All mature trees have an inner core known as HEARTWOOD surrounded by an outer layer of younger SAPWOOD. The sapwood is where the tree stores the nutrients essential to growth. These food reserves remain after the tree is logged and sawn into components.
The heartwood of some species contains naturally occurring chemicals that make it relatively durable – the ability to resist decay and insect attack. The degree of natural durability varies from species to species.
Sapwood on the other hand is a source of food for many species of fungi and insects and is always vulnerable to attack. The risk of an attack increases significantly if, for any reason, the moisture content of wood rises above 20% – for example, poor installation practice or maintenance, persistent condensation, or damp.
Some degree of sapwood is likely to be present in the timber we use for building, hence the precaution is taken to treat certain timbers with preservative prior to use.
Wood protection technology helps to optimise the amount of harvested timber that can be usefully gained from the tree. Timber preservatives for softwood materials provide tailored levels of protection from decay and insect attack – making the resulting wood more durable and offering reliable longer-term performance.
Making the most of timber resources in this way also reduces waste and reduces pressure on the more naturally-durable, but perhaps more scarce species.
The preservative industry is highly regulated and manufacturers continue to introduce innovative products that are better targeted towards the organisms we wish to control and more environmentally benign.
Wood protection formulations tend to chemically bind into the timber after impregnation and are not free to readily escape in service.
At the end of its service life, treated wood can be re-used or recycled for approved applications or disposed of in a way that minimises any potential for environmental damage.
The benefits gained by using treated timber can be balanced against any relatively low negative impacts, especially when looking at the bigger picture – see Building with Wood.