9.8.4.3 — Dimensions for Tapered Treads

(1) Flights used as an exit shall consist solely of, (a) straight flights, or (b) curved flights complying with Sentence (2). (2) A curved flight used as an exit shall have, (a) a handrail on each side, (b) treads with a minimum run of 240 mm, (c) treads with a run that conforms to Article 3.4.6.8. when measured at a point 300 mm from the centre line of the inside handrail, and (d) an inside radius that is not less than twice the stair width. (3) Tapered treads shall have a consistent angle and uniform run and rise dimensions in accordance with the construction tolerances described in Article 3.4.6.8. when measured at a point 300 mm from the centre line of the inside handrail. (4) All tapered treads within a flight shall turn in the same direction.

(1) Stairs within dwelling units are permitted to contain winders that converge to a centre point provided, (a) the winders turn through an angle of not more than 90°, (b) individual treads turn through an angle of not less than 30° or not more than 45°, and (c) adjacent winders turn through the same angle. (2) Where more than one set of winders described in Sentence (1) is provided in a single stairway between adjacent floor levels, such winders shall be separated in plan by at least 1 200 mm.

(1) Spiral stairs shall have, (a) handrails on both sides, the outer handrail being not less than 1 070 mm high, (b) a clear width not less than 660 mm between handrails, (c) risers that are not more than 240 mm high, (d) treads that, (i) are a minimum of 190 mm deep at a point 300 mm from the centre line of the inside handrail, (ii) have a consistent angle and uniform dimension, and (iii) turn in the same direction, and (e) a clear height not less than 1 980 mm. (2) Spiral stairs conforming to Sentence (1) are permitted to be used as the only means of egress where they serve not more than 3 persons. (3) Except as permitted by Sentence (2), spiral stairs shall not serve as an exit.