Whilst hardwood is generally the preferred lumber species for exterior decking due to its hardness, resistance to wear and attractive colour, softwood species are commonly used, particularly where cost is an important factor. But the drawback of most softwoods is that they are not naturally durable so are unsuitable for use in areas fully exposed to the weather unless the wood is properly treated with a recognized wood preservative or completely sealed with an impervious surface coating. So when selecting a softwood species, one of the most important considerations is that these species used should be either a recognised naturally durable species such as Western Red Cedar, some species of cypress, larch or pine, or that it has been treated with an appropriate and good quality preservative.

For more than 70 years, the most commonly accepted wood preservative treatment chemical has been CCA (copper chrome arsenic), which gained popularity due to its effectiveness and relatively low cost. (CCA treated lumber can normally be distinguished by the greenish tone it imparts to the wood). However in recent years, many national organisations and authorities have announced either bans or restrictions on the use of lumber treated with CCA. For example, in Australia from March 2006, CCA treated timber will no longer be permitted for use as handrails, decking boards, picnic tables, or children's playground equipment in new installations. And in Japan, CCA treated lumber is generally not permitted any longer for public use in major cities for municipal projects.

Although there is apparently no firm scientific proof to support the contention that CCA timber is harmful to health provided it is handled correctly, such cautions or bans have been instituted as a precautionary measure. Nevertheless it is always best to err on the side of safety, so it is recommended that when working with CCA treated lumber, to apply protective clothing including goggles, face mask and gloves. CCA treated lumber also should never be burnt in an open fire but must be disposed of according to local regulations.

Fortunately a number of alternative wood treatment products to replace CCA are now available, the most common of which is probably ACQ (alkaline, copper, quaternary). Such products use low toxicity, active ingredients such as recycled copper and modern organic biocides to give the lumber the required long-term protection against wood destroying fungi, termites and other wood eating insects. Although such products have not been available for a sufficiently long time for extensive natural durability data to be collected, most manufacturers will provide at least 25 years guarantee on the life of treated lumber.

So if you wish to use a softwood species for your deck, check what preservative treatments have been applied, and especially with the newer preservative treatment chemicals, ask what guarantee the lumber supplier is prepared to offer on the lifetime of the decking material. Although untreated softwoods typically have a very short life in exterior exposed conditions, if pressure treated with appropriate chemical, a softwood deck will provide many years of continual use and enjoyment.

Malcolm Kay is the CEO of Intex Pacific Pty. Ltd. an international supplier of landscape materials including modular decking tiles. For more information see http://www.swiftdeck.com