Can timber be fire-treated?

Timber is an increasingly popular material among architects and specifiers for cladding, architectural façades and brise soleil.

Why should I choose a timber lookalike instead of the real thing?In a nutshell:

  • Timber can be treated to be Class B fire retardant
  • Flame retardant Class B timber may be suitable for many types of façade projects
  • Treatment should always be applied by a specialist in a controlled, factory setting
  • Fire treatment prevents oxygen from reaching the timber, slowing the spread of fire
  • Fire-treated timber will weather naturally but is not usually suited for other coatings

It’s versatile and can look great as an architectural façade, and is considered an environmentally friendly product if sourced from sustainable stocks. But there are concerns about its fire retardancy after high-profile tragedies and new, more stringent fire safety regulations. So, what can be done?

Can timber be made safer

Wood has been used as a fuel since the dawn of history, So, the idea of non-combustible timber sounds like a contradiction. It’s true, timber will never achieve a Class A fire-retardancy rating – but Class B may be possible with the addition of a flame retardant.

Significantly, flame retardant Class B timber may be fit for purpose for many applications in compliance with building regulations. However, it’s a complex question and you should seek advice from a specialist coating applicator or façade company.

What does the fire retardancy process look like?

Treatment should always be applied in a controlled, factory setting to the raw materials – spraying or coating the finished product in situ will be unreliable. Certified treatments are applied in a controlled factory environment, where the timber is impregnated with a fire-retardant chemical under pressure.

How does fire treatment work?

The treatment prevents oxygen from reaching the timber, slowing the rate of ignition and reducing the spread of fire. This means that people will have more time to evacuate, and less damage may occur before the fire is extinguished.

Does fire retardant timber look different?

This is a concern for architects – timber is usually chosen for aesthetic reasons. The good news is that while certain wood species may darken during treatment, it will naturally fade again with weathering (without affecting its safety). However, the weathering process may also result in cracks or splits in the timber. For peace of mind, its best to talk to your cladding or façade specialist, and ask for samples.

What about coating treated timber?

Fire retardant timber doesn’t need any further preservation treatment. That’s the good news. However, certain aesthetic paints and stains may not adhere to the treated timber and may not actually be fire retardant in themselves. So, generally speaking, coating treated timber is a non-starter.

What building standards to look out for

Fully certified fire-retardant timber must be tested to meet Euro Class B or Class C according to the EN 13501-01 standard. The standards indicate limited (or very limited) spread of fire. You should also look out for the ‘S’ (smoke) and ‘D’ (flaming droplets) values in a fire safety report. The lower the number the better, so s0 and d0 will offer the greatest protection.

What next?

There’s no doubt that protecting buildings against fire is a worry – but it doesn’t need to preclude the use of timber. Yes, it’s a complex subject, but support and advice is available from specialist classing and façade companies. Alternatively, why not consider advanced powder coatings that can make non-combustible aluminium look like timber?

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