Composite Decking- Point’s to be aware of

I’ve just had a read of Aston dot’s Blog ( on composite decking also known as Wood Plastic Composite (WPC) Decking.

It’s a good discussion on the advantages of Composite Decking over traditional timber decking. I worked with Earth-wood and the lower maintenance costs, non- slip and the quality of finish made it an attractive proposition to customers.

Unfortunately Aston Dot is wrong on a number of points that he makes.

Composite decking for structural components

I’m afraid as yet I wouldn’t recommend Composite materials for structural components. While a lot of research was going into their use, it’s something you’ll need to be very sure about. The problem with WPC as used in decking is that they use Thermoplastic materials such as High Density Polyethylene (HDPE), Polypropylene (PP) or Polyvinyl Chloride (PVC). From recollection Ecodeck referenced in the article use HDPE. These materials are susceptible to a phenomena known as creep where they distort over time when exposed to pressure (either constant or occasional).

Hence if WPC is used for load bearing applications they are susceptible to warp and distort which could be potentially dangerous.

Composite decking is NOT dimensionally stable

While timber decking will expand when wet, and will shrink again during a dry summer. WPC decking is the opposite; it will expand in warm weather and shrink during the colder winter. We had a customer who ignored our installation guidelines and did not leave a 5 mm gap at the either end of plank. After a few warm weeks 2 planks butted up against each other and created a ridge in the deck.

Composite decking is NOT 100% environmentally friendly

I’m afraid nothing man made is, from the energy required to make the plastic in the first place, the energy required to recycle it and the energy and additive required to manufacture the WPC decking. I don’t know if it is more environmentally friendly than timber sustainably managed forests, but then the life span is significantly better than the softwood timbers from these forests.

Final word

Don’t get me wrong, WPC decking is a great product, we had a really good business supplying into marinas and public walkways as well as for domestic & commercial decks. It is long lasting, easier to maintain and keep clean, will not splinter from drying out. It will crack due to “Stress Crack Propagation” over time, especially if poorly installed but it’s better than timber for crack resistance and you know nothing is completely perfect.


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