How to Build a Pergola on a Cement Foundation

Identify the location of your pergola and measure the cement slab. This slab must be at least 3½ inches thick to support the weight of a pergola. Mark the locations where you want your posts using a pencil or tape. Measure across the square or rectangle, between opposite corners, to determine if your pergola is square.

Position your first post anchor and mark where the hole must be drilled into the cement. Drill the holes using a hammer drill and mason bit. Secure the post anchor with ¼-inch masonry screws, and repeat on the other three corners of the pergola.

Determine how tall your pergola will be and cut your four posts with a miter saw. Reseal your posts and let them dry.

Lay out your pergola design near the installation area to determine the length of your stringers, or roof beams, and beams. Add up to 1 foot of length on each side of the beams and stringers. Draw the design you want at the end of your first board and cut it out with a jig saw. Position a bucket on the edge of the board for a simple arc design or draw your own design with more detail. Use the first cut board as a template and outline it on the ends of the rest of the boards. The design should be entirely outside the post area of your pergola, so add enough room on the ends of the board so the entire width of the board, all 6 inches, will attach to the post or beams. Cut the remaining boards, seal them and let them dry.

Install your posts. Set your dry posts into the post anchors you installed in Step 2. Have someone hold the post up while you hammer the nails into the anchors and posts. Level each post before you tighten down the brackets completely.

Install the beams on the front and back of your pergola. The beam will sit 4 inches below the top of the post. Have a friend hold your post level while you are installing the beam. Hold the beams in place using clamps if you do not have enough help. Position and secure the beams with 3-inch screws. Install one beam on the front of the two front posts and one on the back. Repeat on the back two posts, securing them together. Check to make sure your posts are still level before installing your stringers.

Notch your first stringer so that it will fit over your beams. Make 2-inch deep notches. Cut the notches with either a dado blade on a table saw or a jig saw.

Install the stringers using 5-inch screws screwed down from the top of the stringer and into the beams. Screw the edge stringers into the posts that are still sticking up above the beams to create additional stability. Set your stringers as far apart as you want, but make sure they are all the same distance from each other.

Repeat Step 8 on your 2-by-4 slats that will go across your stringers, and install them with 3-inch screws. The post will not be sticking above the stringers, so there is no need to secure the slats into the posts.

Cut your 1-by-5 lumber to the length of your post, leave a notch where the stringers dip down on your post area. Cut the notch out with a jig saw. Use the first notched trim piece as a template, but make sure it fits in all four posts. Install the lumber on the outsides of the posts. Seal the trim and install it with finishing nails.

Create and install your braces. Measure and cut the length of your first brace. Cut both ends at 45-degree angles. This should fit securely against the post and through the beam. Draw out an arch on one side and cut it out with a jig saw. Use this as a template for the four braces that attach the beams to the posts. Repeat the process for the stringer braces, which will be slightly longer than the beam braces. Install the braces to the post by drilling into the brace and post and using 5-inch screws. Screw the braces into the beam and stringer using 3-inch screws. Screw them in between the two beams or two stringers and to the inside beam or stringer.

Make and install your post caps. Cut four squares out of your 2-by-6-inch board. They will be about 5½ inches square. Set your saw blade on your table saw to 15 degrees and cut all four sides of each square. Clamp each square to a longer piece of wood while you are sawing to protect your fingers and give you more control. Seal the wood and let it dry. Nail the post caps on the top of each post using galvanized finishing nails.