BCAB 1792 - Stair nosings and rakeback, Article 3.4.6.8.

Stair nosings and rakeback, Article 3.4.6.8.

Project description

The project is a new exit stair in an existing medium hazard industrial occupancy building to which Part 3 of the 2012 British Columbia Building Code applies. The new exit stair is proposed to have steps with a rise of 180 mm and a run of 280 mm. It will be constructed with closed vertical risers (no rakeback) and with no nosings protruding beyond the face of the risers.

Applicable Code requirements

Sentence 3.4.6.8.(2) states:

2) Steps for stairs referred to in Sentence (1) shall

• a) have a rise between successive treads not less than 125 mm and not more than 180 mm,
• b) have a closed riser, and
• c) have
  • i) a riser with a rakeback of not more than 38 mm, or
  • ii) the underside of the nosing with an angle of not less than 60° from the horizontal.

Decision being appealed (Local authority’s position)

The local authority has determined that vertical risers are not permitted.

In order to comply with Sentence 3.4.6.8.(2), the stair risers must have either a rakeback or extended nosing.

Appellant's position

The appellant contends that a rakeback of 0 mm complies with Subclause 3.4.6.8.(2)(c)(i) and a nosing with an underside angle of 90° complies with Subclause 3.4.6.8.(2)(c)(ii), and concludes that a vertical riser complies with the Code.

Appeal Board Decision #1792

It is the determination of the Board that the subject stairs comply with Sentence 3.4.6.8.(2).

Reason for decision

The intent of the Code is to limit excessive rakeback, and therefore 0 mm (vertical) is compliant. The Code does not require a nosing, but rather when a nosing is provided, there are specific provisions.

The Board does acknowledge that the Code language is not as precise as it could be.

Lyle Kuhnert
Chair, Building Code Appeal Board