What is ice and water shield?
A self-adhering synthetic membrane applied to roof decking at eaves, valleys, and penetrations to block water infiltration from ice dams and wind-driven rain.
Ice and water shield is a self-adhering rubberized asphalt or synthetic membrane rolled out and pressed directly onto roof decking before shingles are installed. It creates a waterproof barrier that blocks water from flowing under shingles when ice dams form at eaves or when wind-driven rain pushes water upslope toward ridgelines.
Contractors install it along the lower edges of roofs (typically the first 3 to 6 feet from the eave), in valleys where water concentrates, and around roof penetrations like vents, skylights, and flashing. The membrane self-seals around nail holes and overlaps, which mechanical fasteners alone cannot achieve.
In Ontario, the building code requires ice and water shield at eaves and in valleys on all residential roofs. This requirement reflects the province's freeze-thaw cycles and exposure to ice dam conditions during winter months. Proper installation protects attic framing, insulation, and interior walls from water damage that can lead to rot and mold.
When hiring a roofing contractor for installation or replacement, ensure they specify ice and water shield in the work scope and confirm placement meets code requirements for your property.