Every bedroom needs a way out in a fire besides the door, and that's the job of an egress window. This matters most in basement bedrooms and legal suites, where an undersized window can make the room non-conforming and unsafe.
Minimum size
An egress window must provide a minimum unobstructed openable area — in the BC Building Code this is 0.35 square metres (about 3.8 square feet), with no dimension less than 380 mm (15 inches). That means a window can't be too tall and narrow or too short and wide to qualify, even if the area math works.
Sill height and access
BC doesn't set a hard maximum sill height, but it recommends the sill be no higher than about 1.5 m above the floor so an occupant can climb out — where it's higher (common in basements), build in a step or furniture below it. The opening must be operable from the inside without tools or special knowledge. For basement windows, a window well must give at least 760 mm of clearance in front of the window to climb into and out of, and deep wells may need a ladder.
Why it matters for suites
A basement bedroom without a compliant egress window isn't a legal bedroom, which affects insurance, rental legality, and resale. If you're finishing a basement or building a suite, plan egress early — enlarging a foundation opening later is expensive.