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Not just a timber deck

Mike O’Brien, Technical author, treads the (deck) boards.

The recent ban on smoking in pubs is likely to cause the owners of pubs, clubs, restaurants and hotels to construct outdoor spaces for smokers to gather. The growth in the construction of timber decks is likely to accelerate to meet this need. Standards set by the Timber Decking Association and the Timber Research and Development Association make the specification of a timber deck a clear and structured process.

However, timber is not the only material to consider when constructing a deck. Timber structures have limitations and in some situations, such as cantilevered or heavily-used decks with vehicular access, a steel structure with timber deck boards may be more appropriate. The connections between the boards and the structure may require pre-drilled fixing holes or an adjustable slotted fixing system, so accurate detailing will be essential. The photo (by Mike O’Brien) shows FSC-certified timber boards fixed to a steel channel system on a galvanized steel frame, cantilevered over the river Ouse in York.

Recycled plastics

Several examples of recycled plastics boardwalks have been installed in recent years. The materials available contain up to 100% recycled content, sourced from plastic bags, bottles and gas and water pipes. They are particularly suited to constantly wet locations, where timber rot and leaching would be recurring maintenance problems. Some case studies are available on the Waste and Resources Action Programme (WRAP) website, www.wrap.org.uk, where a whole life costing exercise indicates that, over a 40-year life span, the total cost of a timber boardwalk will be more than twice the price of a comparable recycled plastics boardwalk.

Some disadvantages of recycled plastics boards include high initial capital costs, limited availability, limited colour range (black or brown), weight (heavier than softwood boards) and high flexibility, particularly in warm weather, which requires a closer joist spacing than for equivalent timber sections. Advantages include high durability without the need for preservatives, no knots, splintering, checking or warping, strength retention over long periods in use, easy working with normal tools, and slip resistance.

Wood polymer composites

Wood polymer composite (WPC) materials have been available in the USA since the early 1990s and have recently entered the UK market. They are manufactured from a combination of waste wood dust and recycled plastics, providing the durability of plastics with the low thermal movement of timber. The resulting product is over 95% recycled material. WPC boards are available in a wide variety of colours and applied textures (e.g. faux timber grain) and can take a stain or painted finish. Initial cost is higher than either recycled plastics or timber, but products generally come with a 25 year guarantee and can be used in locations where aesthetics may preclude the rugged appearance of recycled plastics boards.

PVC-U

PVC-U is a material that some designers might avoid, for a variety of reasons. However, the durability of PVC-U has improved and the material is increasingly being used in exterior applications, from cladding to furniture, fences and now deck boards.

PVC-U deck boards are not solid – they are extrusions that clip on an underlying galvanized steel subframe or may be attached to a traditional timber structure. The board is textured to provide a slip resistant surface that doesn’t need to be re-applied or replaced as it ages. The boards are very durable and are maintenance free, and if a section is ever damaged, it can easily be replaced. PVC-U may be suitable in locations where environmental conditions are very severe or where access for maintenance is not easily achieved. Increasing use of PVC-U products may also encourage further developments in recycling technologies.

In conclusion, the most common material used in deck construction will always be timber, but don’t let this fact limit your choice.

	Hardwood	Softwood	Recycled plastics	Wood polymer composites	PVC-U
Recycled content			••	••
Low embodied energy	•	••
No preservatives required	•		••	••	••
No knots, splintering or warping			•	•	•
Naturally slip resistant			•	•	•
Paints and stains easily applied	•	•		•
High durability/ low maintenance	•		••	••	••
Low thermal expansion and contraction	••	•		•	•
Natural appearance	••	••		•
Low capital cost		•
Low lifetime cost			•	•	•
Readily available	•	••

Confirmed as current July 2007

 

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