Spotlight on fire-retardant cladding

The concept of cladding and whether timber cladding should be fire retardant is a topic that’s easily confused. Over the past few years, fire-retardant cladding has been a hot topic after the tragedy of Grenfell Tower in west London.

A tragedy such as that raises the question: should all timber cladding be fire retardant treated? The verdict is that there are defined requirements to meet, but it’s always best to look to the professionals for guidance.

There are varying factors for the use of fire-retardant timber cladding, all of them have been carefully outlined by UK Building regulations. A copy of which, the Approved Document B on fire safety, is available on the Government’s website. This document is the updated version and became available in May 2020.

When using the Euroclass EN13501-1 classification system, any major component part of the cladding zone must be A2 or A1 rated. A1 describes products that have no contribution to fire at any stage and A2 describes products that have no significant contribution to fire at any stage Products rated from B to F are not allowed.

The Government’s Approved Document B stipulates that timber cladding is to be protected with a suitable fire-retardant product when a boundary falls within one metre of the edge of the building or where cladding is used on a multi-level building.

Therefore, buildings where the upper floor level exceeds 18m above external ground level must only use non-combustible external cladding. This tends to be commercial properties and high-rise dwellings where timber cladding is very rarely used. Timber cladding tends to be a more popular choice for residential dwellings or low rise.

Why timber remains an excellent material for construction?

It’s important at this point to highlight that while timber is indeed a combustible material, in construction it has significant insulating properties and burns in a slow, predictable and measurable way. Charring is fast, but as the char depth increases it provides a stronger protective layer to the timber, slowing the overall combustion rate. The new wave of high rise buildings are being built using timber for their structure instead of steel, as well as already tried and tested glulam beams structures you see everywhere. As @TRADA_ says, “Timber in construction has undergone something of a renaissance, led by the desire to use more environmentally-friendly materials and to reduce construction costs.”

We can’t stress enough that timber remains an excellent construction material, including in the use of cladding. If you use a reputable designer and supplier, ensure a thorough risk assessment, along with thorough specification, you’ll be ensuring safety whatever the build.

Timber cladding fire retardants

Timber cladding can be easily protected from fire by the application of flame-retardant chemicals. These can be applied by an impregnation process, like a preservative treatment, using high pressure tanks or surface applied with brushes either on site or in controlled factory conditions. For external use, a leach-resistant type must be used.

Flame retardant chemicals generally work by reducing the surface spread of flame, heat, and smoke release, providing vital extra time for a safe escape.

Flame retardant treatments enhance the ‘reaction to fire’ properties of wood and wood-based materials. This reduces ignitability and the spread of flame, thus slowing down the development of the fire and giving occupants time to escape and for the fire to be extinguished.

Factory application of a flame-retardant treatment prior to installation ensures all faces of the timber or board product can be protected, offering a safer, low maintenance solution. It is therefore important to treat and seal all board ends cut on site.

Euroclasses

Up until recently different EU countries had differing methods for testing and classifying the Reaction to Fire performance of construction materials. For manufacturers to be able to sell their products in particular countries, they would have to carry out multiple tests. So, the introduction of a single classification system across the EU member states was a welcomed change that has meant manufacturers and the construction industry as a whole, can use a common method for comparing the Reaction to Fire performance of construction products.

Standardised through the use of EN 13501-1, testing is carried out to determine a fire classification level of A1, A2, B, C, D, E or F for insulation products intended to be used in wall and ceiling constructions. After treatment, EcoChoice timber achieved Euroclass B.

The TDCA recommends

The TDCA recommends only using fire retardant products that are applied in a controlled, factory process. If a fire-retardant-treated timber is to be used, there are required stipulations:

• The treatment must be approved by the WPA (Flame Retardants | The Wood Protection Association), 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 fire retardant is compatible with any subsequent products that are to be used e.g. coatings.

What about timber cladding in buildings under 18m?

For timber cladding and/or balconies on buildings where the upper floor level is less than 18m above ground, it’s still important to have an independent, professional fire risk assessment. This will assess the individual elements of the project and consider all building design, its use, the materials and its location.

You might find that an assessment like this determines that a flame-retardant treatment is unnecessary. However, in line with the Confederation of Timber Industries it is suggested that unless shown not to be necessary by an appropriate risk assessment process, all such timber-based cladding and balcony components should still be treated using quality assured factory-applied flame retardant to Euroclass B.

The important overarching point is that it’s best to err on the side of caution. Always seek professional guidance to determine whether your timber cladding should be treated with a suitable fire-retardant.

If you would like to find out more about our cladding options, please get in touch. Call us on 0345 638 1340, or drop us an email at sales@ecochoice.co.uk

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