Condensation and damp in new-build homes
Streaming windows in a brand-new home can feel alarming. Some of it is normal: a new house is full of water from construction that takes months to escape. But new homes can have defects too, and it's worth knowing the difference.
Why new homes are wet
Concrete, mortar, plaster, screed and timber all go into a house wet, or get wet during construction. As the heating comes on and the building dries, that water evaporates into the indoor air — a large amount, over the first year or two. Modern homes are also built much more airtight than older ones, so the moisture doesn't escape through gaps; it relies on the ventilation system.
The result: more condensation than you'd expect, especially in the first winter, and sometimes shrinkage cracks in plaster as it dries.
How to help a new home dry out
- Use the ventilation system as designed. Keep trickle vents open, and don't switch off continuous extract fans or MVHR units. They're quiet and cheap to run for a reason.
- Heat steadily rather than in short bursts; gentle, consistent warmth dries the structure better.
- Open windows for short periods daily, especially in the first months.
- Avoid adding moisture: dry laundry outside or in a vented or heat-pump dryer where possible.
- Consider a dehumidifier during the first winter.
- Leave furniture slightly off walls and avoid filling built-in cupboards on outside walls tightly.
- Hold off on non-breathable decoration such as vinyl wallpaper until walls have dried — builders often advise waiting before redecorating.
When it might be a defect
Drying-out moisture shows up as general condensation that gradually reduces. Report it promptly if you see:
- A damp patch that grows after rain — possible problems with cavity trays, window seals, roof details or render.
- Damp low on walls that doesn't improve, or a wet floor — possible damp-proof course or membrane issues, or a leaking pipe in the floor.
- Mould in the same cold corners every winter — possibly missing insulation or a poorly detailed junction (a thermal bridge).
- Extract fans that don't seem to pull air — use the tissue test from our bathroom guide. Disconnected or crushed ducting is a common snag.
- Water dripping from ceiling fittings — could be a loft duct discharging inside, or a plumbing leak.
Who to contact
New homes in the UK usually come with a builder's warranty for the first couple of years, followed by a longer structural warranty (from providers such as NHBC, Premier Guarantee or LABC Warranty). In the early period, report defects to the developer in writing with photos and dates. Check your warranty documents for timescales, and whether the developer is registered with the New Homes Quality Board's ombudsman scheme.
Keep a humidity log alongside your report — it helps show whether the problem is general drying-out or something specific. Our full assessment can help you document the pattern.