Should timber cladding be flame retardant treated?
Depending on its situation, UK Building regulations may stipulate that timber cladding is protected with a suitable flame retardant product. This can be when a boundary falls within one metre of the edge of the building or where cladding is used on multi-story buildings. It is advisable to check with the Building control office.
Visit the Government website to get a copy of Approved Document B on fire safety and any relevant amendments.
TDCA recommends using flame retardant products that are applied in a controlled, factory process. If a flame retardant treated timber is to be utilised, it’s imperative to ensure:-
- the treatment is approved, leach resistant and suitable for external use
- the treatment is compliant and is supported by a relevant, full classification report that identifies Euroclass rating specific to timber species and thickness being used
- the flame retardant is compatible with any subsequent products that are to be used e.g. coatings. Reputable suppliers offer to factory apply compatible coatings which means you are dealing with a single supplier if issues arise.
2021: Industry Statement on the performance of wood cladding in a fire
The outcome of the UK government’s assessment last year of the use of different cladding materials in the wake of the Grenfell tragedy confirmed that timber, where necessary enhanced with flame retardant, remains fit for purpose where the upper floor level of a building is less than 18m above ground (Building Regulations England).
In all situations where Building Regulations stipulate a particular reaction to fire performance level for materials on the external face of a multi-storey residential building below this level, then those performance levels must be complied with.
However, Building Regulations guidance does not always stipulate a particular reaction to fire performance for cladding and/or balconies on buildings where the upper floor level is less than 18m above ground. In such circumstances, so as to provide consistency, insurance and peace of mind against unforeseen circumstances, an independent, professional fire risk assessment which takes into account the building design, use, materials and location is essential at the project design stage. Indeed, this has been a principle embodied in the CDM Regulations for some years which has very recently been reinforced by MHCLG in a circular letter to Building Control in England & Wales.
Such an assessment may demonstrate that, by means of careful design and component specification, flame retardant treatment is unnecessary in the particular circumstances. However, following recent reviews and from industry feedback on new projects, the Confederation of Timber Industries (of which TDCA is a member) recommends that all such timber based cladding and balcony components should be treated using a quality assured factory-applied flame retardant to Euroclass B, unless shown not to be necessary by an appropriate risk assessment process.
Timber remains an excellent material for manufacture and construction, but risk assessment, specification and detailing are paramount to ensuring safety whatever the build method.
Cladding Compliance Toolkit
This excellent interactive web-based tool by RISC Authority is designed to help specifiers understand the fire rating requirements of external building cladding systems.
It’s extremely easy to use with options for each of the regions of the UK in which the building may be sited. It provides technical background at each stage, as the user works through the questions and at the end provides a downloadable report summarising the conclusions for the particular project.