Wet Windows in a Brand-New Home
New windows, new insulation, new everything — and yet the glass streams every morning. That surprises a lot of first owners, but a new house starts life carrying water that was built into it.
Where the water comes from
The UK Centre for Moisture in Buildings guide Moisture in New Homes (published by NHBC) notes that concreting, screed floors, bricklaying, plastering and painting can put up to 8,000 litres of water into a home’s materials during construction. That moisture dries out steadily, much of it outdoors, but some passes through the indoor air — and indoor air meets the coldest surface it can find: the glass.
How long it lasts
The same guide says to expect a new home to reach a moisture-balanced state within about 18 months to 2 years, and that it should then be free of mould, dampness or excessive condensation. A New Zealand BRANZ bulletin on construction moisture likewise says new houses can see high internal moisture for up to two years. So a wet first winter is common; a wet third winter is a signal to investigate.
What helps while it dries
- Use the ventilation you were given. New homes are built fairly airtight, so the mechanical system does the moisture removal. Read the builder’s handover notes; run extract fans longer or use a boost setting during showers and cooking.
- Keep trickle vents open if your windows have them — the NHBC guide says they should stay open.
- Heat evenly. Steady heat dries materials gradually; big swings leave cold glass for vapour to land on.
- Don’t stack extra moisture on top of construction moisture: avoid drying laundry indoors and keep lids on pots during this period.
- Air out briefly when there is obvious excess moisture — a few minutes with windows open, if safe.
- Wipe sills each morning so water doesn’t sit on new trim and drywall returns.
When it’s not just drying
If condensation gets worse over time instead of better, shows up with mould, or is confined to one spot, ask the builder to check for leaks, blocked vents, or a ventilation fault. Building Science Corporation’s moisture-control digest points to cold spots at wall/ceiling junctions, exterior corners and poorly insulated window headers as common mould locations, and suggests keeping indoor RH around 30% or lower at 21 °C in cold-climate heating months. A hygrometer makes it easy to tell whether you’re near that line.
Sources: UK Centre for Moisture in Buildings / NHBC, Moisture in New Homes; BRANZ, Dealing with construction moisture; Building Science Corporation, BSD-012.
Originally published at https://dry-glass-notes.surge.sh/articles/new-home-construction-moisture-window-condensation.html (AI-assisted, sources cited). If this helped, zaps go to hollisvarrow3753@coinos.io.
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