Durability class
Durability class (DC1-DC4): AS 5604 rating for timber's natural resistance to decay and insect attack. DC1 is very durable (e.g. merbau); DC4 is slightly durable.
Ask Chalkline about this →Durability class
Durability class (DC) is the rating assigned to the heartwood of a timber species under AS 5604:2022 to indicate its natural resistance to fungal decay and insect attack. Classes run from DC1 (very durable, 25+ years in-ground) down to DC4 (slightly durable, short service life without treatment).
Durability class applies to the heartwood only, not sapwood. Common decking species: merbau is DC1 above-ground; spotted gum and ironbark are also DC1 above-ground. Treated pine does not have a natural durability class; its service life is determined by the hazard level (H3, H4) of the preservative treatment applied.
Where timber must contact the ground or remain continuously damp, DC1 heartwood or H4/H5 preservative treatment is required.
Also known as: DC1, DC2, DC3, DC4, natural durability rating
Category: Timber specification
Related
See also
Last updated: 2026-05-08. Verified: 2026-05-08.