Understanding the Jargon and Protecting the Supply Chain

Timber often receives a negative press from the wider building industry due to its perceived limitations when it comes to its reaction to fire – using the correct Fire Retardant (FR) treatment makes an enormous difference.

With the correct treatment, timber has excellent FR properties and its reaction to fire is extremely low. Industry regulations are in place to protect people’s safety, health and welfare. However, sometimes it can be confusing. Reaction to fire is how the material will allow a fire to spread and is a consideration in buildings where evacuation time is critical, and Resistance to fire is how the material will perform when on fire, i.e. how long will it retain its structural integrity. This is particularly important for floors and ceilings where the material may lose its integrity causing it to collapse.

Below is a quick guide to help explain the jargon.

• FR treated solid wood (timber cladding) and plywood must be supplied with a CE mark as a legal requirement under the Construction Products Regulation (CPR) EU no. 305/2011

• The relevant harmonised standards are BS EN 14915:2013 (solid wood) and BS EN 13986:2004 (plywood).

• If a product has a CE mark, it means that the method in which it has been produced and the properties of the product meet certain criteria as defined in the harmonised standards.

As with the above standards, there are stringent processes that must be followed when treating timber. The manufacturer or person significantly altering the product (this would be a timber treater in the case of FR treatment) must have a clearly defined manufacturing process. This process must be audited by a notified body which will initially grant certification. They will also be responsible for ongoing surveillance to ensure the accreditation is maintained.

The FR chemical manufacturer will provide the treater with a fire classification report, by species, which is issued and audited by a notified body under Assessment and Verification of Constancy of Performance (AVCP) system 1. The notified body can then audit the treater under AVCP system 1 against the FR classification report. They can then grant the FR treater with a CE certification for their process. This comes in the form of a Certificate of Consistency of Performance (CoCOP) and allows the treater to issue their customers with a Declaration of Performance (DOP) with each supplied batch of treated timber. The DOP ensures full traceability of the FR treated timber when it enters the supply chain. AVCP is a harmonised system defining how to assess products and control the constancy of the assessment results. This system safeguards the reliability and accuracy of the DOP.

DOP’s are species specific. Different species have different cell structures and/or densities which can have a significant effect on the quantity of chemical required during pressure impregnation. As a result, the FR treatment process varies depending on the species in terms of treatment time and pressure. It is therefore essential that the species details are provided by the treater’s customer and the treater has the appropriate DOP to allow them to treat the specific species in question.

Understanding COP and DOP Documents

Typical COP and DOP will contain the following information:

• Product: details of the timber species – e.g. Larch: what it is, e.g. solid wood panel, tongue and groove profiled; and what fire retardant treatment has been used e.g. Burnblock. Classification is valid for the end use as cladding or as support for cladding elements

• Thickness: what is the nominal thickness of the material i.e. 21,5mm • Density: what is the timbers nominal density range i.e. 650 - 750 kg/ m3

• Intake: how much dry FR material must be absorbed in line with the approved factory control process. Dry amount of FR 36.5 kg/m3

• Substrate: details of the substrate that must be used to mount the timber onto any substrates in classes A1 and A2-s1, d0 of at least 9 mm thickness and with a density equal to or greater than 653kg/m3

• Fixation: how cladding should be fastened, e.g. mechanically fixed to the substrate

• Air gap details of whether an air gap (typically 40mm) behind the panel is required

• Mounting: how panels can be mounted, e.g. horizontally, vertically or both

• Joints: how panels can be joined e.g. vertical, horizontal joints or both

• Reaction: reaction to fire classification: what rating has been provided for the above conditions, e.g. B-s1,d0.

FR treatment is also species specific. Generic terms such as Far Eastern plywood, softwood and hardwood are ambiguous and do not meet the requirements of an FR Classification Report and therefore not CE compliant.

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