Condensation knowledge hub
Everything you need to understand condensation, damp and mould in a UK home, written in plain English and checked against UK building guidance. Start with the basics, or jump to the room that's giving you trouble.
The basics
How condensation works, in plain English.
Room by room
Why each part of the home gets damp in its own way.
Bedroom condensation
Wet windows every morning? What happens overnight and how to fix it.
Bathroom condensation
Test your extractor fan, run it long enough, and stop ceiling mould.
Loft condensation
Dripping roof felt and mouldy rafters — causes and fixes.
New-build damp
Why new homes stream with condensation — and when it's a defect.
Fixes & ventilation
What actually reduces moisture, and what doesn't.
Reference
Definitions and quick answers.
Guides and tools
Ready to look at your own home? These pages go further on specific problems and let you run the numbers.
Damp or condensation?
Tell condensation apart from rain penetration, leaks and ground moisture before spending money.
Window condensation
Inside, between the panes or outside — what each one means.
Black mould on walls
Why it grows where it does, cleaning it safely, and stopping it coming back.
Renters' rights
Reporting damp and mould, and where to go in each UK nation.
Full room assessment
Our free tool: checks for leaks, finds the cold surfaces and compares fixes.
Dew point calculator
The temperature at which your room air starts to condense.
How we write these guides
We don't sell damp treatments, ventilation units or insulation. Our guidance follows UK sources — including Historic England, the Energy Saving Trust, the UK Health Security Agency, BS 5250 and the Building Regulations approved documents — and our calculations are published on the methodology page. Where evidence is uncertain, we say so. Spotted something wrong? Tell us.