29 October 2018

Updated WIS: Performance of fire-resisting timber-based doorsets

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Fire-resisting doorsets are required to be able to contain a fully developed fire, to facilitate escape of a building’s occupants and allow fire-fighting, and to protect the structure from the effects of fire. Resistance to fire, expressed in terms of time – ‘fire resistance time’ – is therefore imperative for doorsets. This fire resistance time is determined by a test in which a doorset is exposed to a ‘standard’ fully developed fire in a test furnace until failure occurs according to certain criteria; this ‘standard’ fire condition is defined by the relationship between the duration of the fire and the temperature reached.


These tests are necessary because it is not possible to identify fire-resisting doorsets simply by weight and thickness. There is no exact minimum specification since any detail that can be proven to work with that particular design can be used. Increasingly, new materials and methods of construction have also led to the production of thinner and lighter fire-resisting doors.


Many factors can contribute to a reduced fire resistance time, such as faults or changes made to a doorset at the installation stage. The revised WIS Performance of fire-resisting timber-based doorsets is intended to guide architects, quantity surveyors, building surveyors, building control officers, fire prevention officers and builders through the various performance requirements for timber fire-resisting doorsets and makes recommendations on their specification. A full list of changes can be found below.


The WIS includes detailed guidance on the following:

  • Fire resistance time
  • Performance
  • Regulation requirements
  • Demonstrating performance
  • Doorset specification
  • Doorset design
  • Installation
  • Doorset variations
  • Maintenance


The WIS was reviewed in October 2018 and updated to make the following changes:

  • Elaboration of advice on meeting requirements for BS 476-22:1987 or BS EN 1634-1.
  • Advice on doorset design amended to reflect changing materials and methods of construction.
  • Additional detailed advice on gaps and how these can pass or fail integrity tests.
  • Discussion on evaluating variations (i.e. when modifications/changes have seriously altered the proven fire performance) when additional tests are not possible, and advice when such modifications will require additional testing.
  • Additional advice on glazing.
  • Advice on modifications to the doorframe updated to show that not all hardwoods are permissible for an FD60 doorset.


Find out more with TRADA publications:


Members can download a free copy of the WIS Performance of fire-resisting timber-based doorsets. WIS sheets are available to non-members too – purchase a PDF or a hardcopy at the TRADA Bookshop.



Lewis Taylor, TRADA's Timber Frame Consultant, is talking fire performance requirements for timber cladding and structural walls at the Better Timber Buildings conference on 15 November in London. Find out more