What ICF is and where it works
ICF systems use hollow EPS or graphite-EPS blocks (typically 300–350mm thick with 50–100mm EPS each side and a 150–200mm concrete core) stacked into formwork that's then filled with reinforced concrete. The EPS stays in place as permanent insulation. Brands: Nudura, Polarwall, Quad-Lock, Logix, ICF Supplies UK. Wall U-value 0.11–0.15 depending on EPS thickness. Airtightness 1–2 m³/h/m² with proper detailing. Best applications: basements (concrete core provides structural and waterproofing benefit), Passivhaus or EnerPHit new builds, exposed sites needing exceptional thermal performance, double-storey extensions where speed and quality matter, and full new dwellings.
Cost breakdown
Blocks (supply): £55–£90 per m² of wall area depending on thickness and brand. Concrete and reinforcement: £45–£75 per m² (rebar £15–£25, concrete £30–£50 by pump). Install labour: £80–£150 per m² for skilled ICF erector — fewer trades on site than blockwork (one team does both leaves and insulation simultaneously). Bracing and props: £15–£30 per m² hire cost. External render or brick slip: £80–£140 per m² depending on finish. Foundation reinforcement: ICF walls heavier than blockwork (concrete core), strip foundations typically need to be 50–100mm wider — add £500–£1,500 to foundation cost. Total turnkey ICF wall £350–£550 per m². Comparable blockwork cavity wall £280–£420 per m².
ICF in London basements
ICF is one of the most cost-effective basement construction methods in London. The reinforced concrete core provides structural retention against ground loads, the EPS provides thermal insulation, and the system is faster to construct than reinforced concrete on traditional formwork (no formwork strip cycle, integrated insulation). Waterproofing: most London basements use BS 8102 Grade 3 (habitable) with a Type C cavity drain membrane internally and a Type A external waterproofing — ICF accepts both. Typical basement ICF rate £550–£900 per m² of wall area including waterproofing and finish — comparable to or slightly cheaper than RC walls with externally applied insulation.
