How to Build an Awning on an Existing Deck

Determine the height you want the awning to stand at above the deck. Add to this the height of the deck from the ground. Add an additional foot to find the length of your front support posts. Cut two lengths of 2-by-4 to this length, using a circular saw.

Add 6 inches to the length of your front support posts to find the length of the rear support posts. Cut two pieces of 2-by-4 to this length. Varnish the front and rear support posts, using exterior grade varnish and a paintbrush. Measure the length and width of the deck, using a tape measure. Cut two pieces of 2-by-4 to the length of the deck and 2 pieces of 2-by-4 to the width of the deck.

Cut a 1-by-1-by-4-inch notch out of the ends of the deck length and deck width pieces, using a hacksaw. Interlock the cut ends of these pieces to form a 4-inch thick rectangular frame the length and width of the deck. Fasten the interlocked joints together with two countersunk long screws per joint, using a hammer drill and screwdriver drill bit. Screw plywood sheets to the top of the frame to form the awning.

Varnish the awning. While the varnish is drying, dig a 1-foot deep hole at each corner of the deck, using a shovel. Prepare a batch of concrete from 1 part cement, 3 parts sand and 1 part water. Plant the front support posts in the front two holes and the rear support posts in the rear two holes. Fill around the posts with concrete. Allow 48 hours for the cement to set.

Set two step ladders on the deck, one by a front support post and the other by the opposite rear support post. Raise the awning to the top of the support posts with the help of an assistant. Fix the awning to the support posts, using L-brackets. The awning will slope forward in order to keep rain from pooling on it.