How to Make a Pergola Roof on a Deck

Measure your deck and draw up plans for your pergola roof according to the deck size. Make the basic frame of the pergola roof the same size as your deck, so the last board running in one direction is in line with the edge of the deck below it. Let the ends of the roofing pieces that run perpendicular extend just past the edge of the deck.

Measure and mark a square for a 4-by-4 post at the corner of your deck, just inside the corner formed by the two outermost deck joists, provided you have a wooden deck. Cut out the square in the deck and slide the 4-by-4 post into place until its bottom edge is even with the bottom edges of the two joist pieces. Drill holes through the joists and into the post; affix the post with carriage bolts. Repeat the procedure to erect posts at all four corners of the deck.

If you have a concrete or brick deck, dig holes at least 18 inches deep directly outside each of the corners of the deck. Fill the holes with concrete and set the 4-by-4 posts directly into the concrete. Use a measuring tape and a level to ensure that the posts are plumb and evenly spaced.

Cut two 2-by-8 boards so they are equal to the distance between two posts plus 2 feet. Hold each board in place, horizontally, at opposite sides of the pergola; the top of the board should be level with the tops of both posts. The ends of the boards should extend beyond the posts by about 12 inches on each side. Drive two 3-inch wood screws through the board and into the post at each end.

Measure and cut enough 2-by-6 boards to fit along the length of your pergola, perpendicular to the 2-by-8 boards you've already installed. Allow a 1-foot overhang past the 2-by-6 support beam. Space the 2-by-6 boards no more than 2 feet apart.

Use a dado blade to cut 2-inch-wide grooves into the 2-by-6 boards at regular distances, spaced no more than 2 feet apart. Cut each groove so it extends about halfway through the board. Set the second layer of 2-by-6 boards perpendicular to first layer of boards, lining them up with the grooves. Mark the uncut second layer of 2-by-6s at each intersection. Cut 2-inch-wide grooves into these boards as well, extending halfway through them. On the ground, fit the boards together so they interlock at each of the grooves.

Disassemble the pieces of the frame and mount them, one by one, on the pergola structure. Drive the 3-inch wood screws through the boards at each intersection to hold them together.