Where Should Ice & Water Membrane Underlayment Be Installed?
Ice and water membrane underlayment is one of the most important protective layers in a roofing system, especially in the Ottawa Valley where harsh winters, ice dams, and heavy snowfall are common. This self-adhering membrane creates a watertight barrier that prevents water from penetrating your roof deck.
Key Installation Locations
Ice and water membrane should be installed in areas of your roof that are most vulnerable to water infiltration:
- Eaves (Roof Edges) – The most critical location. Building codes in Ontario typically require ice and water membrane to extend at least 36 inches (approximately 3 feet) from the edge of the roof, or 24 inches past the interior wall line, whichever is greater. This protects against ice dam damage.
- Valleys – Where two roof slopes meet, water naturally concentrates. A full width of membrane should run the entire length of every valley.
- Around Penetrations – Plumbing vents, exhaust fans, chimneys, and skylights all create potential leak points. Membrane should be applied around all roof penetrations.
- Chimneys & Walls – Where the roof meets a vertical surface like a chimney or a wall, membrane provides extra protection behind the step flashing.
- Low-Slope Areas – Any section of roof with a pitch below 4:12 benefits from additional membrane coverage, as water moves more slowly and has more opportunity to find its way under shingles.
Why It Matters in the Ottawa Valley
Our region's freeze-thaw cycles create the perfect conditions for ice dams. When snow melts on your roof and refreezes at the eaves, it can force water back up under your shingles. Without proper ice and water membrane, this water can seep through the roof deck and cause interior damage to ceilings, walls, and insulation.
Full Roof Coverage
While code requires membrane only in vulnerable areas, some homeowners choose to install it across the entire roof deck for maximum protection. This is particularly common on lower-pitched roofs or homes in areas prone to wind-driven rain.
Professional Installation
Proper installation of ice and water membrane requires experience and attention to detail. The membrane must be applied to a clean, dry deck and properly lapped at seams to create a continuous barrier. At McKay Roofing, we ensure every installation meets or exceeds Ontario Building Code requirements. Contact us to discuss your roofing project.