How do you fix a roof leaking around a vent pipe?
Short answer. The lasting fix is to replace the pipe boot: lift the shingles above the pipe, remove the old flashing, slide a new boot over the pipe with its flange under the upper shingles and over the lower ones, nail it, and reseal the shingles. Slip-over collars and sealant can buy time, but they are stopgaps.
Repair options, from best to quickest
- Full boot replacement: new flashing woven into the shingles, with a rubber, silicone or lead boot sized to the pipe. On cast iron pipes, lead or silicone tends to outlast standard rubber.
- Retrofit collar: a rubber or silicone sleeve that slips over the existing boot and seals to the pipe. Useful when the base flashing is sound and only the collar has cracked.
- Lead boot with a top fold: soft lead flashing whose top is folded down into the pipe. Long lived, though squirrels sometimes chew it.
- Sealant only: a bead of roofing sealant over a crack. Temporary until a proper repair.
What a proper replacement includes
- Break the seal on the shingles above the boot without tearing them.
- Pull the nails holding the old flange and slide it off.
- Check the deck around the hole for soft or dark wood, and replace it if needed.
- Install the new boot so the upper half of the flange is under shingles and the lower half sits on top.
- Nail where specified, reseal the lifted shingles and confirm the collar is snug around the pipe.
During a full replacement
Every pipe should get a new boot regardless of age. Reusing old boots on a new roof is a shortcut that leads to leaks within a few years. See pipe boot leaks and roof flashing explained. If the leak damaged ceilings, read about interior water damage coverage.