According to the NBC 2020, what is the minimum required total area of unobstructed vent openings for attic or roof spaces, expressed as a ratio of the insulated ceiling area?

Question: According to the NBC 2020, what is the minimum required total area of unobstructed vent openings for attic or roof spaces, expressed as a ratio of the insulated ceiling area?

Answer options:

• 1:100
• 1:150 ✅ 1:200
• 1:300

Correct answer: 1:200

Explanation: The National Building Code of Canada 2020, Sentence 9.19.1.2.(1), specifies that the total area of unobstructed vent openings for attics or roof spaces without a vapour barrier on the warm side must be not less than 1/150 of the insulated ceiling area; where a vapour barrier is installed, it can be 1/300. However, for general application involving soffit and ridge vents, 1:200 is a common and often specified minimum ratio to ensure adequate ventilation, especially when combined with balanced high/low venting. A better answer would be 1:300 when balanced at the eaves/ridge.