Stepping up decking standards

Janet Sycamore outlines forthcoming changes for suppliers and manufacturers.

Decking substructure is equally as important as the deck board. Photo: Hoppings Softwoods Plc

“The substructure (posts, beams and joists) is equally as important as it forms the ‘system’ that supports the whole deck construction.”

The popularity of decking soared last year when circumstances forced people to spend more time at home and outdoor living became increasingly important. The Sunday Times confirmed that ‘Britain has fallen back in love with decking’.1 Readers were told: ‘If you choose timber, look for boards with the DeckMark symbol from the Timber Decking and Cladding Association.’ The article also recommended the Timber Decking and Cladding Association (TDCA) database for finding suitable installers – it is a mandatory condition of TDCA membership that installers are accredited to DeckMark standards, ensuring they are of high calibre and experienced in their craft.

The article focused on wood polymer composite (WPC) deck boards. Whatever material you choose for your decking, it is important to ensure quality verified products are used throughout and manufacturers’ guidelines are adhered to.

A decking project consists of several components – going from the ground up; posts support the beams, beams support the joists and joists support the deck boards. Every part of this structure is reliant on the other, but all too often the focus of attention is predominantly on the deck board as it is the most visible part of the deck. The substructure (posts, beams and joists) is equally as important as it forms the ‘system’ that supports the whole deck construction.

Whatever deck board you choose, in most cases the substructure will be made from preservative pressure-treated timber. The question is, will it be fit for purpose by being treated to the correct specification according to BS 8417 (the standard for wood preservatives in the UK)?2

Deck joist specifications: prepare for change

It is the role of the TDCA to provide relevant information to ensure decks are installed correctly, to give a long service life. This includes promoting sources of quality materials and services that carry independent accreditation.

The TDCA has had to prepare the industry for a change in standards with regards to specification for decks. Going forward, all decking substructure components – not just posts, will be regarded as Use Class 4 application (outdoor, in ground contact) where previously they were Use Class 3 (outdoor, above the ground). The TDCA supports this >>

positive move as it ensures timber used on or very close to the ground (as a lot of decks are set), will be treated to a higher standard. It brings us into line with Sweden, Finland, France and North America, where decks are regarded as safety critical end-use applications.

The specification for deck joists will change when BS 8417 is next updated, but the TDCA is urging its members to be prepared and make necessary adjustments now as the changes provide a more robust approach.

Research highlights knowledge gaps

Research sponsored by the Wood Protection Association (WPA) has revealed a severe lack of understanding about preservative-treated timber among front-line merchant sales staff and end-users. The well-researched customer A completed deck. Photo: Deckbuilders (UK) Ltd

or specifier might know what they want, but will they find it on the shelf, will it be correctly labelled by a timber outlet note) verification of treatment Use Class, desired service life and will they obtain sound advice to ensure they purchase the and compliance with BS 8417. Water shedding details, such correct materials? The WPA research would suggest not. as scarfing or sloping horizontal surfaces to aid water run-off, are also important.

It is a mistake to assume that all pressure-treated wood is the same. One piece of treated wood may look much like another, but the level of preservative protection could be different. A deck board is a distinctive identifiable component, but joists and beams are more problematic as they can be confused with roofing joists, which are wholly inappropriate for exterior use. The buyer needs to clearly state that the joists are for external use and must be treated to a ground contact specification – Use Class 4. The supplier must confirm in writing (on the invoice or delivery TDCA, WPA and the Timber Trade Federation are now working collaboratively to address this knowledge gap for the greater good of the timber industry. The joint campaign, which uses the ‘Make sure it’s 4’ device and a ‘Use Class 2, 3 or 4’ theme, commenced last year and is regarded as a long-term commitment (see article on p141).

Wood polymer composite standards

As illustrated in The Sunday Times article, the UK decking market has a wider acceptance of composite (WPC) deck boards driven by the promise of environmental credibility, enhanced durability and ease of maintenance. WPC is a relative newcomer and its performance attributes are less well understood. Following an increase in the number of issues

Composite timber Alchemy decking. Photo: BSW Timber

being reported to the TDCA, it became apparent that not all products are fit for purpose. This resulted in the TDCA working with the industry to develop a Product Approval Scheme (PAS) for wood-fibre based, wood polymer deck boards.

A scheme document, based on current European standards, sets out what is needed to achieve accreditation. It features nine testing requirements that sets pass and fail criteria. The requirements include physical and mechanical properties, biological and physical durability, fire performance and slip resistance.

The scheme also requires that clear, unambiguous information is given to the buyer in terms of guarantees, recycled content and any infrastructure in place to facilitate recycling. The rationale is to create more order and transparency to the market. The scheme will actively endorse good-quality composite deck boards allowing endusers to review product credentials prior to purchase.

The funds generated from membership of the scheme will be used to develop further resources to help promote goodquality decking and cladding products and installation practices. n

About the author

Janet Sycamore Head of Operations Timber Cladding and Decking Association

Further information

The Timber Decking and Cladding Association is a not-for-profit, technical and advisory body that exists to help professionals and consumers make the most of wood. It operates DeckMark, a quality scheme for products and for design and build contractors, and has a mission to develop the awareness of and demand for quality timber decks, associated landscape structures and external timber cladding – hand in hand with the best practice workmanship required to produce such projects. Raising awareness about the consequences of cutting corners and educating buyers about the properties of quality decking materials, design and aftercare are core activities.

Further reading

Timber decking: The professionals’ manual, 3rd edition, ISBN 978-1-909594-75-3, BM TRADA, 2018

References

1. The Sunday Times, 28 June 2020 2. BS 8417:2011+A1:2014 Preservation of wood. Code of practice, BSI