How to Build a Corrugated Metal Porch Roof

Build a basic porch frame, one end attached to the house with a 2-by-6-inch ledger or nailer board and the other secured to posts or columns on the porch floor. Remove siding from the house and fasten the ledger with lag bolts driven into house framing. Make sure the ledger is level and nail flashing with a hammer up the side of the house and over the top of the ledger. Add side bands and an end board of 2-by-6 or 2-by-4 lumber, depending on the size of the porch.

Fasten rafters between the ledger and the outside roof frame with metal rafter hangers. Nail these to the ledger and outer band with 8d galvanized nails and a hammer, set the rafters in them and nail them in place through holes in the sides of the brackets. Cover the roof frame with oriented strand board panels, laid perpendicular to the rafters, and seal that decking with roofing paper, stapled to the OSB with a construction stapler.

Begin installing corrugated panels at one corner of the roof bottom, according to the coverage width of the panels and width of the roof; typical corrugated panels are 26 inches wide, designed to cover 24 inches of roof with an overlap between panels. Place the first panel straight with the side and bottom of the roof decking, slightly overhanging both edges, and secure it with aluminum or galvanized screws with plastic washers under the heads. Fasten screws with a screw gun.

Put the first screws on the side at least one corrugation valley inside the panel. Drive screws in the valleys between corrugation ridges, spaced about 18 inches apart, both across and up the roof. Leave the last valley on the inside of the first panel open. Install the second panel with the recommended overlap, usually one ridge and one valley, and fasten it with screws through both panels.

Add panels the width of the roof until it is covered. Buy panels to fit the length of the roof to avoid having to overlap a second row; panels come in lengths of 6 to 20 feet, usually in 2-foot increments. Trim panel tops with tin snips if necessary to fit the length of the roof.

Install top caps where the panels meet the house wall and edge caps or fillers along the sides and at the bottom. Get caps made to conform to the type of corrugation. Follow the manufacturer's directions on installing these. Add a bead of roofing cement on the bottom as extra sealing against water penetration. Reinstall siding at the top of the roof.