How to Build a Gable Over a Door

Design the gable, specifying the width, height, depth and roof pitch, as well as the support posts, columns or brackets. Use prefabricated trusses for a large gable, and cut rafters for a small one. Remove any siding above the door, and identify rim joists, wall plates or studs solid enough to support a gable end. Leave wall sheathing intact.

Locate positions for any posts or columns. Mark them on the entryway with chalk. Use a level and chalk line to snap a level line above the door at the bottom of the planned gable. Using 2-by-6-inch framing lumber, cut a pair of rafters to the desired pitch, along with a horizontal ledger board that will go at the bottom. Fasten the rafters and ledger, which serve as the truss, to the wall framing. Use lag bolts, driven with a ratchet wrench.

Install your posts or columns at the selected locations. Use metal post brackets, fastened to the entry floor with screws or concrete anchors.. Fasten brackets to wall framing with lag bolts if you're using those to support a short roof. Use a level to make sure your work is level and plumb.

Fasten 2-by-6-inch band beams between the doorway ledger and the outer supports -- either the posts or the ends of the brackets. Fasten these with a hammer and 16d framing nails driven through the beams into the ledger or posts. Cut another 2-by-6 board to go across the outside edge of the roof frame. Nail it to the ends of the side beams.

Set another set of rafters or truss at the outer edge of the frame. Nail the rafter or truss ends to the side beams with framing nails Use metal hurricane ties, plates that overlap the wood joints, for extra support; fasten these with 8d galvanized nails driven into the beams and the rafters. Add internal rafters or trusses with centers 24 inches apart between the wall and outer beam.

Put a 2-by-6-inch ridge board horizontally at the peak, between the rafter tops, for a deep roof; leave a 1 1/2-inch gap at the rafter tops when cutting to make space for this. A ridge board is not necessary with prefabricated trusses, which have internal bracing. Nail rafter tops to the ridge board; use a level to make sure it is straight.

Cover the gable entry with oriented strand board or plywood decking nailed to the rafters or truss tops with 8d nails. Extend it an inch or so beyond the edges of the roof to allow for trim boards. Overlap panels at the peak; extend one panel to the top of the peak, and cover the edge with a panel from the other side.

Secure roofing paper with a construction stapler on the gable sides; overlap paper at the peak. Nail metal flashing with shingle nails on all edges of the roof and against the wall. Put flashing under the paper on the sides and over it on the gable angles. Put it under the paper at the wall, one side up the wall and the other down the roof.

Add 1-by-6-inch fascia or facing boards along the roof eaves. Install shingles on both sides of the roof, and cover the peak with cap shingles, overlapping that point on both sides. Replace siding on the house; set siding boards firmly against the shingles at the joint. Install siding across the gable end, trimming boards to conform to the roof angles.