Archive for Monday, September 10, 2012


Fix-It Chick: Install a vent pipe flashing

September 10, 2012


Most homes have several vent pipes protruding from various spots along the roofline. Some of these are bathroom or sewer vents, while others are for hot water heaters, furnaces or other home appliances.

Regardless of their purpose, over time the seal between the pipe and the roof begins to fail and this creates a potential for serious water damage. Installing a pre-made roof flashing can prevent or end this type of damage.

Step 1: Roof flashings are sized according to the inside diameter of the vent pipe. Measure the pipe opening to determine the correct size.

Also note the pitch of the roof where the flashing is to be installed. The pitch of any roof is the number of inches it drops vertically for every 12 inches it extends horizontally. To determine the pitch of a roof, mark a spot 12 inches from the end of a level. Set the bottom corner of the level on the roof and extend the level out over the roof, allowing the center gauge to read perfectly level. Use a measuring stick to measure the distance from the 12-inch mark on the level to the roof directly below it. The number of inches the roof drops is the numeric roof pitch.

Step 2: Choose a flashing style both for aesthetics and durability. Galvanized or aluminum flashings with rubberized collars are durable and easy to install but may not be aesthetically pleasing on a black shingled roof. Polypropylene flashings are aesthetically pleasing on dark roofs, but may be considered an eyesore on light-colored roofs. Check the pipe size, roof pitch and temperature rating before making any purchase.

Step 3: Remove as much of the old flashing material as necessary to allow for an unobstructed seal on the new roof flashing.

Step 4: Apply several beads of silicone caulk to the underside of the new roof flashing.

Step 5: Slide the flashing collar over the vent pipe with the larger side of the flashing base on the upside of the roof. Visually align the flashing to correspond with the roof pitch.

Step 6: Slide the flashing down toward the roof and tuck the upper edge of the flashing beneath the shingles located on the upper side of the vent pipe.

Step 7: Firmly press the flashing into place, allowing the downside edge to rest on top of the shingles.

— Linda Cottin can be reached at


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