Cant Strips: Essential Components for Durable Flat Roofs in Vancouver
Flat roofs, valued for their modern aesthetic and space efficiency, are prevalent in Vancouver’s urban and residential buildings. However, their low slope (2–4%) makes them susceptible to water pooling and membrane stress, particularly at intersections with vertical surfaces like parapets or skylights. Cant strips—angled components that smooth the transition from horizontal roof to vertical wall—are critical for mitigating these risks, enhancing membrane longevity, and ensuring drainage. In Climate Zone 5’s wet, temperate climate (1200 mm rainfall, 85–95% RH), cant strips are indispensable for durable flat roofs. Simon Green Works integrates cant strips into every flat roof design, using building science to ensure resilience. This article explores their purpose, necessity, material options, compatibility, sizing, installation techniques, and Vancouver-specific considerations, providing a comprehensive guide for robust roof assemblies.
Purpose of Cant Strips
Cant strips, typically installed at roof-to-wall junctions, reduce the sharp 90° angle that roof membranes navigate, minimizing stress from thermal expansion, contraction, UV degradation, and moisture exposure. By creating a 45° transition, cant strips prevent membrane tears, voids, or adhesion failures, which can occur within 5–10 years without them, per Building Science Corporation. They also direct water away from seams, reducing leak risks in Vancouver’s high-rainfall environment. For thicker membranes, like 90 mil EPDM or 240 mil modified bitumen from SOPREMA (SOPREMA Bitumen), cant strips are critical to prevent cracking at stress points, ensuring a 20–30-year lifespan.
Necessity of Cant Strips
Omitting cant strips compromises flat roof integrity, particularly in Vancouver’s variable climate. Sharp 90° transitions strain membrane adhesion, especially under temperature swings (0–25°C) and relentless rain, leading to uplift forces and failures within years. A study by ASIRI Designs found that roofs without cant strips had a 70% higher leak rate at parapets. The cost of cant strips ($2–$5 per linear foot) is minimal compared to repairs ($10,000–$50,000), justifying their use even in budget projects. In Vancouver, where wet-dry cycles accelerate membrane degradation, cant strips are essential for compliance with BC Building Code detailing requirements, ensuring long-term durability.
Material Options and Compatibility
Cant strips are fabricated from various materials, each with specific properties: - Wood: Pressure-treated lumber, like ACQ-treated pine, offers durability but lacks flexibility, suitable for stable structures. - Perlite: Lightweight, heat-resistant composite from Blue Ridge Fiberboard (Blue Ridge Cant Strip), ideal for hot-applied bitumen membranes, withstanding 200°C application temperatures. - Rigid Foam: XPS or EPS, such as Kingspan GreenGuard (Kingspan GreenGuard), provides flexibility but is incompatible with PVC membranes due to plasticizer migration. - Metal: Durable but rigid, reserved for commercial applications due to cost ($10–$20 per linear foot).
Perlite and wood are preferred for Vancouver’s TPO and EPDM membranes from Firestone (Firestone TPO), while foam requires a Delta-MS dimple mat (Delta-MS) with PVC to prevent chemical reactions.
Sizing and Angles for Optimal Performance
Cant strips typically feature 45° angles to balance membrane stress and drainage. Sizes range from 19 mm x 19 mm to 150 mm x 150 mm, with 75 mm x 75 mm recommended for most Vancouver applications. Larger strips (100–150 mm) buffer thermal movement in parapets, while smaller ones suffice for minor curbs. Tapered edge strips, sloping from 0 to 50 mm over 150 mm, enhance drainage for short parapets. Proper sizing prevents pooling, critical in Vancouver’s rainy seasons, and ensures compliance with BC Building Code’s drainage requirements. Custom fabrication, using tools from Malco (Malco Tools), tailors strips to complex geometries.
Installation Techniques
Installation begins with a clean, primed deck, followed by a fully adhered membrane, such as Firestone TPO. Cant strips are mechanically fastened or adhered to the deck at parapet bases, with membranes lapped over them and sealed with Sika Everbuild tape (Sika Sealants). A mil gauge verifies membrane thickness (80 mil minimum), and electronic leak detection from Detec (Detec Systems) ensures integrity. In Vancouver, scheduling during dry windows prevents moisture entrapment, critical for long-term performance.
Vancouver-Specific Considerations
Vancouver’s Climate Zone 5 demands cant strips that enhance drainage and withstand humidity. Perlite or wood strips, paired with TPO or EPDM membranes, resist degradation, while foam requires protective mats with PVC. Local codes mandate robust detailing at parapets, with cant strips ensuring compliance. Seismic standards (0.46g) require secure anchorage, verified by engineers. Green roofs or roof decks, common in Vancouver, increase loads (200–500 kg/m²), necessitating larger strips. Regular maintenance—inspecting seams and clearing drains quarterly—is essential. Density bonuses ($100,000–$500,000) incentivize sustainable roofing, which our designs optimize.
Why Choose Simon Green Works?
Simon Green Works delivers flat roof solutions with meticulously integrated cant strips, ensuring durability and compliance in Vancouver’s challenging climate. Our building science expertise creates leak-free, energy-efficient assemblies. Ready to enhance your flat roof? Contact us for a tailored consultation.
Sources
This article draws on insights from Sharif Asiri’s article, “What Are Cant Strips? (and Why You Need Them On A Flat Roof),” published by ASIRI Designs (What Are Cant Strips? (and Why You Need Them On A Flat Roof)). Additional perspectives are informed by “CANT STRIP & TAPERED EDGE” from Blue Ridge Fiberboard (CANT STRIP & TAPERED EDGE).