DIY Flat Roof Installation

Prepare the roof by building in a slope; no flat roof can be really flat or it would not drain. The best option is to have roof joists set at a slight angle, at least 1/8-inch per foot, which should be done when the roof is framed over the walls. Achieve the slope, if the roof joists don't provide it, by ripping 2-by-4-inch boards into thin wedges with the proper slope and nailing them to the top of the joists.

Deck the roof with 5/8-inch plywood nailed with a hammer and roofing nails on the joists; leave a 1/8-inch gap between sheets at the joints to allow for expansion and contraction. Cover the decking with a 1/2-inch thick rigid foam material called iso board; it is made of a foam, polyisocyanurate. Screw this with a screw gun to the decking with galvanized steel screws with galvanized washers. Place sheets tightly together. Trim edges to fit with a utility knife.

Clean the roof to remove any debris or eliminate any objects that might puncture the rubber material. Cut EPDM sheets to fit with big shears or a utility knife; the material comes in 10-foot wide rolls. Add an extra 9 inches all around for overhang. Overlap seams by 6 inches if more than one strip is required to cover the roof.

Lay the EPDM in place to test fit it. Make any necessary adjustments, like cutting holes to fit over any exhaust vents. Smooth the EPDM on the foamboard. Fold half of it back over the other half to apply EPDM contact cement. Work down from the high side of the slope.

Use a 1/4-inch nap paint roller with a long handle to spread glue on the exposed iso board and the folded half of the EPDM. Work carefully -- the contact cement will bond immediately if it comes in contact with another cemented surface. Let the glue dry to the touch, then get down on your knees and begin rolling the cemented EPDM over the cemented iso board. Work slowly, pushing the folded section from the inside onto the cemented board. Work in small sections from side to side.

Fold the other half of the EPDM over the cemented material and repeat the gluing process. Leave any overlap at seams unglued, but glue 6 inches down over the edges of the roof. Use a dry paint roller to smooth out any bubbles once the entire roof is covered. Fasten any seams with a rubber adhesive and seal them with a 12-inch wide strip of uncured rubber, glued with the rubber adhesive.

Screw on metal brackets called termination stops to fasten the overlapped edges on the sides of the roof. Install a metal drip edge flashing called gravel stop, which is especially made for flat roofs around the edges of the roof. Secure it with nails and a hammer, and seal the roof side with a 12-inch strip of uncured rubber cemented to the flashing and the EPDM surface with rubber adhesive.