How to check if your listed building is suffering from wood rot

Natural wood is a beautiful building material, making period timber-framed homes sought-after by many. However, although it may be lustrous and welcoming, wood is a surprisingly vulnerable material that needs ongoing care to stay strong and attractive over time.

One of the biggest threats to historic homes with timber features is wood rot – both wet rot and dry rot – which can cause significant structural damage and cost thousands to repair. How can you accurately diagnose these problems? Here’s our guide to getting started.

Wet Rot

Wet rot is the general term for certain fungal species that thrive in damp environments and cause damage to timber, plaster, wallpaper and carpets. The most common wet rot fungus is Coniophora Puteana, sometimes known as “cellar fungus”, due it being commonly found in basements and other dark areas like roofs.

What causes wet rot?

Wet rot tends to occur in timbers that have been left damp or wet over a long period of time, making them soft and unstable. The moisture could be due to any number of issues – from excessive condensation in kitchens or bathrooms, leaks in roofing or basement walls, damage drainage or penetrating damp.

How to identify wet rot

It’s often difficult to distinguish between wet rot and dry rot, although this is an essential part of choosing an effective treatment. Professional assistance is recommended to make an accurate diagnosis (a number of companies even uses “rot hounds” to sniff out problem areas). Common indications of wet rot in timber include: a damp or musty smell, darkened patches, a soft or spongy texture, shrinkage, cracked appearance, crumbling, localised fungus growth.

If you’re concerned about paint hiding the symptoms of wet rot, you can perform a simple test with a screwdriver or similar tool. Choose an unobtrusive area of the wood (if you can) and try to ease the point of the screwdriver into the surface. The less resistance you encounter, the more serious the wet rot issue is.

Treating wet rot

Eliminating wet rot and repairing the damage takes several steps. Firstly, it’s essential that the source of moisture is identified and fixed. If this is not a quick job, you could also remove the piece of affected timber to replace once it has been treated.

In most cases, wood suffering from wet rot can be salvaged. Treatment usually involves application of a fungicide while the wood is given the chance to completely dry out, then use a wood hardener. It’s also a good idea to treat nearby timbers that appear unaffected, to prevent future outbreaks. Unfortunately, if the damage is particularly widespread, replacing the timbers with new ones may be the only option.


Dry Rot

Like wet rot, dry rot is caused by certain types of fungus (most commonly “Serpula Lacrymans”), however, it’s considerably more serious than wet rot, due to its ability to spread without moisture. Once it begins to spread, dry rot can cause severe damage the structural integrity of the building. If you are worried about dry rot, it’s best to seek professional assistance to treat it immediately.

What causes dry rot?

Dry rot grows from spores that exist naturally in the air (albeit in relatively small numbers). They only become a problem when they land on a surface that provides the right conditions to germinate – timber with a moisture content of around 20% and access to air. Once the first instances of dry rot occur, they give off more spores that quickly spread and grow, while at the same time spreading as mycelium.

Dry rot can appear quite rapidly in the right conditions, which is why it’s important to prioritise remedial work if an outbreak is spotted. The moisture in the timber that allows for dry rot to develop is usually the result of a building fault of some sort. Therefore, dry rot can be triggered by many of the same things as wet rot, including penetrating damp, poor ventilation and leaking external gutters.

How to identify dry rot

Identifying dry rot in its early stages can be tricky – once it reaches the mycelium stage or has a fruiting body, it’s much easier to spot. In the wood itself, look for similar symptoms as wet rot (shrinkage, brittleness, dark parches) and a signature cracking pattern where the wood appears to be splitting into small cubes. You can also look for the fungus itself, checking for:

• A musty or “mushroomy” odour
• Fluffy, cotton-like mycelium spreading across the wood
• A soft layer growing over the wood, typically off-white with yellow or lilac patches
• Visible mushrooms (known as the “fruiting body”), often resembling pancakes.
• Red “dust” from spores as they spread

Be aware that dry rot can affect masonry as well as timber, particularly if the two are in close proximity.

Treating dry rot

As with wet rot, the first stage of treating dry rot is to find the source of the moisture and fix the fault. It’s then important to determine the scale of the rot. This may involve opening up the affected area, removing plaster/render, lifting floorboards etc.

Typically, infected timbers are going to have to be cut away to at least 50cm past the last visible signs of rot and unaffected timbers should be given a generous dose of dry rot treatment. Any replacement timbers should be treated with a fungicide before installation.

When it comes to the walls and other masonry, use a stiff brush to remove any remaining growths, then sterilise the surfaces with a specialist dry rot treatment for masonry.