Which statement best describes the minimum window size rule for basement bedroom openings?

• A. The window must have both dimensions at least 45 cm
• B. The window must have at least one dimension at least 50 cm
• C. The window must have a minimum area with no dimension less than 35 cm
• D. The smaller dimension must be at least 38 cm, and the window must have a minimum area of 0.35 m^2

Answer: (D)

The key idea is safety: basement bedroom windows must be able to serve as an escape in an emergency, so the opening has to be large enough in two ways. First, the net clear opening area must meet a minimum size so a person can fit through—not just a tiny gap. Second, the opening can’t be too restrictive in one direction, so the smaller dimension must be at least a certain width. The combination of a minimum smaller dimension of 38 cm and a minimum area of 0.35 m^2 ensures the opening is both wide enough and large enough overall.

If you only require both dimensions to be above a moderate value, you could end up with an opening that is too small in area. If you require only one dimension to be large, you could still get an opening that isn’t big enough overall. And if you only insist on a minimum area with no restriction on the smaller dimension, you could have a long, very narrow opening that is impractical to use. The stated rule precisely balances both aspects, providing a usable escape passage. For example, a window around 38 cm by 92 cm yields about 0.35 m^2, meeting both requirements.