EWI Costs by Property Type
External wall insulation costs £90-£150 per m² installed, depending on material and finish. Total project costs vary by property: mid-terrace £6,000-£10,000, semi-detached £8,000-£15,000, and detached £18,000-£30,000. These figures include scaffolding, insulation boards, mesh reinforcement, base coat, and render finish. Costs are higher for properties with complex detailing, multiple windows, or difficult access.
ECO4 and Grant Funding
The ECO4 scheme has been extended to 31 December 2026. Eligible households (receiving qualifying benefits or with income under £31,000) can receive EWI at zero upfront cost. From 2027, the Warm Homes Local Grant (up to £15,000) replaces ECO4. Towns with high fuel poverty and poor EPC ratings, particularly Wisbech (65-75% homes D-G), Great Yarmouth (19.4% fuel poverty), Lowestoft, and March, have the highest ECO4 eligibility. Only approximately 5% of England's 8.9 million pre-1945 solid-wall homes have any insulation installed.
U-Value Improvements and Materials
Uninsulated solid brick walls have a U-value of 2.1 W/m²K. After EWI with 100mm EPS, this drops to approximately 0.29 W/m²K — an 86% improvement meeting Building Regulations. Material options include: EPS with render (£90-£120/m², thermal conductivity 0.032), mineral wool (£100-£140/m², non-combustible — ideal for high-rise or fire safety requirements), and phenolic/PIR boards (£120-£150/m², thinnest at 60mm to achieve 0.30 U-value, suitable where space is constrained).
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