Building a Pergola on a Deck

What You'll Need
15 pounds- 2 1/2" galvanized screws
8- 6"x1/2" carriage bolts
8- 7"x1/2" carriage bolts
4- 4"x4"x10' cedar posts
4- 2"x8"x10' cedar boards
5- 2"x6"x10' cedar boards
6- 2"x6"x8' cedar boards
Chalk line or laser level
Tape measure
Jig saw
Electric drill and associated drill bits
Nails for setting marks
Spirit level
Circular saw
Ratchet and socket

The simplistic design and square shape of a pergola makes it a simple project to build for the average do it yourselfer. If you have access to average wood working tools, have a deck that is raised high enough so that you can get beneath it, then this project may be one you wish to consider. The premise behind this project is to cut holes in the decking and place the upright beams through them. They can then be fastened to the joist beneath. Add some simple wooden edging, and you have a custom made pergola. Here, we discuss this project, materials needed, and construction tips.

Setting your Design

This design assumes you have a raised deck, and enough area to get the height needed. You should plan on the upright standards being 9 feet, as we will use 10 foot 4" X 4" cedar posts for construction. The pergola will be 8' square with 4x4 cedar posts, doubled 2x8 beams, and use battens for mounting a sunshade. The plan is based on one of the many blueprints available on the internet.

You first should check with local authorities to determine if there are any building codes you need to follow. You might also need a permit.

Let's build It

To help simplify the process, I have added some 3D illustrations, which will be referenced throughout the guidelines.

Begin by laying out your 8' by 8' area. This will be measured from outside of each post to outside of adjacent post, and will be measured from inside edge of the joist. It is very important to "measure twice, cut once" here to avoid damage to the deck. We are assuming that the deck has 2x8 joists 16" on center.

Making the Measurements

1. Determine the inside edge of the joist as a starting point, and mark. 2. Measure 8' along this joist, making another mark. 3. Snap a chalk line between these 2 points. 4. Drive a 6D nail halfway in at the mark, and use as a measuring point for other legs of 8' square. See illustration #1. A highly accurate method of making these measurements can be found on the web.

Making The Cuts

1. From your starting point, use a short length of 4 X 4 to lay out post hole on deck. 2. Cut 4 X 4 hole in decking. See illustration #2. 3. With the aid of a helper, stand the post on end, and carefully place in 4 X 4 hole. 4. Drill 2 1/2" offsets holes through the post and joist. 5. Secure the post with the 6" carriage bolts. See illustration #3. The offset helps maintain structural integrity. 6. Repeat for remaining 3 posts. 7. Measure each post 8.5 feet from deck, and cut each at this mark.

Attaching the Cross Beams

1. Align (2) 2"x8"x10 boards, and screw them together, working from both sides to insure that they don't buckle. 2. Repeat for other side. 3. Attach to 4 X4 cedar posts, using 7"x1/2" carriage bolts. See illustration #4. Allow an overhang of each cross beam to be equal on each end. 4. These cross beams may be given a more detailed design by routing the ends. See illustration #5.

Attaching the Rafters

The (5) 2"x6"x10' cedar boards will be place equidistant on the pergola.

  1. Find center of board.
  2. Mark each end, allowing for overhang. Mark both sides of board from center.
  3. Fasten rafters to cross beams with 2 1/2" galvanized screws.

When completed, your pergola should look like illustration #6. Stain the pergola to the same stain as your deck.

When building a project like the pergola, always use safety gear. Don't attempt to handle the rafters and beams by yourself. This project is a more advanced one than the average do it yourselfer can usually handle. If you do not feel comfortable tackling this by yourself, seek the help of an experienced builder.

The pergola can be embellished with a more decorative approach if you are experienced in wood working. Routing the rafters and cross beams in a pleasing design does much to add to the attractiveness and value of the pergola. If you are not comfortable cutting holes in the deck, consider using post anchors that attach to the deck itself and support the 4 X 4 uprights. Although not as sturdy as cutting a hole and attaching the uprights to the floor joist, it will work well in a protected area.

Give a deck pergola a try. You should be able to accomplish the build on a long weekend, and the results gives new ambiance to your outside deck.

Alden Smith is an award winning author and regular contributor to He writes on a variety of subjects, and excels in research.