Two houses, two very different reasons for the same steamed-up window. Knowing which one you've got changes what actually fixes it.
"My house is damp" covers two genuinely different problems depending on when the house was built, and treating them the same way is why so many quick fixes don't stick.
A typical Victorian or Edwardian terrace has solid brick walls with no cavity, so there's no air gap to break up the cold. Once the room warms up, the wall stays noticeably colder than the air around it. Add a fireplace that's been boarded up rather than properly capped and vented, and a chimney that used to pull a steady stream of air through the house, and you've removed the one bit of passive ventilation the house was actually designed around.
Original sash windows, when they've been draught-proofed rather than replaced, keep a surprising amount of natural air movement compared to sealed uPVC, which is part of why older houses with unmodified sashes are sometimes less damp than the same house with cheap double glazing fitted badly. The mechanism is the same either way though: warm, moist indoor air meets a cold solid wall or a sealed window, and the water has to go somewhere. It ends up as condensation.
Modern estate housing solves the cold-wall problem with cavity insulation and double or triple glazing, which is genuinely better thermally. But it comes with a trade-off: the house is far more airtight than an old terrace ever was. Trickle vents in window frames and a couple of extractor fans are often the only planned ventilation in a new three-bed semi, and they're routinely undersized or switched off by the people living there because they're noisy.
The result is a house that holds onto moisture from cooking, showering and drying laundry for far longer than an older, leakier building would. It's a different mechanism to the cold-wall problem in a terrace, but the same outcome: condensation on the coldest surfaces, usually north-facing bedrooms and bathroom ceilings, and mould that keeps returning no matter how often it's cleaned off.
For an older solid-wall property, insulation upgrades help but rarely solve the problem on their own, because there's still a lot of cold masonry and, often, a badly capped chimney or two acting as an uncontrolled draught. For a newer airtight property, more insulation makes the problem worse, not better, because it tightens the seal further without adding the ventilation that's actually missing.
What both need, for different reasons, is controlled ventilation and humidity management that isn't left to chance, extraction that's actually powerful enough and gets used, combined with dehumidification that keeps the whole property below the humidity level mould needs to grow. That's the bit a survey is for: working out which of the two problems, or which mix of both, your specific house has, before recommending anything.
Book a free, no-obligation survey and we'll tell you honestly what's causing it, not just sell you a fix.
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