It’s a well-known fact that timber expands and shrinks based on the relative humidity of the environment. All timber species absorb moisture from the air. Rising humidity levels will cause the timber to absorb more moisture and expand. Conversely, shrinkage will happen when relative humidity in the surrounding air decreases, causing the timber to lose moisture.

Timber movement – both expansion and shrinkage – must be accounted for when specifying wood for architectural use, especially on facades. Expression cladding from Woodform Architectural applies research-based design to calculate shrinkage and expansion in timber cladding after factoring in project-specific considerations.

Why choose low-shrinkage timber

A high-quality surface finish can slow down the rate of moisture exchange in timber cladding, but not indefinitely. Weather conditions in Australia tend to swing wildly, from hot to cold, then wet to dry. The choice of timber species also influences timber movement, and there is a complex formula used to calculate and accurately predict such movement.

When selecting timber cladding systems for the facade, it is important to provide allowance for timber movement as well as choose low-shrinkage timber.

Woodform Architectural presents two readily available timber species that stand out for their low moisture movement qualities.

Burnt Ash

A thermally modified White Ash variety, Burnt Ash changes from a pale hardwood into a rich medium-to-dark chocolate colour through thermal modification. Burnt Ash experiences a very low average tangential shrinkage (in the direction parallel to the growth rings) of 0.5 per cent, in part due to the chemical-free, high-heat process.

Pacific Teak

A sustainably sourced hardwood variety native to Papua New Guinea and the Solomon Islands, Pacific Teak has a pale yellowish to creamy olive appearance. Similar to Burnt Ash, it also has a very low tangential shrinkage average (2%), making this durable timber species with lustrous texture ideal for exterior cladding.

Image: Burnt Ash