What are the attic access hatch requirements in Ontario?
An access opening is required to attics and roof spaces of significant size, generally those at least 600 mm (24 in.) high over a substantial area. The hatch must be roughly 0.32 m² in area with no dimension less than about 545 mm (21.5 in.), and must remain accessible.
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The hatch exists so insulation, ventilation, roof leaks and wildlife issues can be inspected without opening the ceiling. In practice, verify the rough opening clears the required dimension after trim and weatherstripping, since finished openings often shrink below minimum. Energy compliance adds its own layer: the hatch should be insulated to a level compatible with the ceiling and weatherstripped, because an uninsulated plywood lid is a significant heat leak and a condensation spot. Avoid locating hatches in closets so tight that a ladder cannot be set up, a common practical complaint from inspectors and trades.
Any real attic needs a hatch big enough for a person, roughly 545 mm across at minimum, so it can be checked and maintained. Make sure the lid is insulated and weatherstripped, and put it somewhere you can actually stand a ladder.
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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.