Vent pipes and appliance chimneys are sealed with metal flashing to prevent roof leaks, but roof flashing may eventually need a replacement.
Pitched roof vents are usually flashed with a flat metal sheet cut to fit around the pipe, and a protective collar that fits around its base. Flat roof flashing usually covers the entire vent, with a flat base and a pipe casing that slides on over the chimney. Replacing either type of flashing is fairly easy. Make sure your replacement roof flashing is exactly the same type and diameter as the old one. Follow the roof safety procedures when working on this roofing project; as a helpful reminder they are outlined here.
Caution: Wear work gloves when working with metal flashing because the edges of the flashing are sharp.
On a pitched roof, the base of the flashing is covered with shingles on the side above the chimney, and left exposed on the side below it. To reflash a vent pipe on a pitched roof follow the steps outlined below:
- Remove roof shingles on the up-roof side of the chimney. Lift the shingles with a pry bar, but be careful not to damage them, as you will have to replace them to cover the new roof flashing. If you break a shingle, you will need a new one to replace it, so be careful.
- Remove the flashing by inserting the blade of the pry bar under its edge, and lever the bar on a block of scrap wood to lift the flashing.
- Lift the roof flashing up over the vent pipe, being careful not to knock the pipe out of place. Then pull out any nails left around the pipe, and fill the holes with roof cement.
- Set the new flashing over the pipe, with its protective collar aligned the same way the old one was. Nail down the roof flashing with 6d galvanized roofing nails, and cover the nail heads with roof cement. Apply more roof cement to seal the base of the protective collar.
- Replace the roof shingles over the top of the flashing. Starting with the bottom row and working up, nail each roof shingle into place at the top. Use two 6d galvanized roofing nails for small roof shingles, four nails for large ones. As you work, cover the nail heads with roof cement. It is important to avoid water leaks later. Slide the top edges of the top row of shingles under the overlapping bottom edges of the row above.
If you have a problem when reflashing roof vent pipe or doing another type of roof repair, we recommend to consult with an experienced roofing contractor from a local roofing company. Shop around and you may find a roofing specialist that is willing to share some helpful information without charge.