(1) Except as provided in Sentence (2) and Articles 9.8.4.5. and 9.8.4.5A., tapered treads shall have a run that,
(a) is not less than 150 mm (5-7/8") at the narrow end of the tread, and
(b) complies with the dimensions for rectangular treads specified in Table 9.8.4.1. when measured at a point 300 mm (11-13/16") from the centre line of the inside handrail.
(2) Tapered treads in required exit stairs shall conform to the requirements in Article 3.4.6.9.
(3) The depth of a tapered tread shall be not less than its run at any point and not more than its run at any point plus 25 mm .
Ontario Building Code - Volume 1, O. Reg. 332/12, Article 9.8.4.5. of Division B
9.8.4.5. Winders
A-9.8.4.5. Winders.
(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 (47 -1/4").
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