Think you know everything about wood plastic composite decking?

The Timber Decking & Cladding Association takes a closer look at wood plastic (polymer) composite as an alternative to natural timber decking

Wood plastic/polymer composite (WPC) boards are manufactured using a mixture of wood fibre, plastic and other additives (eg, colourants, UV stabilisers). These are finely ground, mixed and made molten then extruded through an aperture plate to produce desired sizes and profiles – usually to mimic a timber texture. 

They are manufactured to individual formulas with varying percentages of timber content. This means the quality will differ from product to product. The use of waste wood and recycled plastic allows manufacturers to claim environmental attributes – but some use virgin plastic or polymers for all or part of this process. 

Some consumers will buy this product because of its environmental claims, so as a seller, it’s important to know about any available product information offered from the manufacturer. 

Additionally, it’s important to realise that only a handful of manufacturers currently offer to take back the products at their end of life, so recycling the product – which contains plastic – may prove problematic.

Deck design options 

SmartBOARD composite decking from Stamco Hoppings.

WPC deck boards are usually available in a choice of colours and textures, and either hollow or solid, capped or uncapped, grooved or smooth profiled, and single or dual-sided.

All these factors can have a bearing on the performance and/or the cost of the wpc product. For example:

  • Hollow boards offer a more economical and less heavy option to solid boards.
  • Capped boards have a wholly plastic layer of protection against scuffs and stains.

Hollow boards are unlikely to be as structurally strong or stable as solid boards, while uncapped boards may not offer sufficient protection from staining and wear and tear. Colours may fade and/or need maintaining depending on the product, deck location and use. As a seller, always ask your customer about the deck’s intended use and know about any performance data offered from the manufacturer.


Relatively heavy WPC is generally not as strong as timber, so it’s likely that deck substructure joists will need spacing closer together to provide adequate support. WPC boards tend to expand along their length as opposed to timber, which expands width-wise. So appropriate expansion gaps are usually required between abutting deck boards and adjacent surfaces. Specialist fixings are used with WPC products – these include ‘secret’ fastener clips and colour-matched trim fixings.

Many manufacturers offer performance warranties – valid only if the product is installed to their exact instructions. Again, it’s important to share this installation advice with your customer. You could also supply the appropriate fixings to complete the sale.


WPC products will, over time, change in appearance due to weathering – the rate of change being quality dependent. Some WPC brands may recommend the use of special cleaning or reviving products. In terms of decking, it’s important to note that ALL outdoor flat flooring surfaces require basic cleaning routines. This is to avoid the build-up of debris, algae and moss – key culprits of deck slipperiness.

Always refer customers to the WPC manufacturer’s recommendations on cleaning, so as not to invalidate any service life or colour warranties.

Slip-resistance properties

Many WPC decking board products claim anti-slip properties (without the addition of any anti-slip aggregate material). The Health and Safety Executive (HSE) states that flooring is considered to have a low slip potential if it achieves a pendulum test value (PTV) of at least 36. In terms of outdoor decking, this is more appropriate if a wet deck test surface achieves this score, not a dry one.

The TDCA recommends routine slip testing for public access decks – regardless of the deck material. To find a tester, or for further guidance on slip resistance, visit the UK Slip Resistance Group online at

Quality approved

Many TDCA members supply wooden deck components, independently verified under our DeckMark quality product scheme. Several supply or manufacture WPC products too – yet independently accredited products are rare. If you supply such products, are confident of their quality and want them to stand above the rest, why not work with the manufacturer to
gain DeckMark approval? Contact for more information.

If you have questions on timber decking and cladding, from planning regulations to installation advice, visit the TDCA website where you’ll find FAQs, free downloads and an Approved Supplier search.