measure the overhang of each rafter carefully to keep the whole set in alignment (image 3). Install the rafters by fastening each in place with two 5-inch galvanized drive screws at each end.

With everything in perfect alignment and centered you now can permanently secure the beams to the posts using 8-inch galvanized bolts. Using a 1/2-inch drill bit, drill a top and bottom pilot hole centered on each post. Use a hammer or rubber mallet to pound the bolts through the beams and post. Finally secure them using a 1/2-inch nut on the inside of the structure.