Wet rot survey

A wet rot survey answers two questions that nobody can answer by looking: how far the decay actually goes, and what is keeping the timber wet. Until those are settled, any price you are given is a guess, and you have no way of telling a careful quote from an optimistic one.

It is a short, physical piece of work. Somebody comes out, opens up enough to see the timber properly, probes it, takes moisture readings, traces the water back to where it is getting in, and writes down what they found. You get that in writing whether or not you go ahead with any work.

Why the extent matters more than the diagnosis

Most people booking a survey already suspect they have rot. What they do not know is how much. That matters because wet rot damage is nearly always bigger than the part you can see, and for a completely mundane reason: the wet part of a piece of timber is larger than the stained part, and the weakened part is larger than the soft part.

A window sill that looks like a six inch problem at the corner can be soft for a third of its length once the paint comes off. A joist that seems fine where it crosses the room can be fibrous and load-shedding at the end buried in the wall. Agreeing a budget before anyone has established which of those you have is how a five hundred pound repair becomes a two thousand pound one halfway through, with the work already open and no room to argue.

Establishing which rot it is, before anyone prices anything

The first thing worth settling is whether it is wet rot at all. Wet rot, usually Coniophora puteana, stays in the damp timber and dies once that timber dries. Dry rot, Serpula lacrymans, is the only timber fungus in the UK that spreads through masonry and conducts water along its own strands to reach dry timber several metres from where it started. The repairs are not the same size, not the same order of work, and not the same price.

So the surveyor is looking at more than the soft patch. Grey or white sheeting on the back of a skirting, fine orange dust on a sill, cube shaped cracking across the grain rather than long splits along it, and a musty mushroomy smell all point away from wet rot. Getting that call right is the highest value ten minutes of the visit. If you want the differences in detail before anyone comes out, our page onwet rot or dry rot sets them out.

What happens on the visit

1. A look at the whole picture first. Outside as well as in. Gutters, downpipes, hoppers, flashings, the ground level against the wall, airbricks and whether anything has blocked them. In a tenement that includes the shared rainwater goods, because a cracked hopper two floors up is a common cause of a wet joist end on the floor below.
2. Probing with a bradawl. A bradawl or a small screwdriver is pushed into the timber at intervals. Sound wood resists and the point stops. Decayed wood takes it with almost no pressure. Working along the timber this way finds the boundary between soft and sound, which is the line the eventual repair is cut back to. It is low technology and it is the most reliable thing done on the visit.
3. Moisture readings. A meter is used across the timber and the adjoining wall to establish whether the damp is current or historic. Dry timber in an ordinary heated home reads around 10 to 14 per cent. Readings above roughly 20 per cent are high enough for decay to continue, and a wet joist end can read far higher than that. Readings that fall away sharply as you move from the wall tell a very different story from readings that stay high across a whole floor.
4. Opening up where it is needed. A board or two lifted near the suspected damp, a section of skirting eased off, a sill nosing removed. This is agreed with you first and kept to the minimum that answers the question, but a survey that never opens anything is a survey that can only report what you already saw.
5. Tracing the water back. The point is not to record that timber is wet. It is to establish why. A waste pipe under a bath, a failing flat roof, a slipped slate, a rendered-over wall trapping moisture, decking laid across an airbrick. Without this the report is a description rather than a plan.
6. Writing it up. What was found, where, how far it runs, what caused it, what needs doing and in what order.

What the report gives you

• Which fungus it is, or a clear statement that identification needs more exposure
• Whether the decay is active or historic, with the readings behind that call
• How far the affected timber runs, and where it was probed
• The source of the water and what has to happen to stop it
• The remedial work described in an order that makes sense
• What was not accessible, so nobody pretends the whole picture is known

That document does more than justify a repair. It is what you hand to another contractor to get a comparable quote, what you show a lender or a solicitor when a Scottish home report has flagged timber decay, and what you put in front of the other owners in a tenement when the fault is in something shared and nobody wants to be the one who pays for it.

When a survey is worth it and when it is not

If you have a single ground floor window sill, the cause is a cracked bead you can see, and a bradawl tells you the softness stops within a few inches, you probably do not need anybody. Get a joiner. The survey earns its money when the timber is holding something up, when you cannot find the water, when the same repair has failed once already, or when two quotes for the same job are hundreds of pounds apart and you cannot work out why.

Once the extent is known, the wet rot treatment page covers what the work involves, and thecost page sets out the ranges repairs of that size usually land in. If you are not sure yet whether the problem is rot, woodworm or both, a timber survey covers the lot in one visit, which is how most of these actually start.