FEATURE TIMBER TREATMENT
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.
W
ith the correct treatment, timber has excellent FR
DOP’s are species specific. Different species have different cell
properties and its reaction to fire is extremely low.
structures and/or densities which can have a significant effect on the
Industry regulations are in place to protect people’s
quantity of chemical required during pressure impregnation. As a result,
safety, health and welfare. However, sometimes it can
the FR treatment process varies depending on the species in terms of
be confusing. Reaction to fire is how the material will allow a fire
treatment time and pressure. It is therefore essential that the species
to spread and is a consideration in buildings where evacuation time
details are provided by the treater’s customer and the treater has the
is critical, and Resistance to fire is how the material will perform
appropriate DOP to allow them to treat the specific species in question.
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
Understanding COP and DOP Documents
lose its integrity causing it to collapse.
Typical COP and DOP will contain the following information:
Below is a quick guide to help explain the jargon. • •
• •
Product: details of the timber species – e.g. Larch: what it is, e.g.
FR treated solid wood (timber cladding) and plywood must
solid wood panel, tongue and groove profiled; and what fire
be supplied with a CE mark as a legal requirement under the
retardant treatment has been used e.g. Burnblock. Classification
Construction Products Regulation (CPR) EU no. 305/2011
is valid for the end use as cladding or as support for cladding
The relevant harmonised standards are BS EN 14915:2013 (solid
elements
wood) and BS EN 13986:2004 (plywood).
•
Thickness: what is the nominal thickness of the material i.e. 21,5mm
If a product has a CE mark, it means that the method in which it
•
Density: what is the timbers nominal density range i.e. 650 - 750 kg/
has been produced and the properties of the product meet certain criteria as defined in the harmonised standards.
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
As with the above standards, there are stringent processes that
•
must be followed when treating timber. The manufacturer or person
timber onto any substrates in classes A1 and A2-s1, d0 of at least 9
significantly altering the product (this would be a timber treater in the case of FR treatment) must have a clearly defined manufacturing
mm thickness and with a density equal to or greater than 653kg/m3 •
process. This process must be audited by a notified body which will initially grant certification. They will also be responsible for ongoing
Substrate: details of the substrate that must be used to mount the
Fixation: how cladding should be fastened, e.g. mechanically fixed to the substrate
•
surveillance to ensure the accreditation is maintained.
Air gap details of whether an air gap (typically 40mm) behind the panel is required
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
or both •
Performance (AVCP) system 1. The notified body can then audit the treater under AVCP system 1 against the FR classification report. They
Mounting: how panels can be mounted, e.g. horizontally, vertically Joints: how panels can be joined e.g. vertical, horizontal joints or both
•
can then grant the FR treater with a CE certification for their process.
Reaction: reaction to fire classification: what rating has been provided for the above conditions, e.g. B-s1,d0.
This comes in the form of a Certificate of Consistency of Performance (CoCOP) and allows the treater to issue their customers with a
FR treatment is also species specific. Generic terms such as Far
Declaration of Performance (DOP) with each supplied batch of treated
Eastern plywood, softwood and hardwood are ambiguous and do not
timber. The DOP ensures full traceability of the FR treated timber when
meet the requirements of an FR Classification Report and therefore not
it enters the supply chain. AVCP is a harmonised system defining how
CE compliant.
to assess products and control the constancy of the assessment results. More at www.wj-group.co.uk www.trada.co.uk
This system safeguards the reliability and accuracy of the DOP.
Timber Trader UK Magazine
Spring 2021
30
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