Which insulation measure makes financial sense in your home? Real BRE/EST saving fractions, broken down by construction era and fuel type.
Calculates the breakeven point for the most common insulation upgrades — loft, cavity wall, solid wall (internal/external), suspended floor — based on your home size, current heating type, and the install cost. Uses U-value uplifts from BRE/EST and current 2026 energy prices.
Insulation is the single most measurement-led intervention. We use the standard heat-loss equation Q = U × A × ΔT × hours, then compare gross fabric loss before and after. No rebate spin.
Home
Heating
Measure
Result
Tell us about your home
Terrace
Semi-detached
Detached
Bungalow
Flat
Pre-1919 (solid wall)
1919-1944
1945-1980 (cavity wall)
1981-2002
2003+ (already insulated)
How do you heat the home?
Mains gas
Oil
LPG
Direct electric
Heat pump
Just the heating portion — for typical UK homes this is £1,200–£1,800 with gas, much higher with oil or direct electric.
Which measure are you considering?
Loft (≥270mm)
Cavity wall
Internal solid wall
External solid wall
Suspended floor
Triple glazing
If you don't know, use our typical mid-range guide. Loft: £400–£700 · CWI: £600–£1,200 · IWI: £4,000–£10,000 · EWI: £12,000–£25,000 · Floor: £2,000–£4,000 · Triple glazing: £8,000–£18,000.
How we model this. Saving fractions per era + measure follow Energy Saving Trust 2024 retrofit guidance and BRE Domestic Energy Fact File. Cavity wall on pre-1919 returns 0% — most pre-1919 homes have no cavity. Cumulative saving uses 3%/year energy price inflation. CO₂ uses 2026 UK grid intensity for electricity (0.21 kg/kWh) and standard combustion factors for fossil fuels. This calculator does NOT replace a PAS 2035 retrofit assessment — solid wall and whole-house projects require professional design to avoid moisture problems.