Rot is common when moisture is present, and can cause significant structural damage.
There are three broad categories of rot.
Brown rot, which can be dry or wet rot, tends to make the timber look darker. It is more common on soft woods and rare in hardwoods.
Timber affected by brown rot can easily be penetrated with a knife, and when the timber is dry, the affected area appears dark and has cross-grain cracks.
Once started, wet rot can continue to grow at lower moisture levels than other rots and will decay timber rapidly. Dry rot can transport the moisture it needs, allowing it to attack even dry timber. It is extremely destructive, so all timber affected by dry rot must be removed completely.
White rot, which is a wet rot only, gives timber a yellowish-white fibrous appearance. It prefers hardwoods and requires moderate to higher moisture levels to grow.
Soft rot may cause timber to darken or appear greyish but cannot always be seen from the outward appearance of the timber. In advanced stages of decay, the timber can easily be penetrated with a sharp knife. Soft rot requires high moisture levels to grow and is more commonly found on timber in contact with the ground.
Rot in timber is most likely to be found around brick chimneys, around windows, on weatherboards on the side of the house most exposed to the weather and in framing or weatherboards close to the ground.
One problem with stucco houses is where water has drained down the back of the stucco but become trapped around the bottom plate, leading to rot of that member, the bottoms of studs and sometimes even the bearer.
When dealing with rotted timber:
- check that the source of the moisture has been identified and remedied
- remove all visible rot
- remove at least one metre of timber past the last visible sign of rot damage as the root system of the rot may be present in apparently sound timber – in some cases, it may prove easier to replace the entire piece of affected timber rather than trying to replace and strengthen a portion
- treat cut timber with a proprietary paint-on preservative.