Cant

Cant is an angled surface or edge in construction, often used to direct water runoff or for aesthetic design. The most common application is a cant strip — a triangular piece of material placed where a flat roof meets a vertical surface like a parapet wall.

Where Cants Are Used

• Flat roofing: Cant strips (usually wood, foam, or perlite) are placed at the base of parapet walls and curbs. They create a 45-degree transition that prevents roofing membrane from making a sharp 90-degree bend, which would crack and leak over time.
• Concrete work: Cant edges on concrete steps, curbs, and ledges provide a beveled edge that resists chipping and looks cleaner than a sharp corner.
• Timber framing: Canted beams or posts are set at an angle for structural or decorative purposes, commonly seen in timber-frame homes and pavilions.
• Masonry: A cant brick is a brick with one corner cut at an angle, used for window sills, copings, and decorative coursework.

Practical Example

A roofing crew is installing a TPO membrane on a commercial flat roof. At every parapet wall, they set a 4” x 4” foam cant strip before running the membrane up the wall. Without the cant, the membrane would have to make a sharp 90-degree turn at the base of the wall — a guaranteed failure point within a few years. The cant strip creates a gradual slope that the membrane can follow smoothly, and the sealant adheres properly to both surfaces.

Why It Matters

Skipping cant strips on a flat roof is one of the most common installation mistakes. It looks like a small detail, but that 45-degree transition is what keeps water from pooling at the wall-to-roof junction and working its way under the membrane.

For related roofing details, see our built-up roofing and single-ply membrane guide.