What is the best timber to use for decking?

Things to consider when buying decking material

Durability

Different timbers have varying levels of natural durability and we are often faced with the question, “which is the best wood that does not rot?”  The timber species whether softwood, hardwood or modified timbers does not always indicate whether a type of timber is suitable for use as decking.   The Timber Decking and Cladding Association recommends that the choice of deckboard should have a minimum service life of 15 years, and should be rated as moderately durable (durability class 3) at least for above ground use and durable (durability class 2) for ground contact use.

 

*From EN 350:2016. Durability Class is quoted for heartwood only, the sapwood of any species is susceptible to decay unless treated or modified to protect against biological attack.

**From AS 5604-2005

Appearance

Timber decking designs not only depend on the shape and size of your deck but also the aesthetics. Softwood decking is usually treated with a high pressure preservative that gives the wood a green hue before weathering over time to a grey.

Hardwood decking offers a range of rich, natural colours from golden, light brown up to rich mahogany.

Accoya® decking is a pale, light straw colour but can be easily stained to create the finish you desire.  Due to the improved stability of Accoya® wood, coatings can last up to two times longer.

Accoya® wood decking in Italy

Accoya® wood decking in Italy

 

Installation and Maintenance

Softwood decking is easy to install. It is recommend to always fix with screws to allow for easy replacement of boards, and it is essential that any cut ends are treated with an end-grain preservative to avoid rot and decay.   Maximising the service life of a softwood deck requires more maintenance than other wood types with regular cleaning, and reapplication of preservatives.

Before installing hardwood decking, consider allowing boards to acclimatise as moisture content can vary. Boards can shrink and swell, therefore a gap of approx. 5mm should be left between boards (or roughly the size of a pencil!).  Hardwood decking timbers can be very dense and it is recommended to pre-drill boards before fitting screws.  It will take longer to install than a softwood deck, and a robust power tool is recommended.

As Accoya® wood decking is slightly acidic, like most durable woods, it is recommended to use A2 (general applications) or A4 (for seacoast exposures) stainless steel. To ensure a durable and lasting fixation, the boards should be fixed with at least 50 mm clearance to the end of the board (use self-drilling screws or pre drill the hole to 1 mm less than the shank diameter). Due to its dimensional stability, Accoya® deckboards will not shrink and swell and cause damage around fixings, or splinter so it can be classed as barefoot friendly.

Thermal Gain

A commonly asked question with regards to decking is, how hot will it get in warm climates?

Thermal gain on decks and terraces is a particular issue in the summer season. When designing your deck, particularly around pool areas, it is important that the deckboard is bare foot friendly.

A thermogram image analysis was arranged in Japan with the Hiroshima Prefectural Technology Research Institute to asses differences between Accoya®, thermally modified wood and three variants of commercial WPC decking.

The ambient temperature during the temperature of all decks was 32°C. Deckboard dimensions were comparable for all three types:

  • Accoya® 26 x 140
  • Thermally Modified Wood 26 x 140
  • WPC 25 x 145

The thermograms clearly indicate thermal gain in Accoya® is substantial less than the alternatives tested.

Sustainability

Choosing wood for your decking material is a more sustainable option than wood plastic composite.

Why is wood sustainable? 

Forests act as an important carbon sink by absorbing CO2 in the biomass of the tree and the resulting wood products. For maximum CO2 sequestration it is actually advised to harvest  sustainably managed forests / plantations for the production of  durable products.  The longer the lifespan of these products, the longer they can act as additional carbon stores while providing the forest the opportunity to regenerate and produce new biomass (acting as new carbon sink).

Supplies of certified tropical hardwoods are limited, resulting in illegal logging which, in turn, leads to the rainforest deforestation. In contrast, Accoya® uses a fast growing temperate, softwood species, Radiata Pine, from sustainably managed forests (FSC® certified), and due to the high yield and long life span is more efficient at locking away CO2 for longer. It is important to look for timber decking that carries the approval of a certification body such as PEFC® or FSC®.

Greenhouse Gas Emissions (kg CO2 eq per m3 of material) 

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