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Last edited 28 Sep 2020
Regulations for the design and construction of stairs are set out in Part K of the building regulations, and compliant designs are described in Approved Document K - Protection from falling, collision and impact.
The leading edge of the tread is described as the ‘nosing’. In buildings other than dwellings, the nosing should be visually contrasting, and a suitable tread nosing profile, should be used. See nosing for more information.
In buildings other than dwellings, risers should not be open to avoid feet or walking aids being caught underneath the tread during ascent, possibly causing a fall or giving occupants a feeling of insecurity. For dwellings, steps may have open risers if treads overlap by a minimum of 16 mm and steps are constructed so that a 100 mm diameter sphere cannot pass through the open risers.
A tapered tread is a step in which the going reduces from one side to the other. Where stairs have tapered treads, consecutive treads should use the same going. If a stair consists of straight and tapered treads, the going of the tapered treads should not be less than the going of the straight treads.
Alternating tread stairs are stairs with paddle-shaped treads where the wide portion is on alternate sides on consecutive treads. In dwellings, alternating tread stairs may only be used in loft conversions where there is not enough space for conventional stairs and where the stair is for access to only one habitable room and, if desired, a bathroom and/or a WC (although this must not be the only WC in the dwelling).
Alternating tread stairs should; make alternating steps uniform with parallel nosings, have slip-resistant surfaces on treads, have tread sizes over the wider part of the step in line with the table above, should provide a minimum clear headroom of 2 m, should be constructed so that a 100 mm diameter sphere cannot pass through the open risers and should comply with the diagram below.
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