Condensation & Moisture
Condensation is humid air meeting cold surfaces below the dew point. It's a fixable balance of moisture, ventilation and surface temperature.
Why do I have condensation on my windows?
Condensation on windows is the visible result of two things meeting: humid indoor air and a cold glass surface below its dew point. It is a building-physics problem with a clear cause — and a clear, lasting fix.
Read the guideWhy are my windows wet in the morning?
Windows that are wet every morning are showing overnight condensation. While you sleep, the glass cools to its lowest and you add moisture to the air by breathing — so by dawn the air at the glass tips past its dew point.
Read the guideWhy is there moisture on my walls?
Moisture on a wall has three possible mechanisms — condensation, penetrating damp or rising damp — and they look similar but need completely different remedies. Diagnosing which one you have is the single most important step.
Read the guideWhy is condensation worse in winter?
Condensation gets worse in winter for two reasons working together: surfaces are much colder, and homes are closed up so indoor humidity rises. Both push the air at cold surfaces past its dew point.
Read the guideHow do I stop condensation in my home?
Stopping condensation for good means tackling the two things that cause it together: too much moisture in the air and surfaces cold enough for that moisture to condense on. Wiping windows, running a dehumidifier or opening a window now and then treats the symptom briefly. The lasting fix is to lower indoor humidity with controlled ventilation and to warm the cold surfaces, so the air no longer reaches its dew point indoors.
Read the guideWhy do I get condensation in my bedroom?
Bedrooms are one of the most condensation-prone rooms because, overnight, three things combine: we add a surprising amount of moisture to the air just by breathing and perspiring, the room cools as the heating goes off, and the door and windows are usually shut so the moist air cannot escape. Humid air then meets the cold windows and walls and condenses, which is why you so often wake to wet windows and damp patches. It is a balance of moisture, temperature and ventilation, and each can be adjusted.
Read the guideDoes drying clothes indoors cause condensation?
Yes — drying clothes indoors is one of the biggest hidden sources of moisture in a home, and a very common cause of condensation, damp and mould. A single load of wet washing releases a couple of litres of water into the air as it dries, and if that moisture is not ventilated away it raises humidity throughout the home and condenses on the coldest surfaces. It does not mean you cannot dry clothes inside, but it does mean doing so needs ventilation, or the moisture will show up as condensation elsewhere.
Read the guideWhy do I get condensation in an unused or cold room?
An unused or unheated room often gets condensation precisely because it is cold: its surfaces sit well below the temperature of the rest of the home, while moist air from the heated, occupied rooms migrates into it and condenses on those cold walls and windows. Closing the door and turning off the heating to 'save energy' tends to make it worse, not better, because it creates the coldest surfaces in the house with no ventilation to remove the moisture that still finds its way in. The cure is gentle warmth and ventilation, not closing the room off.
Read the guideWhy has condensation suddenly got worse in my house?
When condensation suddenly gets worse, something in the balance that controls it has changed. Condensation forms when humid indoor air meets surfaces below the dew point, so a sudden increase means either there is more moisture in the air, the surfaces have got colder, or the ventilation that used to remove the moisture has reduced — and often a specific, identifiable change is behind it. Colder weather, a new household routine, a broken extractor, draught-proofing or new windows, or a recent retrofit can each tip the balance. Rather than treating the symptom on the glass, the useful question is what changed, because finding the trigger points straight to the fix.
Read the guideHow do I stop condensation in my bathroom?
Bathroom condensation is one of the most common and most solvable damp problems, because the moisture has a clear source — showering and bathing — and the answer is to remove it at source before it spreads and condenses on the cold walls, ceiling, mirror and window. The key is effective extraction that actually clears the steam, run for long enough, combined with keeping the surfaces warm enough not to condense. Where a bathroom keeps misting up and growing mould, it is usually because the extraction is too weak, badly placed or not run long enough, the room is cold, or moist air is escaping into the rest of the home — all of which can be put right.
Read the guideWhy is there condensation on my walls and ceiling?
Condensation on walls and ceilings — not just windows — is a sign that those surfaces are cold enough to fall below the dew point of the indoor air, and that the air is humid enough to deposit moisture on them. It is more serious than window condensation because walls and ceilings are absorbent and harder to wipe, so the moisture soaks in and feeds mould. It points to two things together: surfaces that are too cold (from missing insulation, thermal bridges or unheated rooms) and humidity that is too high (from too little ventilation). The fix is to warm the surfaces and lower the humidity, not to treat the wall as 'damp'.
Read the guideWhy do my windows only get condensation in some rooms?
Condensation appearing on the windows of some rooms but not others is normal and informative: it reflects differences between those rooms in moisture generation, heating and ventilation. The rooms that mist up are usually those that are more humid (bedrooms, where breathing overnight adds moisture; bathrooms and kitchens, where water vapour is generated), cooler (so the glass is colder), or less ventilated (so the moisture isn't removed). The dry rooms simply have a better balance of those three factors. Reading which rooms condense, and why, points straight to the fix — usually more ventilation and warmth in the affected rooms.
Read the guide