Timber stair treads flex when stairs used

Cause

Timber not thick enough for span (stair width)

Repair

  • treads should generally span no more than 1.2 m between strings and should be at least 50 mm thick
  • where an existing tread is in good condition but too thin for the span, add an additional stiffening member (SG 8 wet in service H4-treated) under the tread and fix at each end to the string
  • if the stair is being rebuilt, add mid-span strings for support with wide stairs. Sagging and deflection will be minimised by adding strings at 1.2 m centres.

Cause

Stair string not big enough for the stair 

Repair

  • install additional string to the centre of the stair or steps where possible or flitch an addition string to the existing
  • add additional support H4-treated posts at the centre of each string
  • the best long-term solution will be to rebuild the stair with strings of appropriate size. You can find guidance for building external stairs here and guidance on the design of internal and external stairs in BRANZ Bulletin BU625 Stair design.