A damp and timber survey is an inspection that identifies the source of moisture in a building and any decay affecting its wood. Its main job is to separate distinct problems that often look alike — rising damp, penetrating damp, condensation, woodworm and rot — so that the right remedy is matched to the right cause. The output is usually a written report describing what was found, where, and what it means for the property.
What a damp and timber survey investigates
The survey looks at moisture in walls, floors and timber, and at any biological decay that moisture may have triggered. A surveyor will typically inspect skirting boards, floor joists, window reveals, basements and roof voids, since these are where problems tend to concentrate. Accessible timber is checked for signs of insect attack or fungal growth.
The point of the exercise is diagnosis rather than decoration. A reading on its own says little; the value lies in linking a measurement to a visible symptom and a plausible cause. A good report will distinguish between a one-off historic event, such as a past leak that has since dried, and an active problem that is still adding moisture.
Common subjects a survey separates include:
- Rising damp — moisture drawn up from the ground through masonry.
- Penetrating damp — water entering through walls, roofs or around openings.
- Condensation — moisture from indoor air settling on cold surfaces.
- Woodworm and beetle — insect larvae tunnelling through timber.
- Dry rot and wet rot — fungal decay that breaks down wood.
Telling rising damp from condensation
A damp and timber survey is an inspection that identifies the source of moisture in a building and any decay affecting its wood.
These two are the most frequently confused, because both leave damp patches and spoiled decoration. The distinction matters because the remedies are completely different. Rising damp is treated at the wall; condensation is managed through ventilation, heating and lifestyle.
Rising damp is moisture moving upward from the ground through porous masonry where there is no effective damp-proof course (DPC) — a barrier built into the wall to stop this movement. It is generally confined to the lower part of the wall, often up to around a metre, and may leave a "tide mark" of salts left behind as water evaporates. It tends to be consistent rather than weather-driven.
Condensation forms when warm, moist indoor air meets a cold surface and the water vapour turns to liquid. It is most common in kitchens, bathrooms and on cold external walls and window frames. Tell-tale signs include black spot mould, damp that worsens in winter, and moisture that appears at high level or in corners rather than only at the base of a wall. A surveyor distinguishing the two will consider the pattern of the damp, the salts present, the ventilation in the room and the readings taken at different heights.
Timber decay: woodworm and rot
Timber problems usually follow moisture, so they are assessed alongside damp. Two broad categories matter: insect attack and fungal decay.
Woodworm is the common name for the larvae of wood-boring beetles. The visible evidence is small round exit holes and fine powdery dust (frass) where the adult beetle has emerged. The key questions are whether the infestation is active and how far it has weakened the timber. Old holes with no fresh dust may indicate past activity that has ceased.
Rot is fungal and depends on damp wood. Wet rot is the more common form and stays largely where the moisture is; the timber becomes soft, dark and crumbly. Dry rot is more serious because the fungus can spread through masonry and across dry timber in search of more wood, carrying its own moisture. It produces fine strands and, in advanced cases, a fruiting body. A surveyor will look at the extent, identify the type where possible, and trace the moisture feeding it — because treating the decay without removing the water source rarely solves anything.
How readings and findings are interpreted
Surveyors commonly use a moisture meter, a hand-held device that gives an electrical reading indicating relative dampness. These meters are useful as a screening tool but they can be misled by salts, foil-backed plaster and surface conditions, so a high reading is a prompt for further investigation rather than a verdict on its own.
More definite answers can come from deeper testing, such as taking samples of mortar or plaster to measure the actual moisture and salt content. The pattern of readings across a wall — high at the base and falling with height, for example — often tells the surveyor more than any single figure.
A clear report explains not just what was measured but what it means. It should state whether a problem appears active, how confident the diagnosis is, and what is recommended. Where a cause cannot be confirmed without opening up the structure, a careful report says so rather than guessing. Reading the conclusions critically is worthwhile: a finding that recommends extensive treatment should be supported by evidence in the body of the report.
What the cost depends on
The fee for a damp and timber survey varies with the property and the depth of investigation, so figures here are deliberately general rather than fixed. Several factors push it up or down.
- Size and type of property — more rooms and more wall area take longer to inspect.
- Access — exposed joists, accessible cellars and lifted floorboards allow a fuller look; concealed timber may require limited inspection or further visits.
- Scope — a focused check of one damp wall differs from a whole-house assessment covering damp, timber and ventilation.
- Sampling and lab testing — measuring salt or moisture content in samples adds cost but improves certainty.
- Report detail — a brief verbal summary differs from a documented report with readings, photographs and recommendations.
One point worth noting concerns independence. Some inspections are carried out by firms that also undertake remedial work, while others are done by surveyors who do not sell treatment. A reader weighing up findings may wish to consider whether the person diagnosing the problem also stands to benefit from the recommended cure, and to seek a second opinion where the proposed works are extensive.
Last reviewed: June 2026