NHBC Standards 2023 Cl 6.4.9 Timber joists – clarification on deflection limits

Following several enquiries and a meeting held between floor joist manufacturers and NHBC Standards, Innovation and Research in January 2023, it is necessary for us to advise as follows: 

• Within the current bulleted Guidance of ‘no more than 0.003 x the span for the combined bending and shear based on the total dead and imposed loads, with a maximum deflection of 14mm where strutting is provided, or 12mm where strutting is not provided’, ‘maximum deflection’ should be taken as applying to the instantaneous deflection, not the final deflection.

For existing plots where foundations were concreted prior to 1 January 2023, previous NHBC standards apply, and the new Guidance does not need to be met.

For new and existing plots where the foundations have been concreted after 1 January 2023, but the floors have been supplied, stored or ordered prior to this date, acceptance of floors designed to previous NHBC Standards will be accepted until 30 June 2023.  From 1 July 2023, all new floors should meet the new requirements.