Wooden decks are an ideal way to blur the boundary the interior and exterior areas of a building. Steve Young, Timber Decking Association operations director, takes a look at choosing and using wood for outdoors use.
OVER THE PAST few years, something of a revolution has occurred in Britain’s gardens and commercial landscapes, we’ve rediscovered wood. The timber deck, an essential feature of everyday life in other parts of the world, has finally taken off here too. Wood that will last almost indefinitely outdoors is widely available here in the UK. No small wonder that wood is now seen as a viable proposition for permanent outdoor surfaces.
Wood is a very good looking material, and it has many practical benefits for outdoor use. A timber deck or walkway often needs only minimal foundation work and is quick to build compared to traditional patios and terraces. It is a great way to make-over unsightly concreted areas, an old paved patio or deal with uneven areas of an outdoor area.
Decks are ideal structures for sloping sites or in boggy ground or water, which creates a greater usable space without the need for major earthworks and retaining walls. The lightness of wood also makes it perfect for roof gardens.
One big benefit of the timber deck is that unlike a patio or terrace it can be built to the same level as the floors inside a property, creating the true outdoor room feel. Being a natural product, timber is pleasant to walk on, warm to the skin and can be designed to blend with any style of property and domestic or commercial environment.
Timber comes in two broad groups softwoods and hardwoods. Within each group there are many different species. Some are suitable for decking and some are not. Durability is the key requirement for all wood exposed to the elements. Wood will start to rot when its moisture content is persistently above 22% and oxygen is present. When specifying timber for outdoor applications, go for either a naturally durable hardwood or a softwood that has been made highly durable through an industrial wood protection process. These processes control the exact amount of preservative required by a particular component.
Posts and joists in contact with the ground or water need more protection than components used out of ground. Only use wood treated in line with BSEN 335 Use Class 4 for in ground and freshwater contact. Components treated to nothing less than Use Class 3 levels should be used for all out of ground applications.
Pressure-treated softwoods like European Redwood, Scots Pine and Southern Pines account for around 80% of all UK decks because they are less costly and easier to work with than hardwoods.
However, the rich colours, grain pattern and hardwearing qualities of suitable hardwoods add greatly to their appeal, particularly where commercial and high use leisure applications are involved. Currently, the most popular species are Ipé, Tatajuba, Balau, Iroko, Massaranduba and Oak. Properly constructed and maintained, hardwood or pressure-treated softwood decks will have a useful life expectancy of 20 years and more. This performance is reflected in the long-term warranties that are offered by leading suppliers of decking components.
Always make sure that timber for outdoor use is fit for the job and use corrosion resistant fixings that will last as long as the timber. Look for the Deckmark quality assurance symbol that means the manufacturer has been independently assessed by the Timber Decking Association (TDA) and operates the highest quality standards. Only use timber that whose source can be verified under supply chain schemes.
Deck boards come in a range of surface styles; plain, ribbed, grooved and hi-grip when additional underfoot security is required like on ramps, steps or door access points. At the time of installation all wood for outdoor use should have a moisture content no greater than 20%. This reduces the risk of distortion caused when timber with higher moisture levels dry to match the local conditions. Your timber supplier should verify this for you.
A good tip with deck boards is to open packs and lay the boards out for a few days, turning them occasionally, so that they adjust to your site before being permanently fixed in position. A gap of no less than 5mm and no more than 10mm should be left between boards to allow for the natural movement of timber over the seasons and help surface drainage and ventilation of the entire structure.
To aid drainage a slight fall of 1 in 100 should be built into the deck structure. If the deck is attached to a building then the fall should be away from the property. Grooved boards are designed to improve drainage and it therefore makes sense to position such boards with the grooves in the direction of the fall.
Surface deposits, together with mildew and algae, can cause any surface in the garden to be slippery in the wet. Building a fall into the deck to prevent standing water and routine brushing and a surface treatment every 24 months or so should help prevent the conditions that cause slipperiness.
For absolute underfoot security use high grip boards on ramps steps or in doorways. These boards come with a factory-fitted strip of an anti-slip resin or material and the best ones will have been slip resistance tested in line with BS 7976. A wide range of surface cleaners and treatments are available for application by brush or spray and the ICI Cuprinol range of Deckmark products includes an anti-slip coating.
While a ground level deck is a potential DIY project, raised, high level, cantilevered structures and roof decks are not. Specialist knowledge is required to ensure the deck is structurally safe and fit for the loads that will be placed on it. This involves selecting the correct structural grades and sizes of timber and verifying spans and load bearing capacities of beams, joists and balustrades.
It is essential that such structures are designed and built by experienced contractors operating to good industry practices. To reinforce this, the UK’s leading insurer of new homes, the National House-Building Council, now require that timber decks and landscaping on new properties comply with the guidelines of the TDA.