Penetrations in roof membranes are one of the most common sources of leaks. This article covers how to flash pipes, exhaust vents, and rooftop mechanical curbs using tested, reliable detailing methods and code-compliant materials.
Common Roof Penetration Types
- Plumbing vents and exhaust stacks
- Gas lines, conduits, and low-voltage penetrations
- HVAC equipment curbs and skylight frames
- Fall protection anchor points and solar panel supports
Flashing Strategy and Sequencing
- Install base flashing or pipe boot prior to roof membrane, sealing to deck or underlayment
- Wrap and lap membrane over base flashing collar or boot flange
- Use termination bars and sealant at vertical surfaces or large curbs
- Cap flash with pre-molded storm collars, metal hoods, or flashing kits depending on pipe type
Code and Warranty Considerations
Use manufacturer-approved accessories to avoid voiding membrane warranties. NRCA and IBC require all penetrations to be flashed per ASTM D1970 and membrane manufacturer guidelines. Support curbs and pipes independently to prevent deck movement from stressing seals.
Installation Quality Control
- Inspect field wraps around circular penetrations for wrinkles or tenting
- Check sealant bond and ensure correct bead size and coverage
- Use primer when required by membrane manufacturer at pipe boots and tape interfaces
- Photograph each penetration during installation for warranty submission
Test suspect penetrations using ASTM D5957 water intrusion testing if needed post-installation.
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