Rotten wood can be a serious and expensive problem. If you know what to look for though, and catch it early, it doesn’t have to be a disaster.
There are two types of rot - wet and dry - and, while neither is ideal in your home, one is much more worrying than the other.
Caused by one of a number of fungi, wet rot is the most common and least serious kind. The fungus takes hold in damp or wet wood (and plaster), but remains there and doesn’t spread, so it’s usually straightforward to spot and to deal with.
Affected wood feels spongy and soft, and may have turned a different colour to normal, hard wood. Because the rot is caused by exposure to water, the first thing to do is stop the water coming into contact with the wood. Remove the worst of the rot and use a wood-hardening treatment. Then fill on top, building the filler up in layers if necessary. If the rot is widespread, it’s often better to remove all of it and splice in a new piece of wood.
The signs to look out for for dry rot are wood cracking in a cuboidal way, a very musty odour and mushroom-like growths. To treat, you need to begin by stopping the source of the damp and then dry this out. All the affected timber, plus at least 60cm on either side, must be removed. Remaining timber (and walls) must be treated to prevent infection. Any structural woodwork should be replaced entirely.
This isn’t a simple DIY job and is one best left to the professionals.