Looking for a reliable window condensation fix? Condensation on windows is the most common damp problem in UK homes, affecting an estimated 1 in 3 properties. Left untreated, it leads to black mould, peeling paint, rotting window frames, and health issues. The good news: most condensation problems can be solved with straightforward improvements to ventilation, heating, and insulation. This guide explains the causes, compares solutions (from extractor fans to double glazing and dehumidifiers), and provides costs for each approach. Visualise exterior improvements on your home with our free AI colour visualiser.
Why condensation forms on UK windows
Condensation occurs when warm, moisture-laden air contacts a cold surface. In UK homes, single-glazed windows and poorly insulated solid walls create cold spots where warm indoor air dumps its moisture. Cooking, showering, drying clothes indoors, and even breathing produce 10-15 litres of moisture per day in a typical household. When ventilation is inadequate — common in draught-proofed or sealed homes — this moisture has nowhere to go except onto the coldest surface: your windows.
The problem is worse in cavity wall homes with failed cavity wall insulation (which traps moisture instead of preventing it) and in older properties with solid walls that lack any insulation. Penetrating damp and rising damp compound the issue by adding moisture from outside. A damp survey with a moisture meter and salt analysis can distinguish between condensation, penetrating damp, and rising damp — each requiring a different fix.
Window condensation fix: solutions compared
| Solution | Cost | Effectiveness | Best For |
|---|---|---|---|
| Extractor fans (kitchen/bathroom) | £150 – £400 | High | Wet rooms, targeted ventilation |
| Trickle vents / air bricks | £50 – £150 per unit | Moderate | Background ventilation |
| PIV system (Positive Input Ventilation) | £500 – £1,200 | Very high | Whole-house condensation |
| Double glazing upgrade | £350 – £700 per window | Very high | Single-glazed homes |
| Secondary glazing | £100 – £350 per window | High | Listed buildings, sash windows |
| Dehumidifier | £150 – £400 | Moderate | Quick fix, rented properties |
| External wall insulation (EWI) | £80 – £150 per m² | Very high | Solid wall homes, long-term fix |
Ventilation: the first line of defence
Improving ventilation is the most cost-effective window condensation fix. Humidistat-controlled extractor fans in kitchens and bathrooms activate automatically when moisture levels rise. Trickle vents fitted to window frames provide continuous background ventilation without significant heat loss. Air bricks in external walls ventilate suspended timber floors and prevent moisture build-up beneath the DPC (damp proof course). For severe whole-house condensation, a Positive Input Ventilation (PIV) system gently pressurises the home with filtered air, pushing stale, moist air out through natural leakage points.
Double glazing and secondary glazing
Replacing single glazing with double glazing raises the inner glass temperature, dramatically reducing condensation. Modern double glazing achieves U-values of 1.2–1.4 W/m²K compared to 5.8 for single glazing. This eliminates the cold surface problem. For listed buildings and conservation areas where external alterations need planning permission, secondary glazing offers a similar benefit without changing the building's appearance. Both options improve energy efficiency and reduce heating bills, positively impacting your EPC rating.
External wall insulation to prevent condensation
For solid wall properties (common in pre-1930 UK homes), EWI (external wall insulation) is the most comprehensive long-term window condensation fix. By wrapping the building in insulation, wall temperatures rise above the dew point, eliminating condensation on both walls and windows. Breathable render systems like K Rend silicone render or Weber lime render allow moisture vapour to escape while keeping rain out. EWI also addresses thermal bridging, improving your EPC energy rating by 1-2 bands.
Funding is available through the ECO scheme and Green Homes Grant successors. A damp specialist should inspect for rising damp or penetrating damp before installing EWI, as trapped moisture behind insulation causes worse problems. Building regulations (Part L) require minimum thermal performance standards for any retrofit work. Costs range from £80 to £150 per m² including scaffolding, with a typical semi-detached house costing £8,000–£15,000. The guarantee should cover at least 25 years.
Preventing mould from condensation
Black mould thrives in damp, poorly ventilated areas. Once condensation is addressed, treat existing mould with a fungicidal wash, allow surfaces to dry completely, then apply a mould-resistant primer before repainting. Dulux Trade and Permagard produce specialist anti-mould paints. Sovereign damp-proofing products are widely available through builders' merchants. For persistent problems, commission a full damp survey from a BBA-certified damp specialist.
For related guides, see damp proofing exterior walls UK guide, interior decorator cost UK, and painter decorator costs.
Visualise exterior improvements
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