Dry rot – what can you do about it?

When it comes to property issues, few things bring the homeowner out in a cold sweat quite like the words ‘dry rot’.

It has the ring of a death sentence about it, but while dry rot is potentially very serious, there are steps you can take to remedy it. Even better, you can prevent it taking hold in the first place.


What is dry rot?


Dry rot is a specific kind of fungus that gets into timber and causes it to degrade and crumble. Clearly this can be very bad news for the structural integrity of your house, and it looks pretty horrendous too. The wood shrinks and cracks into cube shapes, then falls to pieces.

The fungus spreads rapidly, and it also has a reputation for establishing itself in dark, out of the way places like behind your skirting boards or under your floors, meaning people often miss it until it’s well under way.

Dry rot isn’t really dry. The term has historical origins (some reckon it refers to seasoned, ‘dry’ building timber rather than freshly-cut trees, while others think it comes from the days of wooden boats in dry dock), but the truth is that the wood still needs to be a bit damp for dry rot to flourish. Moisture content of about 20% is ideal for the growth of the fungus.

There’s an additional sting to dry rot, in that insurers often exclude it from home insurance policies, unless it has resulted from an event that you’re insured against (a broken pipe, for example).


What’s the difference between wet rot and dry rot?


They’re different fungi, and they thrive in different conditions. There are loads of kinds of wet rot, but the main thing is that wet rots are all, well, wetter. Your timber needs to be pretty sodden for wet rot to get into it, and if you can get it dried out quick enough then you might well solve the problem. Dry rot, on the other hand, needs a lot less moisture to thrive, so a slow leak or even poor ventilation can be enough for it to get established.

Another significant difference is that dry rot can travel through non-wood materials, like masonry or plaster. It won’t do your brickwork any damage, but it means dry rot is much more invasive and difficult to eradicate than wet rot.

Identifying which kind of rot you’ve got isn’t always straightforward, but there are lots of guides out there, complete with pictures. If in doubt, call an expert.

What are the risk factors?


Damp is the main one. Trouble is, it doesn’t need to be all that damp for dry rot to rear its ugly head. Even condensation build-up can be enough.

As with so many things, the risks are greater in older properties. Rooves or walls might be less watertight, building timber might not be as well dried and treated, and damp courses might be missing or ineffective. The fungus might even already be in there, lying dormant and waiting for conditions to get moist enough for it to flourish.


What can you do about dry rot?


The short answer is probably to call in a specialist as soon as you can. You’re going to need the big guns. The earlier you can catch it, the better.

The first step will usually be to identify the root cause – meaning the source of the moisture – and to fix it. Once that’s done, you can get on with drying the place out. Any treatments you use won’t be effective until this is done.

Depending on how far it’s progressed, you’ll probably have to remove and replace the fungi-infested timbers. There are specialist fungicidal treatments (many of which contain the chemical boron) for any surviving wood, and other materials like masonry and plaster will also need treating. Fungicides can be injected as well as painted, and you may have to strip the plaster off your walls to effectively treat the brickwork underneath.

In short, it’s a messy, extensive and expensive job, which is why you’ll want to make sure you’ve done it properly. But at least it’s fixable, and once you’ve taken all the steps above it’s very unlikely you’ll get it again.

Better still, be vigilant. Look out for any signs of damp (sometimes you can smell it before you can see it), and make sure the wood in your house is dry before the rot sets in. 

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