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The National Construction Code (NCC) Volume Two – Housing Provisions contains provisions for stair construction in Class 1 buildings. Note that there are no Australian Standards for residential stair construction.
All stairs must comply with the NCC Performance Requirements. This can be achieved by building a stair in accordance with the Deemed-to-Satisfy Provisions set out in the NCC that requires:
|Table 1 (extract from the NCC Volume Two)|
|Riser and going dimension (mm) for private stairways|
|Types ||Riser (R)||Going (G)||Slope relationship (2R+G)|
Note: BCA Volume One has a minimum going of 250mm for public stairways.
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The purpose of NCC stair riser and going dimensions is to achieve constant stair tread dimensions deemed safe for people to walk up and down. This minimises the risk of people overstepping during descent on uneven stairs (due to short goings) and tripping on ascent (due to high risers).
However, NCC clause 188.8.131.52(a)(iii) accounts for conditions such as movement of materials due to atmospheric moisture changes or minor deviations related to variations in materials which affect finished stair dimensions.
Some state governments (including NSW and Victoria) have also published specific documents that may be used by the builder and the consumer to gauge tolerances for some building matters. The guides all includes tolerances for stair construction. HIA also publishes the Guide to Materials and Workmanship for Residential Building Work [LINK to the new page relating to the Guide], which provides a tolerance for stair construction.
A tolerance of up to 5mm from the nominated dimensions in the contract documents is considered acceptable to allow for the variation in behaviour of timber caused by atmospheric moisture changes. This would generally relate to external stairs.
The top and bottom risers may be varied to allow for the installation of floor finishes nominated in the contract documents. This variation is to provide uniform and constant riser height throughout the stair after installation of the nominated floor finishes. This also applies to first and last risers of concrete stairs. This tolerance is not to be applied to allow for poor construction practice.
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