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BRANZ Guideline February 2012 stair widths

Building Code compliance document D1/AS1 does not specify a width for common or main private stairways (the most common stairway applicable within residential buildings) but recommends no less than 850 mm.

When designing stairs, factors to consider are the design parameters given in D1/AS1 for:

  • riser and going dimensions to provide safe stairs to use
  • acceptable stair projections
  • open risers (when used)
  • handrail heights and dimensions
  • landings
  • minimum headroom
  • minimum widths when forming part of an access route
  • barriers complying with Building Code clause F4 when there is a fall distance of 1 m or more
  • clearances at doors accessing onto or off the stair
  • curved stairs
  • winders
  • tread visibility or definition.

It is also important to consider:

  • whether furniture can be moved between building levels that are only accessible by stairs
  • the slip resistance of the stair treads to ensure that stairs are safe to use.

D1/AS1 also gives the design parameters for accessible and service ramps – slope, width, landings, slip resistance, and so on.