Full room condensation & damp assessment
Six short steps for the room with the problem. It checks for leaks and rain first, then works out which surfaces get cold enough to condense, what's driving it, and which fixes are likely to help — with running costs. Every question has a Not sure option; uncertain answers widen the result instead of being guessed.
Takes about 4 minutes. Nothing you enter leaves your browser.
What this assessment does — and doesn't do
Most damp advice online jumps straight to a product. This tool follows the order building surveyors use: find the cause before choosing the treatment. Historic England, RICS and the Property Care Association make the same point in their joint guidance on investigating moisture — a wrong diagnosis wastes money and can make damage worse.
- Water entry screen. Rain penetration, plumbing leaks, failed glazing seals and ground-level problems are flagged separately because humidity control can't fix them.
- Surface calculation. From your room temperature and humidity we calculate the dew point, estimate the temperature of each cold surface from its construction, and work out the humidity right at that surface.
- Moisture balance. We estimate how much water vapour the room gains (people, laundry, cooking, showers) and loses (ventilation), so we can predict what changes when you alter one of them.
- Scenarios, recalculated together. Savings from separate fixes overlap, so combinations are always recalculated as a package — never added up.
Results are ranges, not single numbers, because many inputs are uncertain. You'll get three separate confidence ratings — for the condensation calculation, the cause assessment and the cost estimate — and the one measurement that would improve the result most. Full equations are on the methodology page.
This is not a survey. If there are signs of structural movement, a roof or plumbing leak, electrical items near water, or anyone's health is affected, get a qualified person to inspect. Renters: see your rights on damp and mould.