What is a plumbing-drainage vent pipe?
Most bathrooms have drainage vent pipes running up through the house walls, attics, and roofs to offset the pressure fluctuations caused by flushing the toilets. These pressure-equalizing vents prevent wastewater backup and other problems. A one-bathroom house will have one vent pipe. A multiple-bathroom house will have several, depending on where the bathrooms are located. By looking at the roof of the house itself, these vents normally appear as uncovered 1-to-4-inch-diameter pipes protruding vertically through the roof by six inches or more. The flashing and seals are located at their shingle-level bases.
What is vent-pipe flashing.
Vent-pipe flashing is a rectangular piece of sheeting having a raised oval-shaped crown at its center with a circular rubbery seal and pipe-hole centered atop the crown. This flashing is fitted down over these pipes before the roofing is laid over its base. Most of this flashing is made from thin aluminum or hard-plastic sheeting. The flexible rubbery seal on top of the crown fits tightly around the pipe by squeeze-gripping it. This seal prevents any rain water from leaking downward around these pipes.
The hot sun drys-out the rubbery seal, which, in turn, cracks and falls apart, causing leakage. This damaged condition allows rain water to leak down the outside of the vent pipe, which, in turn, stains and ruins the inside ceilings and walls adjacent to it.
If caught early, applying a stretchable caulk to the seal part itself will repair it for a while. However, once the dry damaged seal begins to fall apart in chunks, the caulk could break loose with it, allowing major leakage. A more effective professional-looking way to repair the seal, is to double-up on it. This repair is done by cutting out the crown-and-seal from a new flashing and slipping it over the current crown-and-seal installed already. A new flashing can be found in most major hardware outlets for about $5. Some of the plastic ones have a tall crown and heavy duty seal, which will aid this overlapping repair. Moreover, this second-layer can be installed long before the original seal begins to dry out or leak, which gives added protection, early.
Normally, to repair a leaking vent-pipe seal, the whole flashing is removed first. This task involves taking up all the shingles around the flashing base, and then replacing them after the new flashing is installed. But, when a second crown-and-seal is fitted atop the old one as explained above, the bottom-end of the new crown will fit onto or near the old flashing base. There, it can caulked for a sturdy leak-proof attachment. No shingles need to be removed, which makes this repair fast, effective, and affordable.