CSLB C-39 Roofing ContractorSteep-Slope RoofingMedium
A roofer is installing a new asphalt shingle roof and needs to properly flash a pipe penetration. The pipe has a diameter of 4 inches. What is the generally accepted minimum width of the flange on a pipe boot or flashing collar, extending over the shingle course below, to ensure adequate waterproofing?
- A2 inches
- B6 inches
- C4 inches
- D3 inches
Show answer & explanationAnswer & explanation
Correct answer: C. 4 inches
For pipe penetrations, the flashing flange (apron) should extend a minimum of 4 inches beyond the pipe's edge in all directions, covering the shingle course below and allowing for proper sealing. This provides sufficient coverage for water shedding.
Why the other options are wrong
- A. 2 inches is generally too narrow for a pipe flashing flange and may not provide sufficient overlap for waterproofing.
- B. 6 inches is more than sufficient but not the *minimum* required, and could be considered excessive for standard pipes.
- D. 3 inches offers some protection but is often considered insufficient for critical penetrations like pipes.
Pipe Flashing Flange Width
The flange of a pipe boot or flashing collar is the flat, horizontal portion that extends out from the pipe base, designed to integrate with the roofing material for watertightness.
- Flange width determines the overlap with surrounding shingles.
- Adequate width prevents water intrusion around the penetration.
- Minimum width is typically 4 inches in all directions.
Memory trick: Pipe's collar, four inches wide, keeps the water outside.