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Carpenter Red Seal Exam Prep · Question

The Building Code requires a minimum unit run of 210 mm for residential stairs. Considering a comfortable unit rise of 180 mm and minimum nosing (projection from the back of the tread) for closed-riser stairs, what would be suitable tread depth?

NBC 2020 specifies a minimum tread depth of 210 mm. When a nosing of 25 mm (maximum allowed) is added, the tread needs to be 210mm (min run) + 25mm (nosing proj

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Question: The Building Code requires a minimum unit run of 210 mm for residential stairs. Considering a comfortable unit rise of 180 mm and minimum nosing (projection from the back of the tread) for closed-riser stairs, what would be suitable tread depth?

Answer options:

  • 210 mm ✅ 235 mm
  • 200 mm
  • 250 mm

Correct answer: 235 mm

Explanation: NBC 2020 specifies a minimum tread depth of 210 mm. When a nosing of 25 mm (maximum allowed) is added, the tread needs to be 210mm (min run) + 25mm (nosing projection) = 235mm total for safe footing.

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