TDUK SupplyingTimber Issue 8 DIGITAL - Magazine - Page 56
———— TIMBER DECKING ————
ENSURING SAFE DECKING: THE
How to make sure the deck boards, joists and substructure products
you sell, buy and install are safe and 昀椀t for purpose.
M
USING TIMBER
USING
TIMBER
exterior structural supports.
This classi昀椀cation clearly
places decking substructure
components within the Use
Class 4 category.
TDCA Director Janet
Sycamore explains: "The Use
Class system is essential
because it indicates the scale
of the biological risk a wood
product faces in a speci昀椀c
environment and determines
the required preservative
loading and penetration of
wood preservative to achieve
the desired service life."
Don't take risks with
safety critical products
Since external use presents a
higher biological risk to wood,
and structural supports are
safety critical, it is alarming
that the TDCA has observed
widespread use of Use Class
2 internal 昀氀oor joists in deck
substructures. These joists are
unsuitable for outdoor decking
and should only be used
SUPPLYING TIMBER
56
inside buildings. The default
desired service life for correctly
treated and installed Use Class
4 joists is 15 years (30-year
speci昀椀cation is also possible);
but this would be severely
compromised were UC2 joists to
be used.
To improve standards and
promote the safe use of timber
in deck construction, a wider
network of correctly treated
UC4 deck joists is needed,
along with better point-of-sale
and online information.
Janet continues: “It is
challenging for purchasers
to navigate the appropriate
standards. We are seeing
widespread use of UC2
internal 昀氀oor joists in deck
substructures, leading to
inevitable underperformance.
"This short-sighted approach
not only undermines consumer
trust but also threatens the
long-term viability of the timber
decking industry. Through our
educational and promotional
SPRING 2025
↗
any timber
decks in the
UK could be
unsafe due
to inadequate speci昀椀cations
and/or poor installation
practices, according to the
Timber Decking and Cladding
Association (TDCA).
Many of these issues stem
from the poor availability of
correctly treated, strengthgraded structural substructure
timber and the use of
inappropriate metal 昀椀xings
– the latter is a subject for
another time.
Pressure-treated softwood
is commonly used to build
the decking substructures
that support timber and
composite deck boards. Correct
preservative treatment provides
softwood with the added
durability necessary to allow
successful outdoor use.
However, it’s a mistake to
assume that all pressuretreated wood is the same. While
one piece of treated wood
may look very much like any
other, the level of preservative
protection could be very
di昀昀erent. That’s because BS
8417 requires that the loading
and penetration of preservative
impregnated into the wood is
tailored to the desired end use.
End uses are categorised
into 昀椀ve categories. Use Class
3 applies to exterior above
ground use such as deck
boards, whereas Use Class
4 covers exterior groundcontact use applications and
Image ©
TDCA. Timber
decks are
safety critical
and it's vital
that the right
substructure
timber is used.
