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Wet and dry rot: two very different problems
Wet rot and dry rot are both fungal decay in timber and they behave completely differently. Wet rot stays where the water is and stops when the timber dries. Dry rot can travel through masonry and behind plaster to reach timber some distance away, which is why it is the one that turns into a major job if it is missed.
Telling them apart
- Wet rot: timber that is darkened, soft and stringy or crumbling, confined to the wet area
- Dry rot: cuboidal cracking, timber breaking into brick shaped blocks across and along the grain
- Dry rot: white or grey cotton wool like growth, sometimes with lilac or yellow tinges
- Dry rot: rust red spore dust, and strands able to cross masonry and plaster
- A distinctive damp, mushroomy smell in an affected cellar, void or roof space
Why dry rot is the serious one
Dry rot can conduct its own moisture along strands, which means it does not have to stay where the water is. It travels through and behind masonry, plaster and voids to find further timber, so an outbreak discovered at a skirting board may already have reached a floor two rooms away or a lintel above. That is why treating what is visible and stopping there is how outbreaks recur.
It also means the extent has to be established before the scope is set. Opening up is often necessary, and it should be targeted: following the strands from the visible outbreak rather than stripping a building on principle. A survey that specifies exactly where to open up saves both money and unnecessary damage.
Wet rot, which is far more common
Wet rot is the ordinary decay of timber that has been persistently wet, and there are several fungi that cause it. It stays local to the moisture, and once the moisture is dealt with and the affected timber is cut out and replaced, that is genuinely the end of it. The overwhelming majority of the rot we find in this region is wet rot around a specific defect: a leaking gutter over a bay, a joist end in a bridged wall, a window sill that has been failing for years.
Because it is localised, the repair is normally carpentry and building repair rather than large scale chemical treatment, and firms that quote for a whole floor or a whole elevation on the strength of one soft joist end should be asked to justify it.
Putting it right
Every case starts the same way: find and stop the water. A rot treatment applied to timber that is still being wetted is a temporary measure with a certificate attached to it. Then the affected timber is cut back beyond the visible decay and replaced, with any adjacent masonry treated where dry rot is confirmed, and the structure ventilated so it stays dry.
DampScan carries out this work under an insured workmanship guarantee, and where it is a repair to a roof, a gutter or a drain rather than a timber treatment, we will say so. Getting the water dealt with is the part that determines whether it comes back.
Get the extent established before the scope is set
Identification, extent so far as it can be determined, the moisture source behind it, and a written report within 24 hours of the visit.
Book a surveyOr call 07386 225526.
Questions
How do I know if it is dry rot or wet rot?
The clearest indicator is cuboidal cracking: timber affected by dry rot breaks into brick shaped cubes across and along the grain, whereas wet rot tends to leave timber stringy, soft and darkened. Dry rot also produces white or grey cotton wool like growth, rust red spore dust, and strands capable of crossing masonry. And crucially, dry rot can be found in timber some distance from the water source, whereas wet rot stays where the wet is.
Is dry rot really that serious?
It is serious in the sense that it can spread beyond the wet area and reach timber elsewhere in the building, which wet rot cannot. It is not a reason to panic, and it is not usually a reason to strip a house. What it does require is proper determination of the extent before work is scoped, because treating only what is visible is how outbreaks recur two years later, and stripping everything is how the bill trebles unnecessarily.
Can rot be treated without replacing the timber?
It depends on how much section has been lost. Timber that is decayed but structurally intact can sometimes be treated in place once the moisture is dealt with. Timber that has lost significant section has to be cut out and replaced, or reinforced, because a chemical treatment does not restore strength. That is a structural judgement and the report should say plainly which category each affected member falls into.