Cavity Wall Insulation Payback Calculator (UK)
Calculate UK cavity wall insulation payback period and lifetime savings. Includes ECO4 free-fitting eligibility and energy bill reduction estimates.
Cavity Wall Insulation Guide (UK)
What Cavity Wall Insulation Is
Cavity wall insulation fills the gap between the inner and outer walls of cavity-built homes (most UK homes built 1920-present). Materials used: blown mineral wool (most common since 2010s). Polystyrene beads (EPS). Polyurethane foam (more expensive, higher performance). Installed by drilling small holes (~22mm) in the outer wall mortar lines, blowing insulation into the cavity, then patching the holes. Whole-house installation typically takes 2-4 hours. Suitability — most cavity-built homes wor
Savings and Performance
Typical annual heating bill savings: detached house: £250-£395 (2023 prices). Semi-detached: £165-£260. Mid-terraced: £105-£170. End-terraced: £155-£245. Bungalow: £110-£180. Lower than peak energy crisis but still meaningful at current gas prices. Performance improvement: U-value of uninsulated cavity wall: 1.4-1.7 W/m²·K. After insulation: 0.5-0.7 W/m²·K. Heat loss reduction through walls: typically 50-65%. As walls represent ~35% of total home heat loss, total heating need reduction: 15-25%.
ECO4 Grant — Free or Reduced Cost
Energy Company Obligation 4 (ECO4): 2022-2026 UK government scheme requiring energy companies to fund energy efficiency in eligible homes. Cavity wall insulation often FREE for eligible households. Eligibility criteria: receiving means-tested benefits (Universal Credit, Income Support, JSA, ESA, Pension Credit, Child Tax Credit, etc.). OR property EPC rating D, E, F, or G (most homes built pre-1990). LA Flex pathway: even some non-benefit households can qualify via local authority referral if th
When It's NOT Suitable
Some homes shouldn't have cavity wall insulation: severe weather exposure (driving rain index high). Some Welsh, Cornish, and Scottish locations. Existing damp or rain penetration problems. Insulation traps moisture, makes worse. Address damp first. Narrow cavity (under 40mm). May not have space for adequate insulation. Cavity already partially blocked. Sometimes happens with older homes. Some non-cavity wall types — would damage building. Concerns about retrofitting: 1-2% of installations cause
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