Why is my roof leaking by the vent pipe?
Short answer. Most leaks at a vent pipe come from the pipe boot: the rubber collar cracks and pulls away from the pipe, or the flashing was installed with shingles under it instead of over it. Less often the water is condensation in or on the pipe, a cracked fitting in the attic, or a leak higher on the roof that runs down to the pipe.
Narrow down the source
- Look at the boot with binoculars. A gray, cracked or split rubber collar, or a gap between collar and pipe, is the usual answer.
- Check the attic during or after rain. If water runs down the outside of the pipe from the deck, it is the boot or flashing. If the pipe is wet only on a cold morning with no rain, it is condensation.
- Follow the stain uphill. Water can enter at a nail, a damaged shingle or a skylight above and travel along the deck to the pipe.
- Look for chewed lead. Squirrels gnaw lead boots at the top fold, opening a hole.
- Check the pipe joints. A cracked coupling in the attic tends to leak sewer gas and condensation, not rainwater.
Why boots fail early
The rubber collar faces full Georgia sun, heat cycles and ozone, so it often wears out years before the shingles, sometimes in under ten years. Boots that were never sized to the pipe, or plain rubber seals on cast iron pipe, fail sooner.
Do not wait
Even a small drip soaks insulation and the deck around the pipe, softening the plywood and staining the ceiling. A bead of roofing sealant around the collar buys time but is not a repair. Robust Roofing's guide to leaks when the shingles look fine covers other hidden sources. Read pipe boot leaks for repair options and common causes of roof leaks for other suspects.