28 January 2019

Updated WIS: Timber joist and deck floors – avoiding movement

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TRADA's updated WIS Timber joist and deck floors avoiding movement gives guidance specifically intended to minimise problems of movement and noise in timber floors. Today nearly all intermediate floors in domestic-scale buildings have timber joists with a timber-based sheet material deck, so this simple but insightful guidance can make a big impact.


Incorrect specification or neglect of good site practice can both affect long-term performance, leading to problems of movement and noise in service. While these problems do not generally result in serious structural defects, they can have substantial consequences for the occupants of the dwelling. It only takes movement of less than 0.5mm to cause significant noise, and the effects can be overwhelming: not only is the cost to builders for remedial action high, it can greatly inhibit occupants’ productivity and eventually impact upon wellbeing.


The WIS Timber joist and deck floors avoiding movement therefore serves as a checklist of best practice, ensuring timber floors give continuing satisfactory performance. Aimed at designers and site supervisors, it provides guidance on moisture content and joist shrinkage, notching and drilling, strutting and noggings, and much more.


The WIS was reviewed in December 2018 and updated to include:

  • a more in-depth discussion of shrinkage
  • a section on incidents of floor squeaks, creeks and cracking noises
  • discussion of site protection systems and the benefits of clipboard screws
  • definitions of strutting, blocking and noggings
  • additional guidance on i-joists, metal web joists, board types and site wetting


Find out more with TRADA publications:


Members can download a free copy of the WIS Timber joist and deck floors avoiding movement. WIS sheets are available to non-members too – purchase a PDF or a hardcopy at the TRADA Bookshop.



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No timber question is too big or too small for TRADA’s friendly panel of experts. Check out our answers to your most frequently asked questions on topics such as cladding, decking, fire doors and much more. Alternatively, members can pick up the phone or email us for free, confidential advice on +44 (0)1494 569601 or advisory@trada.co.uk.