Working file V6
EWI vs IWI cost (UK 2026)
EWI vs IWI cost (UK 2026): side-by-side decision aid with capex, grant treatment, payback shape and surveyor's note.
| Dimension | EWI (external) | IWI (internal) |
|---|---|---|
| £ per m² installed | £110 to £180 | £75 to £130 |
| Thermal performance | Wraps cold bridges; better U-value at the junction | Higher condensation risk at thermal-bridge corners |
| Floor area loss | None | above 50 to 100mm per wall |
| Planning | Conservation area constraints; Article 4 risk | Internal; usually no planning issue |
| PAS 2035 path | B / C | B / C |
Surveyed 1 October 2026. Ofgem cap for 1 October to 31 December 2026 applied (gas 7.97p, elec 26.32p, gas standing 29.68p, elec standing 54.83p). Next scheduled review 25 November 2026 (January cap announcement). [ref V6]
By Oliver Wakefield-Smith, Founder, Digital Signet. Corrections to oliver at digitalsignet dot com.