How to Support a Shed Roof Over a Patio

Identify a place on a house wall to attach one end of the shed roof; it must be high enough to allow a slope of at least 2 inches per foot to the outer edge, for instance 20 inches higher than the outside posts for a 10-foot wide patio. Locate house framing to support the roof, rim joists on a two-story house, bottom wall plates or studs on a one-story house.

Remove the house siding with a pry bar at the chosen height and the width of the patio. Mark the locations of the studs or other attachment points. Measure the proper height with a tape measure on both ends of that area and snap a level chalk line to mark the top of a 2-by-6-inch ledger board, to extend 1 1/2 inches past the patio width on each end.

Fasten the ledger temporarily with a hammer and 16d framing nails on each end. Drill pilot holes with a power drill and a 3/8-inch bit through the ledger board into the studs behind the wall sheathing. Install 1/2-inch lag bolts in the holes to secure the ledger, one bolt into each stud or every 16 inches if fastening to wall plates or rim joists. Drive lag bolts in with a ratchet wrench.

Install posts at the other end of the patio. Secure them to the patio deck with metal brackets which sit on the patio surface and are fastened with concrete screws into a masonry surface or dig holes outside the edge of the patio to set posts. Dig post holes to a depth one-third of the post, about 2-1/2 feet for a post with a final height of 8 feet. Set poles plumb with a level and secure them with concrete mixed in a wheelbarrow and poured into the hole.

Attach beams to the ledger and the posts. Use 2-by-6-inch boards for most patios, nailed with 16d framing nails to the end of the ledger and the outside of the posts; secure the ledger end if desired with joist brackets, nailed into the face of the ledger with u-shaped slots to support the beam. Put another 2-by-6 across the outside of the posts. Add rafters at 24-inch spaces between the beams to connect the ledger and the outer frame.