How Do I Install Roofing Flashing?

One of the least understood aspects of the roofing process is the installation of roof flashing. The importance of correctly installing roof flashing cannot be stressed enough. Without properly installing roof flashing water would be able to leak inside the building structure. Roof flashing is found at strategic locations on the roof such as along vertical walls, skylights, chimneys, dormers, vent pipes, and in valleys. It prevents water from penetrating those areas and causing damage to the decking which in turn leads to wood rot and mold.

Roof flashing is made of various material such as copper, steel, lead, and aluminum. It comes in various sizes and shapes and is often custom made by hand for certain areas of the roof by the professional roofer installing the roof project. The flashing in many instances will also need to be sealed with a water proofing roofing cement.

There are many types of roof flashings…  here are the steps to installing some of the most common ones. (1.)  “Chimney Flashing.” With a diamond bit saw cut an indention into the brick and using counter-flashing press it into the indention. The flashing should hang in a manner in which it will overlap the base flashing two to three inches. Use roof sealant to secure the flashings together and to the chimney then use roofing caulk to fill the indention on the chimney.

(2.) “Valley Flashing.” Valley flashing is usually made of aluminum. Take the aluminum flashing, generally 18 inches, and place it in the valley where two roof sections come together.  Evenly space the flashing over the center on both sides to fit the valley. Run the entire distance of the valley with one piece of flashing if possible. Cut the flashing to match the eaves and ridges Seal the outside edges of the flashing with roof sealant and nail the flashing along the outside edges.

(3.) “Drip Edge Flashing.” Drip edge flashing is installed to the edges of the roof before the shingles are installed. It “generally” comes in 10 feet lengths and is 1 ¼, 1 ½, and 2 inches in width and is nailed directly to the roof decking.  Because drip edge has a small lip that kicks water out and away from the fascia, the flashing protect from water damage.

(4.) “Vent Pipe Flashing.” There are two types of vent pipe flashings. One is the lead boot. It is made of lead and has a flange and sleeve. It is installed over the protruding vent pipe. The flange is nailed to the deck and the top of the sleeve is turned down inside the pipe.  The other type of vent pipe flashing has a tight fitting rubber boot that slips over the pipe and the base of the flashing is sealed with roof cement and nailed to the roof decking.

Proper installation of roof flashing is critical to the overall performance of any quality roofing system.


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