What is Chemical Delignification & Is It a Structural Problem?

Chemical delignification is the breakdown of lignin, the natural glue that holds timber fibers together. Over time, this weakens the timber, causing it to collapse as fibers detach—often referred to as “hairy timber.”

Where Does It Occur & Is It Structural?

This issue commonly affects roof battens in the roof loft space, particularly during pre-purchase building inspections. While other roof timbers can be affected, battens are the most vulnerable due to their size and position. If a timber-framed roof with tiled covering suffers significant delignification, roof collapse is likely before structural framing is compromised.

Though delignification is more common in low-durability timbers like Douglas Fir (Oregon), even durable timbers like Jarrah (15–40-year durability rating) have been affected in Perth homes.

While it takes years to cause collapse, it is classified as a major defect in inspections. Walking on a roof with delignification is not recommended, as collapse may occur. The cause of delignification may also impact the health of occupants.

What Causes Chemical Delignification?

It occurs due to airborne chemical attacks on timber, including:

• Coastal exposure: Salt-laden air, worsened by terracotta tile fretting.

• Pollution: Proximity to industrial areas or main roads.

• Gas exposure: Leaks from slow combustion stoves, gas appliances, or hot water systems in the roof space.

Can It Be Prevented or Fixed?

Prevention is difficult due to environmental factors, but sealing roof battens with pale boiled linseed oil can extend their lifespan.

Important: AS 4349.1-2010 (Timber Pest Inspections) does not cover chemical delignification. If concerned, include a building inspection clause in your contract. At Cap-It-All Building Inspections, we inspect roof loft spaces (subject to access), ensuring you make informed decisions.