Part K Stair Calculator — Rise, Going, Pitch & Headroom

A private stair serves only one dwelling. AD K 2013 Table 1.1 allows a rise of 150mm to 220mm with a going of 220mm to 300mm, and note 1 caps the pitch at 42 degrees. Para 1.3 lets you pair any rise in that range with any going in that range. The 2R+G figure (twice the rise plus the going, 550mm to 700mm) is described in the table as the normal relationship between the two dimensions rather than as a limit, so this calculator reports it as a note and not as a failure. Note 2 adds one further figure for dwellings: external tapered steps and stairs that form part of the building need a going of at least 280mm.

42 degrees, and only for a private stair (Table 1.1 note 1). AD K 2013 sets no maximum pitch for a utility stair or a general access stair, because the rise and going ranges already cap them: a utility stair cannot be steeper than atan(190/250), about 37.2 degrees, and a general access stair cannot be steeper than atan(170/250), about 34.2 degrees. The only other pitch figure in the document is the 35 degree maximum for gangways to spectator seating areas in assembly buildings (para 1.4a). There is no 38 degree limit anywhere in AD K 2013.

2m on the access between levels, in all buildings, measured vertically from the pitch line (para 1.11 and Diagram 1.3). For a loft conversion in a dwelling where there is not enough space for that, para 1.13 and Diagram 1.4 allow reduced headroom of 1.9m over the half width of the stair, falling to 1.8m at the side. A flat 1.8m across the whole width is not what the diagram shows. In buildings other than dwellings, and in common areas of blocks of flats, means of escape routes need 2m clear headroom except in doorways (para 1.12).

In buildings other than dwellings, para 1.15 asks for a stair width of at least 1200mm between enclosing walls, strings or upstands, and at least 1000mm between handrails. Those are two different dimensions, and Appendix A defines stair width as the clear width between the walls or balustrades, so 1200mm is the one to compare a measured stair width against. A flight more than 2m wide should be divided into flights at least 1000mm wide (para 1.15c). For a stair inside a dwelling, AD K 2013 gives no minimum width at all: the only dwelling figure is 900mm, and only within the entrance storey where a severely sloping plot forces a stepped change of level (para 1.16). AD K 2013 also gives no width for a common stair in flats, because para 1.15 sits under a heading covering buildings other than dwellings. Means of escape widths come from Approved Document B (para 1.14).

Position the top of the handrail 900mm to 1000mm from the pitch line or floor, in all buildings (para 1.34a). Provide a handrail on both sides if the stairs are 1000mm or wider (para 1.34c). Guarding is a separate thing at different heights, taken from Diagram 3.1: in a single family dwelling, 900mm on stairs, landings, ramps and edges of internal floors, rising to 1100mm on external balconies and edges of roofs; in residential, institutional, educational, office and public buildings, 900mm on flights and 1100mm everywhere else, landings included, because those are fall-from-height positions. The graspable 32mm to 50mm circular handrail diameter comes from Diagram 1.13 through para 1.36g, which applies to buildings other than dwellings rather than universally.