What Is the Purpose of Lead Boot Flashing for a Roof?

Definition

• Also called a vent boot, boot flashing is a piece of square or rectangular flashing that has a rubber sleeve in the middle. The flexible sleeve forms a tight seal around the round plumbing vent. At one time, boot flashings were made from lead, which is durable and flexible, so they are still sometimes called lead boots. These days, they are usually made of copper, aluminum or plastic.

Use

• Using a lead boot is simple. The rubber sleeve slides over the roof vent, and the rectangular base slides up under one or two courses of overlying shingles. The flashing is nailed under the overlying shingle, which keeps the nail holes dry and leak-free. Roofing cement is usually used to keep the bottom half of the flashing tight against the roof.

Problems

• The rubber collar, which is exposed to sunlight and temperature extremes, inevitably becomes stiff and loses its tight seal. You need to replace it when this happens. If parts of the flashing are face nailed on top of the shingles, the roofing cement used to seal the nails can get stiff and fail, requiring a touch-up.

Tips

• Ideally, you should only have to replace boot flashing when you replace the shingles. Always use the highest quality boot flashing available so it lasts as long as your roof. On slate roofing, the flashing is nailed between the slots of the upper course and sealed with metal bib flashing.