What performance standards do windows have to meet in Ontario?
Windows, doors and skylights must conform to the North American Fenestration Standard, AAMA/WDMA/CSA 101/I.S.2/A440 (NAFS), and the Canadian Supplement CSA A440S1, with performance grades matched to the site's wind and rain exposure.
NAFS rates fenestration products for air leakage, water penetration resistance and structural wind load capacity, expressed as a Performance Class (R, LC, CW, AW) and Performance Grade. The Canadian Supplement translates a building's location, height and terrain into the minimum driving-rain wind pressure and design pressures the specified product must meet — so a window that is fine in a sheltered bungalow may fail the spec on an exposed high-rise. Energy performance (U-value, solar heat gain) is regulated separately under the energy efficiency requirements (SB-12 for houses, SB-10/Part 12 for larger buildings). Permit reviewers commonly ask for NAFS labels or test reports to be referenced on drawings.
Windows are tested and graded like appliances — for how much air they leak, how much wind-driven rain they keep out, and how much wind pressure they survive. Your job is to pick a grade that matches how exposed the building is.
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This page is provided for general information. Building code requirements depend on your specific project, occupancy and municipality, and code editions change. Always verify requirements against the current Ontario Building Code and confirm with your local building department.