What is the minimum stair tread depth for a residential building under the National Building Code?

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## Minimum Stair Tread Depth for Residential Buildings Under the National Building Code

The minimum stair tread depth for a residential building under the National Building Code of Canada (NBC) 2020 is **255 mm (10 1/16")** for private stairs serving dwelling units.

### Understanding "Private" vs. "Public" Stairs

The NBC distinguishes between two stair types, and the requirements differ between them:

**Private stairs** serve single dwelling units, houses with a secondary suite (including their common spaces), or garages that serve those occupancies. For these stairs, the run shall be a minimum of 255 mm (10 1/16") and a maximum of 355 mm (13 15/16") . Since tread depth shall be not less than the run and not more than the run plus 25 mm (1"), the minimum tread depth for private stairs is also **255 mm (10 1/16")** .

**Public stairs** (all stairs that are not private or service stairs) have a minimum run of 280 mm (11") with no maximum, meaning the minimum tread depth is **280 mm (11")** .

### Key Companion Dimensions

For private stairs, the rise shall be a minimum of 125 mm (4 15/16") and a maximum of 200 mm (7 7/8"). For public stairs, the maximum rise is reduced to 180 mm (7 1/16") with the same 125 mm (4 15/16") minimum .

### Nosing Requirements

Regardless of stair type, the top of each tread nosing shall have a rounded or beveled edge extending not less than 6 mm and not more than 14 mm (approximately 1/4" to 9/16") measured horizontally from the front of the nosing. Where resilient material covers the nosing, this minimum may be reduced to 3 mm (1/8") .

### Uniformity and Tolerance

All rectangular treads within a flight shall have a uniform run, with a tolerance of no more than 5 mm (3/16") between adjacent treads and no more than 10 mm (3/8") between the deepest and shallowest treads in the entire flight .

### Quebec Difference

Quebec adopts the NBC 2020 with provincial amendments. The tread and run requirements above are consistent between the NBC 2020 and the Quebec Construction Code 2020, with the same minimums applying .

In summary, for a typical residential stair (private stair), designers and builders must ensure each tread is at least **255 mm (10 1/16") deep**, measured nosing to nosing, and no greater than 380 mm (15") deep (run plus the 25 mm nosing allowance).

What is the minimum stair tread depth for a residential building under the National Building Code?

Minimum Stair Tread Depth for Residential Buildings Under the National Building Code

Understanding "Private" vs. "Public" Stairs

Key Companion Dimensions

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