S3.4 – S3.10SS3.4 The width of a stair, measured between handrails and clear of obstructions, must be at least 1 metre,except -a. the width of a private stair may reduce to at least -i.900mm where it is within the accessible storey, orii.600mm where it serves only sanitary accommodation and/or one room, other than a livingroom or kitchen, oriii.800mm elsewhere; andb. stringers and newels may each project not more than 30mm into the width; andc. a stair lift projecting into the width may be fitted to a stair within a dwelling.Note::There are additional stair width requirements for escape stairs in Part E.S3.5 The aggregate of the going and twice the rise must be at least 550mm and not more than 700mm.S3.6 A flight must have uniform rises, each at least 75mm.S3.7 The depth of a tread must not be less than the going.S3.8 In a flight with open rises the treads must overlap by at least 16mm. Any opening between adjacenttreads in a flight in a building of purpose group 1 or 5 or purpose sub-group 2A must be small enoughto prevent the passage of a 100mm sphere.S3.9 In a straight flight, or in that part of a flight which is straight, the going measured along the centre lineof the flight must be uniform.LENGTH OF FLIGHTSS3.10 A flight must have -a. not more than 16 rises; andb. at least 3 rises,except -there may be less than 3 rises -i.between an external door of a building and the ground, balcony, conservatory, porch orprivate garage; orii.in a stepped ramp; oriii.wholly within an apartment within a dwelling; oriv.wholly within sanitary accommodation within a dwelling; orv.between a landing and an adjoining level where the route of travel from the adjoining levelto the next flight changes direction through 90 degrees.Amdt: December 1999 12S