What is Wet & Dry Rot? Differences and Treatments

It’s been a lovely summer day in the garden until you spot something suspicious. Perhaps it’s a darkened board on your deck or some flaking wood. These signs of wood rot should not be ignored, but they also don’t have to ruin your day. Knowing how to spot and eliminate rot can be a deck saver!

At Trex Protect, we fight the rot problem before it starts by covering your joists, bearers, rim joists, and the edger board with waterproof butyl tape. We also recommend regular inspections of your wood to avoid wood rot and to take proactive measures.

This article covers both wet rot (Coniophora puteana) or dry rot (Serpula lacrymans ) and what to do if you find either. They may sound alike, but they’re actually quite different and will require different approaches. So read on to learn more!

What is Wet Rot?

Simply put, wet rot occurs when high moisture leads to the natural decay of wood. Water feeds and attracts this rot fungus that affects damp timber (decks, around windows, etc.), plaster, wallpaper, and carpets. The fungi break down the wood’s cell walls and feed on its nutrients.

If dampness raises a timber’s moisture content above 20 per cent, wet rot spores will germinate and grow. If a programme of timber treatment is not implemented, wet rot can cause structural failure, especially if it infects structural timbers.

Spotting Wet Rot

Catch wet rot early by inspecting for:

• A damp, musty smell  
• Timber that is cracking and beginning to soften
• A board that moves (or bounces) when you walk over it
• Discoloured or weak timber
• Visible localised fungus growth

Pictures of Wet Rot

Sometimes a visual helps in identification. Check out these photographs of wet rot to know what you’re looking for.

Why Does Wet Rot Occur?

Some common causes of wet rot include roofing defects, plumbing leaks, leaky gutters, leaks around showers or baths, condensation, and/or rising damp penetrating a wall or timber post. It can be more challenging to spot the rot if with painted timber. However, if you press a screwdriver into the timber, and it goes in easily, you probably have an issue.

Wet Rot Treatment

Any repair or remediation cost depends on how severely the timber is affected. If rot is widespread, you will need to replace all affected timbers. The main concern for wet rot is to eliminate the source of the rot: any moisture leakage.

Can I Treat Wet Rot Myself?

If you can find the source of the water causing the rot, you can likely treat and eliminate the rot yourself unless significant damage has been done. Once you’ve addressed the water source, the main concern is to find all the rotten wood and repair or replace it.

Cost of Wet Rot Treatment

Water damage can be your greatest cost, especially if you need to replace a roof or damage caused by a leaking pipe. The cost will be as individual as the situation that led to the wet rot.

What is Dry Rot?

Dry rot, the most severe form of fungal decay, attacks the wood in buildings. Also known as brown rot, dry rot is so named because often the timber appears to be dry, as the fungi target cellulose in the timber’s structure.

Causes of Dry Rot

Dry rot draws strength and moisture from digesting the timber. It requires no other source of moisture once it begins growing. However, for moisture to be in the timber, there is usually a leaking gutter, broken or leaking pipes, an issue with an appliance such as a washing machine, penetrating dampness or poor ventilation.

Identifying Dry Rot

What should you look for in these wood-destroying fungi?

• Splitting and cracking of timber into small cubes
• Darker wood
• Dry or crumbly timber
• Fine, fluffy white mycelium
• Grey-whitish “skin”  
• Soft, fleshy mushroom-like body that looks like a pancake
• Red dust from spreading spores
• Checking out photos online can be helpful in identification.

Pictures of Dry Rot

Dry rot can take many forms, so it’s important to know what you’re seeing. These pictures can aid in your inspection.

Dry Rot Treatment

As with wet rot, the first course of treatment is to eliminate any source of moisture. Next, a professional can assess the severity of the outbreak. Often, this requires removing flooring, walls, or decking boards. Next, it is recommended that any infected timbers be cut back to at least 500 mm beyond the last signs of fungal growth or hyphae strands (the branching filaments that make up the mycelium of the fungus). Also, remove any fruiting body and visible spores. Additionally, clean all areas and sterilise masonry.

Replace affected wood with pre-treated timber. Treat remaining wood with a dry rot treatment fluid; these special fungicides help stop re-infestations. A wood preservative such as Ronseal might also be useful in protecting against future rot. If the damage is not significant, a wood filler and wet rot wood hardener may help fortify timbers, especially around doors and windows.

Dry Rot Treatment Costs

The costs for dry rot treatment are twofold. First, you’ll need to have an assessment with a professional to uncover any signs of damage. A rot survey can cost £200 to £400. Second, repairing the rot will, of course, depend on the damage.

Can I Treat Dry Rot Myself?

Dry rot will likely require a professional. Unlike wet rot which can be eliminated by finding the source of moisture, dry rot will continue growing even when you’ve dried out the area. Once it gets going, dry rot can feed on the moisture in the timber. So as long as you have timber, it has food!

Eliminating the rot will require some experience. A professional will be able to determine if you’re dealing with dry rot or insects like woodworm, which will direct your timber treatment options — insecticide, fungicide, wood removal, etc. Because rot often grows in hidden places, you want to be sure to eradicate it.

In summary, both wet and dry rot can be destructive, but they’re not the same.

• Wet rot is less destructive than dry rot
• Wet rot will stop growing if you can remove the source of moisture.
• Coniophora puteana or wet rot is a cellar fungus
• Dry rot does not need a source of water ingress because it generates moisture through its digestion of timber
• Address both wet and dry rot as soon as it’s found. Dry rot will likely require a professional.