Damaged or incorrectly installed roof flashing is the most common cause of leaks. If the flashing is not repaired or replaced, the resulting leaks can shorten the life of the roofing material, damage attics and even destroy ceilings and walls.
Problem: Find the flashing problems
Solution: The most common problem areas are the valley flashing between roof sections, the flashing around a vent and the flashing around a chimney or dormer. Inspect valley flashings for looseness, corrosion or peeling roofing cement. Check chimney flashing to be sure it is captured by the mortar between brick courses. Examine plumbing or attic vents from inside the attic; if daylight shows through, the flashing needs repair.
Problem: Loose nails, holes and corrosion
Solution: If you see loose nails, holes or corrosion, renail or replace the loose nails and cover them with roofing cement. Dab cement on pinholes, but patch anything larger with more flashing material.
To repair flashing material, roughen and clean the area with wire wool, a wire brush or sandpaper. Cut a patch larger than the hole but only as large as there is flat surface to accommodate it. Adhere it with a liberal amount of roofing cement and then cement around the edges of the patch.
To replace seriously corroded flashing, remove the old flashing plus several rows of shingles around it. Remove the shingles carefully so you can re-use as many as possible. Apply roofing cement under the flashing and 6 inches under the flashing edge.
To repair roof edge flashing, lift and re-adhere the shingles at least 6 inches back from the edge. Don’t seal the drip edge along the eaves, as this is a water passage.
Problem: Flashing is leaking at the chimney
Solution: Remove shingles to expose the flashing. Try to preserve them for reuse. Chip out the counter flashing and save it as a template for making the new flashing piece. To repair the step flashing beneath, slide new flashing pieces under the damaged areas and caulk along the edges of the flashing, using masonry caulk. If the step flashing is beyond repair, install new flashing, working from the bottom up. Step flashing should extend at least 4 inches out onto the roof and 2 to 4 inches behind siding, trim or counter flashing.
Install new counter flashing; seal the seam between the mortar and step flashings with urethane roofing cement or silicone caulking compound. The step into the chimney brickwork should be 1½ inches. Reinstall the shingles, securing them to the flashing with roofing cement.
Problem: Vent flashing is corroded or damaged
Solution: To repair vent flashing, purchase a vent-flashing flange that covers the old seal or remove the old flashing and install a new one. If you install new flashing over existing flashing, you will have fewer shingles to remove, but you will have to cut the roofing nails to slide the flashing under the existing shingles.
Be careful not to damage the roofing paper or break the shingles. Nail the flashing in place and apply roofing cement around the nails and any holes you’ve made. Caulk around the top of the flange and install any shingles you’ve removed. Make sure the shingles lie flat above the flange.
To replace the flashing around the vent pipe, remove the shingles covering the existing flange at the back and sides. Use a hacksaw blade to cut the nails. Pry and lift off the flashing, and pull or cut off any nails. Position new pipe flashing over the vent, push it into place and nail it where shingles will cover. Replace the shingles, and cover the nails with roofing cement.
Captions:
1. To replace the flashing around a vent pipe, remove the shingles covering the existing flange at the back and sides.
2. Pry and lift off the flashing, and pull or cut off any nails.
3. Position new pipe flashing and push it into place under the shingles.
4. Nail the flashing in place.
5. Apply roofing cement around the nails and on any holes you’ve made.
Tip: Flashing is galvanized steel, aluminum, copper, roll roofing, plastic and even rubber. Never mix metals when nailing flashing: The electrolysis generated causes rapid corrosion.