Updated June 2026 · CW Doors & Windows
How to improve home insulation — windows, doors and the rest
Heat escapes a typical UK home through the loft (25%), walls (35%), windows and doors (20%) and the floor (10%). Here's how to tackle each in priority order — and where windows and doors fit in.
Priority order for insulation upgrades
1) Loft insulation — biggest impact-per-pound. 270mm minimum, easy DIY.
2) Cavity wall insulation — second biggest impact, professional installation.
3) Draught-proofing doors and windows — quick wins for under £100.
4) Replacing single glazing or pre-2005 double glazing.
5) Floor insulation under suspended timber floors.
Where windows and doors fit in
A failed sealed unit loses more heat than a single window's worth of insulation will recover. Fix misted units before upgrading loft beyond 270mm.
Modern A-rated double glazing achieves U-values around 1.2 W/m²K — a 60–70% improvement over single glazing, 25–30% over pre-2005 double glazing.
Front and back doors are often overlooked. A modern composite door with proper seals removes a major heat loss point.
Real Leicester savings
Whole-house replacement of pre-2005 double glazing saves £180–£250 per year. Combined with door replacement and seal upgrades, total saving around £300 per year on a typical 3-bed semi.
Where windows and doors fit in
Loft and wall insulation usually come first because they cover the largest area. Old single glazed or failed double glazed windows are often the next biggest source of heat loss, along with draughty doors.
Composite doors reach U-values of around 1.0 to 1.4 W/m²K, compared with 1.6 to 1.8 for uPVC. Our A-rated windows start from £450 fitted. We will tell you honestly on the survey if your existing frames are good enough to keep.
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