Building a Pergola on a Deck

The simplistic design and square shape of a pergola makes it a great DIY project. 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.

Step 1 - Create 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 4x4 cedar posts for construction. The pergola will be an 8 foot 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.

Step 2 - Lay it Out

Begin by laying out your 8x8 foot area. This will be measured from the 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 inches on center.

Step 3 - Make the Measurements

Determine the inside edge of the joist as a starting point, and mark it. Measure 8 feet along this joist, making another mark. Snap a chalk line between these two points. Drive a 6D nail halfway in at the mark, and use it as a measuring point for other legs of 8-foot square.

Step 4 - Make the Cuts

From your starting point, use a short length of 4x4 to lay the outpost hole on deck. Cut a 4x4 hole in the decking. With the aid of a helper, stand the post on one end, and carefully place it in the 4x4 hole. Drill two ½ inch offsets holes through the post and joist. Secure the post with the 6 inch carriage bolts. The offset helps maintain structural integrity. Repeat for the remaining three posts. Measure each post 8½ feet from the deck, and cut each at this mark.

Step 5 - Attach the Cross Beams

Align two 2x8x10 inch boards, and screw them together, working from both sides to ensure that they don't buckle. Repeat for the other side.

Attach it to 4x4 cedar posts, using 7x1/2 inch carriage bolts. Allow an overhang of each cross beam to be equal on each end. These cross beams may be given a more detailed design by routing the ends.

Step 6 - Attach the Rafters

The five 2"x6"x10' cedar boards will be placed equidistant on the pergola. Find the center of the board. Mark each end, allowing for an overhang. Mark both sides of the board from the center. Fasten rafters to cross beams with 2½ inch galvanized screws. Stain the pergola to the same stain as your deck.

Safety First

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 DIYer can 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 woodworking. Routing the rafters and cross beams in a pleasing design adds 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 4x4 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.