Roof Vent Pipe Boot Leaks: How to Spot and Replace One

A cracked rubber collar around a plumbing vent pipe is one of the most common reasons a roof leaks, and one of the cheapest to fix. The boot is a rubber collar on a flat base that seals the gap between the pipe and the shingles. Sun and temperature swings split the rubber long before the shingles wear out, and a homeowner can replace one in an hour or two on a low, safe roof.

How to tell the boot is the problem

Suspect the boot when the stain or drip is on or near a ceiling below a vent pipe, often in a bathroom or kitchen. Confirm it before you buy anything:

  • In the attic, follow the vent pipe up and look for water stains or wet insulation around it, or daylight where the pipe meets the roof.
  • On the roof, look at the rubber collar. A split, a crack running around it, or a visible gap between the collar and the pipe means the seal has failed.
  • Check the flange too. If the metal or plastic base is cracked, or nails have backed out, the whole boot has to go.

If everything looks sound, the leak is probably elsewhere, and how to find a roof leak shows how to trace it.

What you need

  • A replacement boot made for your pipe. Measure the pipe’s outside diameter, since plumbing vent pipes are commonly between 1.5 and 4 inches.
  • A flat pry bar, a utility knife, a hammer and a caulk gun.
  • Roofing nails, roofing cement and polyurethane or roofing sealant.
  • Gloves, eye protection, and a ladder that reaches at least 3 feet above the eave.

Pick a mild, dry day. Shingles crack when they are cold, and a cracked shingle next to the new boot defeats the repair.

How to replace the boot

  1. Loosen the shingles on the sides and above the boot with the pry bar, working slowly so the nails and shingles are not broken. This exposes the old flange.
  2. Cut off the old collar with the utility knife and remove the old boot, pulling or cutting any nails holding the flange.
  3. Clean the surface so the new boot lies flat, and check the pipe for cracks.
  4. Slide the new boot over the pipe. Its base must lie flat on the roof and cover the old opening, with the upper part of the flange under the shingles above and the lower part over the shingles below.
  5. Nail the flange along its upper edge and sides, then lay the loosened shingles back over the nail heads so no nail is left exposed.
  6. Seal it. Put roofing cement under the shingle tabs that overlap the flange, and run a bead of polyurethane sealant where the collar meets the pipe.
  7. Check it in the next rain, from the attic if you can.

If the flange and the pipe are sound and only the rubber has split, a slip-on repair collar that fits over the old boot is a quicker, lower-effort fix. It replaces the seal but not the flashing beneath it, so it is not a cure for a failed base.

Mistakes that bring the leak back

  • Sealing over a cracked collar with caulk instead of replacing it.
  • Laying the flange the wrong way, with the upper edge on top of the shingles, which lets water run underneath.
  • Leaving nail heads exposed on the flange.
  • Buying a boot that does not match the pipe size.
  • Replacing one boot and ignoring the others on the roof, which have aged at the same rate.

When to hire a roofer

Call a roofer if the roof is steep or high, if the shingles around the pipe are brittle and break when lifted, or if the leak continues after a new boot. A professional replacement typically costs $150 to $400 (see how much it costs to repair a roof). For other leak locations, how to fix a roof leak sets out which repairs are DIY and which are not, and shingling a shed roof shows how shingles are laid over flashing.

More roof leak guides

The Roof Leak Finder points to the likeliest cause from where and when the water appears.

Conclusion

A vent pipe boot leak is easy to confirm and cheap to fix: look for the split collar, buy a boot that fits the pipe, and replace it with the flange tucked under the shingles above and over those below. If your roof has had one boot fail, inspect every other boot, since they have all had the same sun.

Luca Clements

60 articles

Related articles