Cant Strip - Roof Base Flashing Installation Guide
A cant strip is a beveled strip installed at a roof or wall transition to ease the angle where roofing turns up over flashing or parapet surfaces.
What It Is
A cant strip removes the sharp 90-degree corner at the base of a wall, curb, or parapet so roofing felts, modified bitumen, or membrane materials can transition more smoothly. By softening that bend, it reduces stress on the roofing material and helps prevent splitting, fishmouths, and premature wear at the change in plane.
Cant strips are usually made from wood fiber, treated wood, perlite, or compatible insulation materials depending on the roof system. They are a small component, but they matter because membrane failures often start at corners and base flashings.
Where It Is Used
Cant strips are used on low-slope roofs at parapet walls, equipment curbs, skylight curbs, roof hatches, and any location where the roof membrane turns up vertically. They are common in modified bitumen, built-up roofing, and some single-ply assemblies.
How to Identify One
A cant strip is usually hidden once the roofing is complete, but it may be visible during reroofing or at unfinished roof edges. It appears as a triangular or beveled strip set along the base of a vertical transition.
Replacement
Replacement usually happens during reroofing or flashing repair because the roofing materials above it have to be lifted to access it. If the strip is crushed, rotten, missing, or incompatible with the roof system, it should be replaced before the new membrane or base flashing is installed.
Frequently Asked Questions
Cant Strip — FAQ
- What does a cant strip do on a roof?
- It eases the angle where the roof turns up a wall or curb so the roofing material does not have to bend sharply. That reduces stress and helps the flashing last longer.
- Is a cant strip required on every roof?
- Not on every roof type, but it is common and often expected where built-up or membrane roofing transitions at a sharp base angle. The roof system and manufacturer details determine when it is needed.
- Can a missing cant strip cause leaks?
- Yes. Without it, the roofing membrane can crack, wrinkle, or pull away at the base flashing, which creates a vulnerable leak point.
- What is a cant strip made of?
- Common materials include wood fiber, treated wood, insulation board products, or other materials approved for the roof assembly. The right choice depends on the membrane system and exposure conditions.
- Can a cant strip be added during a roof repair?
- Yes, but the surrounding flashing and membrane layers usually have to be opened up to install it correctly. It is easiest and most reliable to address during reroofing or larger flashing repairs.
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