How to Add a Gable Porch Covering

Install posts to support the roof frame. Use 4-by-4 or 6-by-6-inch posts, depending on the size of the porch, usually 8 feet high. Set them in metal column brackets on the porch surface; attach brackets with screws on a wooden floor or concrete anchors on a concrete surface. Space the posts not more than 5 feet apart.

Fasten posts into the brackets with galvanized screws driven with a screw gun. Use a level to make sure they are plumb and the tops are level. Install a 2-by-6-inch ledger board on the house wall at the top of the post level line. Remove house siding and locate joists, studs or other house framing members to hold the ledger.

Mark the ledger location on both sides of the porch and snap a level chalk line to mark the bottom, which should be the same height as the posts. Nail a 2-by-6-inch ledger board along that line temporarily with 16d framing nails and a hammer. Mark spots for the house framing and drill 3/8-inch pilot holes with a power drill through the ledger into the framing. Fasten the ledger with 1/2-inch lag bolts driven with a ratchet wrench into the framing

Install a similar board across the outside posts at the same height. Connect the two ledgers with 2-by-6 framing boards, nailed to the outsides of the posts with two framing nails per post. Make sure these boards are level. Nail them with 16d framing nails.

Order prefabricated trusses to any desired pitch. Get trusses with a slot on top for a ridge board and with a horizontal bottom chord that will rest on the roof frame. Give the supplier the dimensions and the trusses will be made to fit. Order trusses to install at 24-inch intervals inside the roof, but with three extra trusses for the ends.

Set the first truss in place against the house wall, the bottom chord on top of the ledger board. Fasten it to studs in the wall with lag bolts. Nail the bottom chord to the roof frame. Install other trusses at 24-inch intervals to the end of the porch roof. Put double trusses at the end with 2-by-4-inch spacer blocks between them so the last truss chord is flush with the outside of the end ledger board and the next truss is just inside, the width of the 2-by-4 spacer.

Place a 2-by-6-inch ridge board in the slots on top of the trusses. Nail trusses to it from either side. Use a level to make sure it is level.

Nail 1-by-6-inch eave fascia or facing boards at the outside ends of the truss overhangs with 8d galvanized nails. Put metal "hurricane" clips on the ends of each truss where it meets the wall. Fasten with two galvanized nails on each side of the clip, on the truss side and the frame side.

Cover the trusses with oriented strand board panels, perpendicular to the truss chords and with the rough face up. Cut panels to fit with a circular saw and overlap the edges of the panels at the peak. Nail it to trusses with galvanized nails. Install metal flashing to the house wall and over the end of the oriented strand board where it joins. Put metal drip edge flashing on the eaves and rake or sloped ends.

Lay down roofing paper over the drip edge on the eaves and under it on the rake slopes. Staple it to the oriented strand board with a construction stapler. Use a utility knife or shears to cut tabs off shingles for the bottom of the roof. Nail these in place with shingle nails, the cut side up and the other side extending just past the oriented strand board. Cut the width of one tab off a shingle to start the second row, so the joints don't line up. Install shingles to the peak on both sides.

Finish the peak with special cap shingles or use the cut tabs to bend over the peak. Fasten cap shingles with one shingle nail on each side and put the next cap so it covers the nail heads. Seal the nail heads on the last shingle with roofing cement.