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How To Build a Three Post Pergola

Building your own three post pergola, also known as a corner pergola, can be incredibly rewarding. Although the process is fairly straightforward, you will be working with angles throughout the project. A three-post pergola is no more difficult to construct than the more common four-post version, but you will need to be familiar with framing, or speed square.

What Can I Build?

There are no design limitations when building your own three post pergola from scratch. Typically, these are built in an unused corner of the yard to conserve space. If possible, you may want to select a spot that enhances the experience of using the pergola, such as one that faces a sunset.

Backyard Discovery 2006539 Laguna Cabana Pergola with Conversation Seating, Cedar and Indigo

In a three-post pergola, one side will be longer than the other two, so make sure your longest side does not exceed the lumber available. Your local codes official can tell you if your lumber will support your design. If your design has large spans, expect to use larger lumber to support the load.

Tools You May Need to Build Your Pergola

You will need a few carpentry tools, as well as safety gear. Below is a list of common tools required for this project, but your design may require others as well:

  • Circular saw
  • Ladder
  • Bar clamps
  • Drill with both wood and masonry bits
  • Level
  • Carpenter’s square or speed square
  • Nylon string 
  • Shovel and post hole digger
  • Wheelbarrow, mixing pan, or large bucket
  • Handsaw or reciprocating saw
  • Jigsaw (if your design includes curves)
  • Hammer
  • Tape measure
  • Pencil or marker
  • Wood chisel
  • Socket set or wrench

Steps to Build a Three Post Pergola

Safety First

As with any home improvement project, avoiding injury is the most important step you can take. Make sure that you have eye and ear protection, gloves, and any other safety gear you feel is necessary. Also consider having help readily available.

Step 1. Location

As mentioned earlier, the location of your pergola is important. Some jurisdictions will require a permit, while others may not. Find out where your lot lines are and stay at least 6” inside them. Also, consult your architectural committee if you live in a restricted subdivision, as some may prohibit any outdoor additions.

Step 2. Layout

When you have your location selected and your required approvals (if needed), you can begin to lay out your pergola. A three post pergola is really just a right triangle. Some designs incorporate a fan design for the roof, taking full advantage of the triangular shape. If you recall from school, a right triangle will have one 90-degree angle and two 45 degree angles, with one side being longer than the other two. To begin, mark the two short sides along the ground and pull a string between these two points. This will indicate potential obstructions, like a fire pit. 

Pro Tip. If you are unfamiliar with your lot, contact your local utility company and have them mark any underground obstructions. 

Step 3. Foundation

After you have your footprint, you’ll need to locate where your posts will be attached to the ground. This is done by starting in the 90 degree corner and measuring outward to each 45 degree corner. These will be the locations of your post holes. The size of the hole will be determined by the size of your post, so the rule is to make the diameter of your hole twice as large as the post. For example, an 6” x 6” post will need a 12” diameter hole. The depth of the hole will be determined by the frost line in your area, so check with your local codes official.

After your holes are dug, you are ready for concrete. Place an appropriate sized concrete form into the hole, level with the ground. Now, mix your concrete and fill the form to the top. A smooth finish will allow your post to sit firmly. Repeat for the other two corners. If your lot slopes, using a laser level is recommended to keep the three piers close to the same height.

Step 4. Install The Posts

The modern way to attach your posts to the concrete is with specially designed hardware connectors. You can find these at any home improvement retailer. These simply bolt to the concrete, and your posts are then bolted to the connector. This eliminates many of the issues associated with simply pouring concrete around your post.

Before installing your posts, you’ll want to build some bracing. This is done by driving a short, sharpened 2” x 4” into the ground and attaching another full length 2” x 4” to it at a 45-degree angle, allowing it to pivot. Do this in each corner, in both directions. Using your level, plumb the post in one direction and attach one brace to the adjacent side using a nail. Then, plumb the post in the other direction and repeat the action for all three posts.

Step 5. Set The Beams

Connecting the beams to the post is done by drilling pilot holes all the way through the beam and post and driving a weather-resistant carriage bolt into the hole. Secure it with a flat washer, lock washer, and nut. Repeat this process on the other sides.

Step 6. Set The Corner Braces and Rafters

After the beams and braces are in place, it is time for the rafters. Your design may include corner braces. In a three-post design, this will require a compound miter cut. We recommend a miter saw for this task, but the job can be done using common tools. After the braces are installed, you can set the rafters.

The rafters will get most of the attention, so extra time making them attractive is time well spent. Some owners will cut decorative curves or angles into the ends for appearance. If you plan to do the same, make the cuts while the rafters are still on the ground.

Attach your rafters with weather-resistant screws, spacing them evenly. If your design will have louvers, install them on top of the rafters. As louvers are usually thin material, be cautious when installing them to avoid splitting.

A Beautiful Addition to Any Yard

Your own three-post pergola is a great place to sit and relax. Enjoy your evening sunsets and morning coffee in peace and solitude. However, knowing you built it yourself may be the best part of all.

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