A building inspector observes a stair with a cumulative variation in riser height of 15 mm over a flight of stairs. According to the NBC 2020, how does this cumulative variation compare to the allowed limit?

Question: A building inspector observes a stair with a cumulative variation in riser height of 15 mm over a flight of stairs. According to the NBC 2020, how does this cumulative variation compare to the allowed limit?

Answer options:

• It is acceptable, as the maximum cumulative variation permitted is 19 mm. ✅ It is not acceptable, as the maximum cumulative variation permitted is 13 mm.
• It is acceptable, as the maximum cumulative variation permitted is 25 mm.
• It is not acceptable, as there should be no cumulative variation.

Correct answer: It is not acceptable, as the maximum cumulative variation permitted is 13 mm.

Explanation: The NBC 2020 permits a maximum cumulative variation of 13 mm in riser height or tread depth in any flight of stairs. A 15 mm cumulative variation would therefore not be acceptable.