How do you repair a roof vent pipe boot?
Short answer. A cracked vent pipe boot is repaired either by sliding a replacement rubber collar over the old boot or, better, by replacing the whole boot, which means unsealing the shingles above it, pulling its nails, and sliding a new flashing in. Caulking the crack only buys time, because the sun keeps breaking down the rubber.
Three ways to fix it
- Slip-over repair collar: a rubber sleeve that slides down the pipe and seals over the cracked collar. Quick and cheap, and reasonable when the base of the old boot is sound and lying flat.
- Full boot replacement: the shingle courses above the boot are carefully unsealed, the nails holding the old flashing are pulled, and a new boot goes in with its upper flange under the shingles and its lower flange on top of them. Exposed nail heads get sealed and the lifted shingles are resealed. This is the standard repair.
- Lead or long-life boot: a lead flashing dressed down into the pipe, or a boot with a more durable collar, outlasts standard rubber in the Georgia sun. Squirrels sometimes chew lead, so some homes also need a cap or guard.
Measure first
Boots are sold by pipe size, with 1 1/2, 2, 3 and 4 inch the usual choices. A collar that fits loosely leaks, and one stretched over too large a pipe splits early. Check the roof pitch too: the base has to sit flat on the deck without buckling.
Look for collateral damage
A boot that leaked for months may have soaked the decking around the pipe. From the attic, look for dark staining or soft wood around the pipe opening, and look at the insulation below for stains. Rotted decking should be cut out and replaced before the new boot goes on, or the new boot will be nailed into wood that cannot hold it.
More detail on why boots fail and how fast is in pipe boot leaks, and other leak sources are covered in common roof leak causes.