Architects Datafile (ADF) – Timber in Architecture (Supplement – August 2019)

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nowledge of fire protection
terminology in the design and
build sector is woefully low.
That’s according to a recent survey of
architects by the Wood Protection
Association (WPA). The findings of this
survey came as no surprise to the Timber
Decking and Cladding Association (TDCA),
which has long held the view that poor
specification of preservative and fire
protection treatments leads to compromised
timber performance.
The TDCA and WPA exist to support
architects and specifiers in their correct
choice of timber. This specialist knowledge
and expertise must be embraced throughout
the industry to ensure specifications are
always fit for purpose.

The extent of natural durability
How to correctly specify timber for
durability is a common question asked of
the TDCA. Some timbers (mainly
hardwoods) offer natural durability. They
can withstand outdoor and ground contact
for a determined service life without coating
or treatment.
BS EN 350: 2016 provides durability
classifications for different timber species.
There are five classes, Class 1 being the
most durable. A table detailing the expected
service life of different species for various
locations can be found in BS8417 (the
British standard for wood preservation).

When to specify preservative
treated timber
If you’re intending to use a softwood timber
outdoors, some level of factory preservative
treatment will most likely be necessary. For
outdoor use, timber is generally treated to
Use Class 3 or 4 dependant on application,
be it above or in ground contact.
A proven method for decades, pressure

treatment involves impregnating the

decking or cladding timber with a wood

preservative (most commonly, copper-

based). It’s a tightly controlled procedure

with checks for the level of treatment and

how far the preservative penetrates.

BS8417 details the specific requirements

for timber preservation.

Not only will the right specification of

treatment achieve the desired service life, it

will also lock up carbon for longer and

enable less durable timbers to be effectively

used for longer-term applications; an

environmental boon.

Modified woods are a more recent

innovation gathering pace. They employ

processes that physically alter the timber

Janet Sycamore of the Timber Decking and Cladding Association

discusses why and how the details of timber protection needs to be

embraced to ensure specifications are always fit for purpose

Is your timber specication

t for purpose?

VODAFONE BUILDING

Glenalmond Abodo cladding to the building in

Christchurch, New Zealand is made from thermally

modified softwood

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