What is pipe jack roof flashing, and which type should you use?
How a pipe jack sheds water
The base is shingled in like a shingle itself. Its upper half slides under the course above, so water running down the roof passes over it, and its lower half sits on top of the course below, so water exits onto shingles rather than under them. Nails go along the top and sides where the next course covers them. A jack lapped backwards, or one with exposed nails along its lower edge, leaks no matter how good the collar is.
The main types
- Rubber collar on a metal base: the standard on most Georgia homes. The collar is the weak point; years of sun crack it and water runs down the pipe into the attic, often long before the shingles wear out.
- Silicone collar: handles heat and UV better than older rubber and is a common upgrade during a replacement.
- Lead jack: a soft lead sleeve folded down into the top of the pipe. Long lived, but squirrels chew it and the fold can split.
- All-plastic base: will not corrode but can crack under foot traffic or impact.
- Split retrofit boots: wrap around the pipe over the old jack. Useful as a stopgap, not a substitute for proper shingle lapping.
Size and fit
House vent pipes are usually 1.5, 2 or 3 inches, sometimes 4. Buy the jack for the actual pipe size, since a stretched or oversized collar will not seal. Most jacks cover a range of pitches, but a steep roof may need a jack made for that slope.
Repair or replace?
A cracked collar on an otherwise healthy roof is a small repair. During a full replacement every jack should be new, because reusing old ones saves little and they are a leading leak source. See pipe boot leaks and common causes of roof leaks.