Internal wall insulation cost (UK 2026)
Internal wall insulation cost: published installed cost range with the source against each end, plus how it sits in the PAS 2035 fabric-first sequence.
Cost in 2026
Internal wall insulation cost (UK 2026). The published installed range in 2026 is £75 to £130 per m² installed (publisher and Passivhaus Trust Cost Benchmark v1.3), or £9,000 to £16,000 on a 95 m² Victorian terrace where EWI is ruled out by planning. Both ends of that range are stated rather than collapsed to a midpoint, because the spread reflects real differences in scope, access and grant eligibility rather than installer mark-up.
What drives the spread
- System choice: mineral wool plus VCL vs woodfibre vs aerogel laminated board. Aerogel is the slim option, premium of 60 to 100 percent.
- Heritage detailing: lath and plaster removal, cornice and skirting replacement.
- Internal floor area lost (50 to 100mm per wall) is a real cost not captured in the £-per-m² figure.
- Moisture risk and PAS 2035 Path B / C survey time.
Where it sits in the PAS 2035 sequence
PAS 2035 Path B as a rule, Path C for traditional construction. Retrofit Designer typically required.
Surveyor's notes
Get hygrothermal modelling done before signing IWI on a solid-wall building. The Designer fee is small relative to the risk of internal condensation in a poorly detailed install.