Loft & Wall Insulation Calculator
Calculate how much insulation you need, estimated costs, and annual energy savings for loft and wall insulation. Includes ECO4 grant eligibility guidance.
Home Insulation Guide
Loft Insulation
Loft insulation is the most cost-effective single home improvement in the UK. A loft with no insulation loses approximately 25% of a home's heat through the roof. Installing 270mm of mineral wool insulation (the recommended depth) reduces this to near zero heat loss from the roof. Cost: approximately £300–500 DIY (rolls from builders merchants) for a standard semi-detached. Professional installation: £500–800. Annual saving: £150–200 for a typical semi. Payback: 2–4 years. ECO4 government grant:
Cavity Wall Insulation
Cavity wall insulation fills the gap between inner and outer walls with blown mineral wool, polystyrene beads, or foam. The cavity must be at least 50mm wide and the external wall in good condition. Professional installation (requires specialist equipment) costs £400–700 for a typical semi. Annual saving: £130–200. Payback: 3–5 years. Most UK homes built between 1920–1990 have suitable cavities. A trained assessor can check suitability. ECO4 grant: potentially fully funded for households on qual
Solid Wall Insulation
Solid walls (Victorian, Georgian, pre-1920s properties) cannot have cavity insulation. Options: internal wall insulation (rigid insulation boards lined with plasterboard) or external wall insulation (insulation render or cladding system applied externally). Internal: loses floor space (75–100mm per wall), requires redecoration, moves dew point (condensation risk). External: transforms the appearance, no internal disruption, more thermally effective. Both cost £8,000–20,000 for a typical house —
Insulation and Ventilation
Improved insulation significantly reduces air exchange, which can cause condensation and damp if ventilation is inadequate. Any insulation project should include assessment of ventilation: ensure bathroom and kitchen extractor fans are adequate (minimum 15 litres/second for bathrooms, 30 for kitchens). Trickle vents should not be blocked. In older properties, some air infiltration through gaps is the primary ventilation — sealing all gaps without adding mechanical ventilation creates unhealthy i
Recommended for this calculator