Wet rot is one of the most common timber problems we deal with across Glasgow and Central Scotland. It's a type of fungal decay that attacks timber exposed to prolonged moisture, steadily destroying the wood's structure until it becomes soft, weak and crumbly.
The good news is that wet rot has a simple cause: moisture. If there's no damp, there's no rot. Timber needs to reach a moisture content of around 30% before wet rot fungi can take hold. That means somewhere in your property, water is getting where it shouldn't be.
Understanding what's causing the moisture is essential. Treating wet rot without fixing the source is pointless: any new timber will simply rot the same way. This guide covers the common causes we see in Scottish properties and what to look out for.
Every case of wet rot starts with moisture. Wet rot fungi need timber with a moisture content of around 30% to germinate and grow. For comparison, dry rot can develop at just 20% moisture content, which is why it's considered more aggressive.
Timber in a well-maintained, properly ventilated property typically has a moisture content of 8-12%. For that to climb to 30%, there needs to be a significant and sustained source of water affecting the timber, whether from outside the building or within it.
The causes fall into a few main categories:
"When we survey a wet rot problem, we're not just looking at the damaged timber. We're looking for the moisture source. Fix the cause, fix the problem. Replace the timber without fixing the cause, and you'll be calling us again in a few years."
Blocked, cracked or overflowing gutters allow rainwater to run down walls instead of draining away. This saturates the masonry and any timber built into the walls, including joist ends, lintels and window frames.
Missing or damaged tiles, deteriorated flashing around chimneys, or poorly sealed roof penetrations let water into the roof space. This moisture can affect roof timbers and travel down to affect ceilings and upper floor joists.
Dripping pipes, faulty seals on radiators, leaking water tanks, and poorly connected washing machines or dishwashers introduce moisture directly into the building fabric, often in concealed locations where damage goes unnoticed.
Failed sealant around baths, showers, sinks and worktops allows water to penetrate behind fittings and into floor voids. Even small amounts of water over time can raise timber moisture to critical levels.
Cracked render, defective pointing, porous masonry or failed cavity trays allow rainwater to penetrate through walls. Any timber in contact with the damp masonry, including skirting boards, door frames and built-in joists, is at risk.
When the damp proof course has failed, is missing, or has been bridged by raised ground levels, moisture from the ground travels up through walls. Ground floor timber, including joists, skirting boards and floor plates, is particularly vulnerable.
Inadequate ventilation in sub-floor voids, roof spaces, bathrooms and kitchens allows moisture to build up. Condensation forms on cold surfaces, and timber in poorly ventilated areas stays damp long enough for rot to develop.
Window frames, door frames and fascia boards are exposed to the weather. If paintwork fails or timber isn't properly maintained, rainwater penetrates the wood directly. Wet rot in window sills and frames is extremely common.
Small problems become big ones when maintenance is neglected. A blocked gutter left for a year, a small roof leak ignored, paintwork that hasn't been refreshed: these create the conditions that allow wet rot to develop.
Wet rot tends to develop in specific locations where timber is most likely to be affected by moisture. Knowing where to look can help you catch problems early.
Ground floor timbers are closest to potential rising damp and sub-floor moisture. Floor joists, sole plates, skirting boards and door frames at ground level are all vulnerable, particularly in older properties without effective damp proofing.
Roof timbers can be affected by leaks that aren't immediately visible as water staining on ceilings. Defective flashing around chimneys is a common culprit that may not show obvious signs internally until significant decay has occurred.
Moisture from leaks, splashing and condensation makes these high-risk areas. Floor joists under bathrooms, timber around kitchen sinks, and any wood in contact with plumbing are commonly affected.
Timber built into external walls, including joist ends, lintels and window frames, is at risk from penetrating damp. The timber may be damp for years before decay becomes visible internally.
Wet rot often develops in concealed locations: behind skirting boards, under floors, inside wall cavities. By the time you notice soft timber or a musty smell, decay may be well established. If you suspect a problem, a professional survey can check areas you can't easily see.
Properties in Glasgow and across Central Scotland face particular challenges when it comes to wet rot.
Let's be honest: it rains a lot here. Scotland's climate means buildings are under constant pressure from moisture. Rainwater goods work harder, external joinery takes more punishment, and any defects in the building envelope let water in more frequently. Regular maintenance isn't optional in our climate.
Many Glasgow tenements and Victorian villas have timber that's been quietly absorbing moisture for decades. Original joists, lintels and floor plates may have been damp for years before anyone notices. Older properties often lack modern damp proofing, and construction methods that were standard 100 years ago don't always protect timber the way modern building does.
In tenement properties, roofs and gutters are shared. Getting all owners to agree on repairs can be difficult, and maintenance often gets delayed. Meanwhile, water keeps getting in. A leak that affects one flat's ceiling might be rotting timber in another flat's floor, and neither owner may realise until significant damage has occurred.
"We've been working on Glasgow properties for over 25 years. We understand the particular challenges our housing stock faces, from Victorian tenements to 1970s system-built homes. That local knowledge helps us identify problems quickly and recommend solutions that work for Scottish conditions."
While this guide focuses on causes, it's worth knowing the signs that suggest wet rot may already be present:
If you notice any of these signs, it's important to get a professional assessment. Wet rot won't spread through masonry like dry rot, but it will continue destroying the affected timber as long as moisture is present. The longer you leave it, the more timber needs replacing.
Wet rot and dry rot can look similar to the untrained eye, but they require different treatments. Misdiagnosis can mean wasted money on the wrong approach, or worse, a dry rot outbreak continuing to spread unchecked. If you're unsure what you're dealing with, get a professional survey.
If you've spotted signs of wet rot, or you're worried about moisture problems in your property, we can help. Our PCA qualified surveyors will identify the type and extent of any decay, trace the moisture source, and recommend the right solution.
We've been treating wet rot across Glasgow and Central Scotland for over 25 years. All our work is backed by a comprehensive long-term guarantee.
Fully accredited professionals you can rely on
Don't let it destroy your timber. Our PCA qualified surveyors can identify the problem, trace the moisture source, and recommend the right solution. All work backed by our comprehensive long-term guarantee.
