External Wall Insulation Cost & Savings Calculator UK 2026
Calculate the cost and energy savings of external wall insulation (EWI) for solid-walled UK homes. Includes ECO4 grant eligibility check for low-income households.
Calculate EWI Cost & Energy Savings
Auto-estimated from floor area × 2.5. Adjust for your property.
EWI Cost & Savings Estimate
Estimated EWI Cost Range
Estimated Annual Bill Saving
Estimated Payback Period
ECO4 Grant Eligibility
Estimates are indicative only. Obtain at least 3 quotes from PAS 2030-certified installers. EWI costs vary significantly by location, wall condition, and finish chosen.
Why Solid-Walled Homes Need External Wall Insulation
Around 7 million UK homes have solid walls — mostly Victorian and Edwardian properties built before 1930. These walls have no cavity and lose heat at roughly twice the rate of modern cavity-wall construction. External wall insulation adds an insulating layer directly to the outside of the building, dramatically reducing heat loss and improving comfort.
EWI also improves a property's EPC rating, typically by two bands (e.g. from E to C), which can increase its value and make it easier to let or sell in the future. For eligible households, the ECO4 scheme can fund the entire installation at no cost to the homeowner.
Frequently Asked Questions
How much does external wall insulation cost in the UK?
In 2026, external wall insulation (EWI) for a typical UK semi-detached house costs between £8,000 and £15,000. A larger detached property can cost £15,000 to £25,000 or more. The cost depends on the property size, wall area, chosen insulation thickness, and finish (render, brick-slip or cladding). ECO4 grants can cover the full cost for eligible low-income households.
How much does EWI save on energy bills?
External wall insulation typically reduces heating bills by 25–40% for solid-walled properties, which lose significantly more heat than cavity-walled homes. The exact saving depends on your current energy usage, the thickness of insulation installed, and your heating system. Annual savings of £300–£600 are common for an average semi-detached house.
What is the ECO4 grant?
ECO4 (Energy Company Obligation 4) is a government scheme requiring large energy suppliers to fund energy efficiency improvements for low-income and fuel-poor households. Eligible households — typically those receiving certain means-tested benefits or with a low EPC rating — can receive fully funded or heavily subsidised insulation, heat pumps, and other improvements. Check your eligibility via the government's Simple Energy Advice website.
Do I need planning permission for EWI?
EWI falls under Permitted Development rights for most properties, so planning permission is not usually required. However, listed buildings, properties in conservation areas, and some flats in converted buildings may require consent. The render or cladding finish will also add 80–150mm to the thickness of your walls, which may affect boundary distances.
How long does external wall insulation last?
High-quality external wall insulation systems are designed to last 25–30 years or more with minimal maintenance. The render or cladding finish may require repainting or cleaning every 10–15 years. Most reputable installers provide a 25-year product warranty and the work should be carried out by a PAS 2030-certified installer.