Maintenance ensures protection remains functional Durability- Natural Durability Biological/ Physical Hazards TIMBER Species Natural durability of heartwood Weathering Fire Chemical Design Detailing minimises exposure to hazards Treatment enhances durability of sapwood Fungi Termites / borers Marine
Natural Durability • Measure of resistance of heartwood (older wood) to fungal or insect attack • Used when selecting a species for a specific function • Can match the hazard with natural durability and avoid the use of treated timber • If can’t find readily available timber with appropriate ND, use a treated timber product • Measured by field trials in which small samples are driven into the ground at different sites around Australia. Regularly inspected for signs of decay or attack
Natural Durability • Different for different species • Different natural chemicals (extractives) stored in wood as a by-product of growth. • Some extractives are toxic to fungi and insects • Different cell structures in different species allow some insects to breed in the cells. Other species will not accommodate their eggs • Find ND for Australian species in AS5604:2003 (also in AS1720.2.)
Natural Durability (Sapwood) All sapwood has low natural durability • Starches transported in the sap are very attractive to all fungi and most insects.
Natural Durability (Heartwood) Extractives and growth characteristics affect natural durability of timber species Tallowood Blackbutt Sydney blue gum Tasmanian Oak
Long-term Performance of Timber Can match natural durability class with environmental hazard to estimate long-term performance of untreated timber heartwood