Wet rot and dry rot are both fungal timber diseases, but they differ in how they spread and how much moisture they need. Wet rot stays near its damp source and requires moisture above 50%, while dry rot (Serpula lacrymans) needs only 20–30% moisture and can spread aggressively through walls and masonry to attack timbers far from the original damp patch.

Timber decay causes some of the most costly and disruptive repair bills a homeowner can face. The two main types of wood rot — wet rot and dry rot — are both caused by fungi, but they behave very differently, spread at different rates, and require different treatments. Knowing which you’re dealing with can save you thousands in unnecessary remediation work.

Characteristic	Wet Rot	Dry Rot
Moisture Requirement	Requires high moisture levels (around 50% or more)	Thrives in lower moisture (20-30%)
Spread	Stays near the moisture source	Can spread extensively through masonry and timber
Structural Damage	Causes localised damage	Can cause widespread, severe structural damage
Signs	Soft, spongy wood; discoloration; musty smell	Shrinking, cracking timber; fruiting bodies; red spore dust
Common Causes	Persistent damp areas from leaks or poor waterproofing	Poor ventilation, damp walls, and leaks

What is wet rot? Signs, causes and how it spreads

Wet rot is a fungal decay caused primarily by Coniophora puteana (also called cellar fungus), though several other fungal species can also cause wet rot. It develops in timber that is persistently exposed to high moisture — typically where the wood moisture content exceeds 50%.

What causes wet rot?

Wet rot requires a sustained source of moisture to establish and continue growing. Common causes and locations include:

• Leaking roofs and gutters — the most frequent cause in older UK properties
• Poorly sealed or rotting window frames — especially timber sash windows
• Basement and crawl space timbers — where ground moisture and poor ventilation combine
• Rising damp — where moisture wicks up through masonry into floor joists and skirting boards
• Plumbing leaks — slow drips behind walls or under floors

Because wet rot is entirely dependent on its moisture source, it does not spread through masonry or dry timber. Remove the water, and the fungus stops advancing. This makes wet rot considerably more containable than dry rot.

How to identify wet rot: 5 signs to look for

Catching wet rot early prevents localised damage from becoming a structural problem. Look for:

1. Soft, spongy timber — press a screwdriver into the wood; if it sinks in easily, rot is likely present
2. Darkened or discoloured wood — affected timber turns dark brown or black, often darker than surrounding wood
3. Longitudinal cracking — the wood splits along the grain and may feel stringy or fibrous
4. Flaking or bubbling paint — a tell-tale sign on window frames and skirting boards; the paint lifts as the timber beneath moves
5. Musty, earthy smell — a persistent damp smell in a confined area, even when no visible water is present

Is wet rot dangerous to your home?

Wet rot is structurally dangerous if left untreated. While it is less aggressive than dry rot and won’t spread far from its moisture source, it progressively degrades the timber’s load-bearing capacity. Floor joists, roof timbers, and structural beams weakened by wet rot can fail, creating safety hazards. The good news is that treating the moisture source usually stops the rot in its tracks.

What is dry rot? The UK’s most destructive timber fungus

Dry rot is caused by the fungus Serpula lacrymans, and it is widely regarded as the most destructive form of timber decay found in UK buildings. Its ability to spread through masonry, plaster, and brick — not just timber — makes it uniquely dangerous and expensive to treat.

What causes dry rot?

Serpula lacrymans requires far less moisture than wet rot fungi — as little as 20–30% wood moisture content — making it capable of colonising timber that appears relatively dry. Common triggers include:

• Poor subfloor ventilation — stagnant, humid air under suspended timber floors is a classic dry rot environment
• Bridged or failed damp proof courses — allowing ground moisture into floor and wall timbers
• Leaking gutters or downpipes — creating persistently damp wall cavities
• Defective pointing or render — allowing rainwater ingress into solid masonry walls

Once established, Serpula lacrymans spreads via a network of fungal threads called mycelium, which can travel through mortar joints, brick, and plaster in search of new timber to colonise. This means the visible damage is often only a fraction of the total infestation.

How to identify dry rot: key signs

Dry rot has several distinctive signs that differ from wet rot:

• Deep cuboidal cracking — the timber cracks both along and across the grain, forming brick-like sections
• Shrinking, brittle wood — the wood feels lightweight and crumbles easily; structural strength is severely compromised
• White or grey mycelium — a cotton-wool or silky white growth on surfaces, turning grey-lilac as it matures
• Fruiting bodies (sporophores) — mushroom-like rust-orange growths that produce red-brown spore dust in large quantities
• Strands (rhizomorphs) — root-like strands on masonry surfaces that transport water and nutrients; these allow dry rot to spread far from its water source
• Strong mushroom or musty smell — distinctively more pungent than wet rot

Is dry rot dangerous to humans and your home?

To your home: Yes — dry rot is extremely dangerous structurally. Because it spreads through masonry and can travel metres from its origin point, by the time it’s visible the infestation is typically extensive. Affected load-bearing timbers lose structural integrity and in severe cases buildings can become unsafe to occupy.

To human health: Dry rot spores and mycelium can cause respiratory irritation, particularly in people with asthma, allergies, or compromised immune systems. Exposure to large quantities of spores during disturbance (such as during removal work) should be avoided. Professional remediation with appropriate PPE is strongly recommended for anything beyond very minor infestations.

Why is it called dry rot if moisture causes it?

Serpula lacrymans gets its common name from the appearance of the timber it attacks, not the conditions that create it. Once the fungus has consumed the cellulose within the wood, the timber looks and feels dry, crumbly, and dessicated — even though moisture triggered the original infection. The name is also partly historical: early observers noted the apparently ‘dry’ appearance of severely affected wood and the name stuck.

Does wet rot turn into dry rot?

No — wet rot and dry rot are caused by entirely different fungal species and one cannot transform into the other. However, the same damp conditions that cause wet rot can also provide the moisture that allows dry rot spores to germinate. It is possible (and not uncommon) to find both types of rot in the same property, which is why a thorough professional survey is important rather than treating only the visible damage.

Wet rot vs dry rot: key differences at a glance

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Characteristic	Wet rot	Dry rot
Causative fungus	Coniophora puteana (most common)	Serpula lacrymans
Moisture needed	50%+ wood moisture content	20–30% wood moisture content
Spread behaviour	Stays near moisture source	Spreads through masonry, brick, plaster
Speed of spread	Slow to moderate	Fast and aggressive
Appearance	Soft, dark, spongy, splits along grain	Cuboidal cracking, white/grey mycelium, spore dust
Smell	Musty, damp	Strong mushroom/musty odour
Structural risk	Localised; serious if left untreated	Widespread; can affect entire structure
DIY treatable?	Minor cases only	Professional treatment required
Treatment cost (UK)	£500–£1,500 typically	£1,500–£5,000+ depending on extent

How to treat wet rot and dry rot

Treating wet rot

Wet rot treatment follows a logical sequence: eliminate the moisture, remove what’s damaged, and protect what remains.

6. Find and fix the moisture source — repair the leak, repoint masonry, improve ventilation, or install a damp proof course. Without this step, rot will return.
7. Assess the extent of damage — use a moisture meter to map affected areas. Probe timbers with a screwdriver to identify soft sections.
8. Remove and replace severely affected timber — decayed sections should be cut out with a 300–500mm margin beyond the visible damage zone.
9. Treat salvageable timber — dry thoroughly, then apply a penetrating fungicidal wood hardener followed by a preservative treatment.
10. Fill and protect — minor cavities can be filled with two-part epoxy wood filler. Apply a boron-based preservative to surrounding timbers as a precaution.
11. Waterproof and monitor — seal or waterproof surfaces where appropriate and check moisture levels periodically for 6–12 months.

Treating dry rot — why professional help is essential

Dry rot treatment is substantially more complex than wet rot treatment because Serpula lacrymans spreads through masonry. DIY treatment almost always fails to address the full extent of the infestation, resulting in recurrence. Professional treatment typically involves:

12. Full structural survey — a specialist will probe, moisture-map, and visually inspect the affected area and adjacent spaces. Expect some opening-up of walls and floors.
13. Removal of all affected material — timber is cut back at least 300–500mm beyond the last visible strand. Affected plaster and render are removed.
14. Masonry sterilisation — masonry surfaces are treated with a biocidal solution (often zinc oxychloride or similar) to kill any fungal threads within the wall.
15. Replacement with pre-treated timber — all replacement timbers must be pressure-treated with a preservative before installation.
16. Ongoing moisture control — ventilation improvements, DPC works, or waterproofing are installed to prevent recurrence.

Note: always obtain a written guarantee from your dry rot specialist. PCA (Property Care Association) member firms offer industry-backed guarantees typically lasting 20–30 years.

What can I do myself vs when to call a professional?

Situation	DIY appropriate?	Recommended action
Small area of wet rot on a window frame	Yes, with care	Sand back, apply hardener, fill, repaint
Wet rot in skirting boards or floor joists	Partial	Fix moisture source yourself; consider professional for timber replacement
Any suspected dry rot	No	Call a specialist immediately
Rot affecting structural timbers (beams, joists)	No	Professional structural assessment required
Basement or crawl space rot	No	Enclosed spaces require professional assessment and treatment

How to prevent rot in your home

Most rot is entirely preventable. These measures address the conditions that allow fungi to establish:

• Maintain gutters and downpipes — blocked or overflowing gutters are the #1 cause of timber rot in UK buildings. Clear them every autumn and after storms.
• Ensure subfloor ventilation — keep air bricks clear of soil, debris, and vegetation. If you have a suspended timber floor, check that airflow is unobstructed.
• Inspect window and door frames annually — paint or sealant failures around frames are an open invitation to wet rot. Re-seal any cracks before winter.
• Monitor with a moisture meter — a basic moisture meter (from £15) lets you check timber regularly. Readings above 20% in wood warrant investigation; above 28% in softwood is considered high risk.
• Address rising damp early — a failed or bridged damp proof course is a slow-motion rot generator. Have it inspected if you notice tide marks on internal walls.
• Ventilate bathrooms, kitchens and utility rooms — condensation in poorly ventilated rooms gradually raises moisture levels in adjacent timber.

Wet rot and dry rot treatment costs in the UK

Treatment costs vary significantly depending on the extent of the damage, access, and location. These are indicative ranges for London and the South East:

Treatment type	Typical cost range	Notes
Wet rot — minor (single window frame)	£200–£500	Often DIY-able
Wet rot — moderate (floor joists/skirting)	£500–£1,500	Professional recommended
Wet rot — extensive (multiple timbers)	£1,500–£4,000	Professional required
Dry rot — minor/early stage	£1,500–£3,000	Professional required
Dry rot — moderate (single room)	£3,000–£7,000	Specialist required
Dry rot — extensive/structural	£7,000–£20,000+	Major remediation works

These figures are estimates only. Always obtain at least two quotes and check that contractors are PCA members or hold equivalent industry accreditation.

FAQ

Does wet rot smell?

Yes. Wet rot produces a musty, earthy smell similar to damp soil or old cellars. The smell is caused by volatile organic compounds (VOCs) released by the fungus as it breaks down wood. If you notice a persistent musty smell in a particular area without an obvious source, probe nearby timber with a screwdriver.

Is dry rot contagious to furniture or clothing?

Serpula lacrymans is specifically adapted to attack structural timber in buildings and will not colonise furniture, clothing, or other organic materials in the same way. However, dry rot spores are present throughout affected buildings and can settle on surfaces. Furniture left in a severely dry-rot-affected room should be cleaned before being moved to a treated area.

Can dry rot spread to other rooms?

Yes — this is what makes dry rot so destructive. Serpula lacrymans can travel through masonry to reach timbers in adjacent rooms, floors, or even separate structures. It has been recorded crossing gaps of several metres through brickwork. This is why professional treatment must address masonry as well as timber.

Does dry rot affect plaster and brick?

Dry rot mycelium and strands can penetrate plaster, mortar, and brick to access new timber. The fungus itself does not consume masonry — it uses it as a conduit. However, the penetration can weaken pointing and render, and affected masonry must be treated as part of any remediation programme.

What is the difference between dry rot and damp?

Damp refers to excess moisture in a building (rising damp, penetrating damp, condensation). Dry rot is a consequence of damp — specifically, Serpula lacrymans fungus growing in timber that has been made damp. Treating damp is necessary to resolve rot, but damp treatment alone will not kill an established dry rot colony.

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Wet and dry rot treatment in London and North London

Damp & Mould Solutions provides specialist timber decay surveys and treatment across North London, including Barnet, Hendon, Edgware, Wood Green, Finchley, Brent, and Haringey. Our surveyors are fully trained in identifying and treating both wet rot and dry rot, and all dry rot treatments carry a written guarantee.

If you suspect you have a rot problem — or you’ve had it confirmed by a survey — contact us for a free initial assessment.

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