How to Repair Flat Roofs

STOPPING FLAT ROOF LEAKS AT SKYLIGHTS AND PARAPETS:
The flashing around the curb of a skylight on a flat roof seldom has to be replaced, but the flashing can pull away from the curb due to the expansion and contraction of the wood that forms the curb. This causes leaks. If the gaskets sealing the skylight are okay, look for the leaking problem at the flashing.

You will have to remove the skylight (probably) from the curb to get to the flashing. Once the skylight is off, the job is easy. Clean away all debris with a broom.

With roofing nails, reset the flashing against the curb, driving the nails flush with the flashing and asphalt building paper and roll roofing that is lapped up against the flashing. Just drive the nails flush to the surface of this material. Then trowel asphalt roofing cement over the area in a fairly thick coating.

If the roofing is damaged where it "folds" or laps up against the curb, you may be able to replace it with a patch. Clean away the stone/gravel next to the curb and lay a piece of asphalt roll roofing in a fairly thick bed of asphalt roofing compound. Fold the roofing gently and lap it up the curb. Then nail it in place. Cover the patch and nails with the compound. Then add stone/gravel and embed it slightly into the compound with the flat of a trowel or shovel.

The wooden curb could be rotted, causing leaking. If this is the case, the curb has to be replaced along with the flashing and the roofing that overlaps both. This is really a job for a professional since the curb may be tied in structurally with the roof framing.

PARAPET FLASHING:
If the roof has a parapet, chances are the parapet is flashed along its top with metal (although sometimes the flashing is just roofing lapped up and over the top).

If flashed and the flashing is damaged you can replace the damaged section easily.

1. Remove any stone/gravel from the area.
2. With a prybar padded with a piece of scrap wood which also acts as a fulcrum, loosen the nails that hold the flashing into position. Then pull the nails. You should be able to lift off the flashing cap now.
3. Clean the area under the cap.
4. Cut a piece of asphalt roll roofing for a patch to fit under the flashing. The patch should overlap the spot that you are repairing at least 4 inches. Embed the patch in roofing compound troweled on fairly thickly. Press the patch in place.
5. Cut another patch that overlaps the first patch by about 6 inches. Coat the first patch with compound and press the second patch in place. Add extra compound at the joints. Use plenty of compound.
6. Replace the flashing over the patch. You'll probably have to bend the flashing for a tight f roofing nails and then seal the nail heads with roofing compound. Replace the stone/gravel to complete the project.

VENT STACK FLASHING:
If the flashing is leaking around a vent stack, you may be able to replace this flashing with new flashing you can buy at many building material outlets and home center stores. The cost is not prohibitive.

1. Remove the stone/gravel around the stack. With a utility knife, cut the roofing membrane at the old flashing. You'll be able to see the outline of it through the roofing. Then with a prybar and scrap wood fulcrum, remove the old base plate of the flashing.
2. With a piece of roll roofing (or buy pre formed), make a patch to cover the area of the old base plate. Cut a round hole in the patch ing material to fit down over the stack. Make this hole a tight ft so the roll roofing laps up the stack slightly. Cover the patching area with compound and embed the roll roofing into it.
3. Now slip the new flashing over the stack, embedding the base of the flashing in a thick layer of compound. Nail the flashing to the roof decking and with pliers crimp the top of the assembly into the opening of the stack. Coat the base of the flashing with plenty of roofing compound and replace the stone/gravel around the repair.