In the past, this type of timber damage has been referred to using many different terms, Hairy Timber or Defibrosis.
In the early 1990's it was agreed that the true description of this type of timber deterioration is Chemical Delignification.
This term describes the deterioration in its true form, the lignin in timber is damaged by airborne chemicals.
Lignin is the natural glue that holds the fibres of wood together and is, therefore, a major component of any wood. When the lignin is broken down or damaged the fibres then detach from each other creating a visible hairy surface to a section of the timber, as the delignification progresses the structure of the timber section is weakened and therefore Chemical Delignification is regarded as a structural pest of timber in service.
Chemical Delignification damage is most commonly found in timber sections used as roof tile battens of buildings that are located in close proximity to the sea, large chemical factories or major arterial roads that have heavy traffic.
Buildings close to the sea are exposed to salts brought to land by wind and sea breezes and dwellings within five kilometres of the sea are often found to have chemical delignification in their roof tile battens.
Buildings surrounding chemical factories that have chemical delignification would indicate that the air quality where this building is located is influenced by the chemical production process and/or use of chemicals by the adjoining industry. The cost of repair of the chemical delignification damage would need to be taken into account when this damage is found but it also would be prudent to consider the possibility that the air quality in the area may be affected by chemicals and therefore if any health hazards are present that could cause long-term damage to an occupants health.
Buildings found to have chemical delignification that are in close proximity to a major arterial road would often be affected by fumes from vehicles using the adjoining roads.
Chemical delignification generally will not occur to timbers in service that are sealed, painted or well oiled as the lignin is protected from airborne chemical substances.
Therefore as with most timber damage if we can remove the cause of the damage or protect the timber from exposure to the cause of damage the damage will cease. If the damage is initiating the timber section can be painted or oiled to stop further deterioration, where the chemical delignification damage is advanced then replacement of the damaged timbers is needed.
When chemical delignification is found in roof tile battens or rafters then it is recommended not have persons walk on the roof as collapse may occur and therefore a fall could cause bodily injury.
Chemical delignification is more common in species of softwood timbers although certain species of softwood are more prone to damage than others.
Chemical Delignification may only occur after timbers have been exposed to airborne substances for a relatively long period of time, it is not common to find chemical delignification in buildings that are younger than ten years.
The most common timber species that is used in buildings in the Sydney area that we find is damaged by is the Douglas fir otherwise known as Oregon. Douglas fir is an imported timber species that originates in Northern America and Canada.