Retrofit Mistakes
Insulation, sealing or new windows can leave a home damper or no warmer when done without diagnosis. These guides explain why common fixes fail and how to get them right.
Why did my retrofit make things worse?
It is a dispiriting and surprisingly common story: money is spent on insulation, new windows or draught-proofing, and the home ends up damper, stuffier or no warmer than before. The work was not necessarily done badly — but it was almost always done without first measuring how the building actually behaves. A retrofit that ignores moisture, airflow and the order of operations does not just underperform; it can move problems around and create new ones.
Read the guideDid insulating my walls cause damp or mould?
Wall insulation should make a home warmer and drier, and done correctly it does. But damp or mould appearing after insulating walls — especially internally, and especially on older solid-wall homes — is a recognised failure mode. It happens when the insulation traps vapour in the wall, leaves cold thermal bridges where moisture condenses, or reduces ventilation. The cause is in the detailing and the building physics, not the idea of insulation itself.
Read the guideDid making my house airtight cause condensation?
Sealing draughts and fitting airtight windows is sound building physics — but only when ventilation is provided to match. Airtightness without a ventilation strategy is one of the most common retrofit mistakes: the home stops losing heat through leaks, but it also stops losing the moisture it produces, so humidity rises and condensation and mould appear. Airtightness and ventilation are two halves of the same measure, and doing one without the other causes the very problems it was meant to prevent.
Read the guideDo damp-proof injections actually work?
Chemical damp-proof injection is one of the most-sold damp treatments in the UK, and one of the most disappointing — not because the chemistry never works, but because the damp it is sold to treat is usually not rising damp at all. When low-level wall damp is actually condensation, penetrating damp or a bridged damp course, an injected chemical course does nothing about the real source, and the damp returns. Whether injections work depends almost entirely on getting the diagnosis right first.
Read the guideWhy do quick fixes like anti-mould paint keep failing?
Anti-mould paint, plug-in dehumidifiers, a bigger boiler, mould sprays, sealant around a window — these are the quick fixes homes reach for, and they share a common fate: they keep failing because they treat the symptom while the cause carries on. A cold, humid surface that grows mould will keep growing it under the paint; a home that loses heat faster than it is made will stay cold with any boiler. The fix that lasts is the one aimed at the underlying building physics, not the visible symptom.
Read the guideWhy is my cavity wall insulation causing damp?
Damp appearing after cavity wall insulation usually means the fill is doing the one thing the cavity was designed to prevent: bridging the gap so water can cross from the wet outer leaf to the dry inner one. This happens when the wall was not suitable for filling in the first place — too exposed to driving rain, a narrow or debris-filled cavity, or an outer leaf already letting water in — or when the insulation was installed badly, leaving slumped or bridged material. The result is damp patches and mould on internal walls that were dry before. It is a building-physics failure, and the fix is to diagnose what is bridging the water and, often, to extract the insulation and put the wall right.
Read the guideWhy didn't my new insulation make my house warmer?
Spending on insulation and feeling no warmer is a common and frustrating outcome — and it almost always means the insulation, though installed, did not address where the home actually loses heat. The biggest losses might have been somewhere you did not insulate; the new insulation might have left gaps, thermal bridges or air-leakage paths that short-circuit it; or the dominant problem might have been draughts rather than poor insulation in the first place. Heat finds the weakest path, so insulating one element while leaving the real losses open changes little. The way to get the improvement you paid for is to find where the heat goes first, then insulate and seal accordingly.
Read the guideWhy is my house damp after insulating the loft?
Finding damp or condensation appear after insulating the loft is a classic retrofit surprise, and it has two common mechanisms. First, insulating and sealing the ceiling reduces the air leakage that used to ventilate the home through the loft, so indoor humidity rises and condenses in the rooms below unless ventilation is added. Second, the loft itself is now colder — the insulation keeps the house's heat out of the loft — so any moist air that still reaches the loft condenses on the cold roof timbers, and if roof ventilation was blocked by the new insulation at the eaves, the loft can become damp and musty. Both are about moisture and ventilation, not a fault in the insulation.
Read the guideCan new windows make condensation worse?
Yes — new windows can make condensation worse, and it is a common and counter-intuitive outcome. Old, draughty windows let a lot of moisture-laden air escape; replacing them with well-sealed units stops that accidental ventilation, so indoor humidity rises. The condensation that used to form on the cold single-glazed windows (where it was visible and wiped away) now forms instead on the next-coldest surfaces — external walls, corners, behind furniture and in unheated rooms — where it is hidden and feeds mould. The windows did not create the moisture; they removed the ventilation that was managing it, so the fix is ventilation, not regret over the windows.
Read the guideWhy did sealing my draughts make the air feel stuffy?
If the air feels stuffy after you sealed up draughts, you have run into the central rule of airtightness: sealing the uncontrolled air leakage that used to ventilate a home, without providing controlled ventilation to replace it, leaves the air stale and humid. Those draughts, though wasteful of heat, were carrying away moisture, CO₂ and stale air. Seal them and the moisture and CO₂ build up — the air feels stuffy, windows mist, and mould can follow — unless you add deliberate ventilation. The answer is not to undo the sealing (which wastes heat again) but to ventilate properly, so the home is both airtight and well-ventilated.
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