Treated wood is a tried and tested foundation material when building a new house – and a valid option that delivers two added bonuses, according to New Zealand Timber Industry Federation deputy director Kevin Hing.
“Its green credentials are impeccable, and it is impossible to beat the warm, friendly feel of a building with timber foundations and a timber floor system.” In the past, timber foundations were also applied widely in structures such as bridges, as well as in multi-storey buildings.
The four-storey Old Government Buildings in Wellington, built in 1876 and today one of New Zealand’s historic landmarks, were constructed on totara piles, which were only changed to concrete when the building was renovated in the mid-1990s. Mr Hing says the New Zealand Building Code specifi es a minimum 50-year life for H5-treated pole foundation piles.
“The actual life expectancy of timber foundations is much longer. It’s true that a permanent wood foundation must be treated with the right mix of chemicals to ensure it never rots or is attacked by insects and remains maintenance free.
“In New Zealand, CCA – a mixture of copper, chrome and arsenic – is fixed into radiata piles. But the formula has been around for half a century. As recently as 2003 the Government reviewed CCA, and found it to be an effective and safe timber preservative,” he says.
The primary New Zealand Standard for timber construction, including timber foundations, is NZS 3604: Timber Framed Buildings. Additional relevant material is NZS 3602, which covers the use of timber in building, including grades and treatment of the various building components.
Mr Hing says considering the advantages and environmentally friendly characteristics of timber foundations, they could be used on a much larger scale in New Zealand.
“We believe it is a good building practice, delivering thermal efficiency, especially for a cold, wet climate.
“Timber foundations mean the floor is off the ground and air can circulate underneath, which renders the house less prone to damp, with the consequent health and comfort advantages. You get a nice, warm and attractive floor, which is softer on feet.
Houses built on timber foundations are higher off the ground, meaning they are also unaffected by surface flooding.
And very important – timber as a building material is sustainable. It’s a carbon store and a number of studies have proved it takes less energy to produce than other foundation materials. It’s the green option,” he says.
He lists other benefits to be:
New timber grading and design standards and requirements ensure there will be no issues with, for example, spring in the floor while, at the same time, the foundation is not a rigid platform and has high seismic resistance,
It compares well with other construction materials in terms of cost although, in some instances, such as sites with a slope up to around 10°, it might be more cost effective to use concrete rather than timber,
It has flexible design options – for example, getting a level floor with good indoor-outdoor flow to a deck area on a sloping site, and
It offers speed of construction. Mr Hing says another important advantage to the consumer is that timber is a generic product without branding, product differentiation or different systems.
“It keeps things simple and easy. If you buy from a reputable vendor, use timber treated to a quality assurance programme such as WOODmark and build to standard, you can always be sure of strong foundations that will comply with all the regulations,” he says.
