Author: Oliver Wakefield-Smith, Founder Digital Signet. Reviewed against DfE Sustainability Strategy (Mar 2025) and Education Estates Strategy (Feb 2026). Verified 22 June 2026.
Pre-1919 stock at £380/m2 for a deep fabric package (solid wall internal insulation, roof, suspended timber floors); 1919-1944 at £320; 1945-1976 at £240; 1977-2000 at £160; post-2000 at £90 for top-up only.
Pre-1919 stock at £380/m2 for a deep fabric package (solid wall internal insulation, roof, suspended timber floors); 1919-1944 at £320; 1945-1976 at £240; 1977-2000 at £160; post-2000 at £90 for top-up only.
Heat-pump capacity scales with heat-loss coefficient. A 1976 secondary with no fabric uplift needs a 480 kW ASHP; with fabric reducing the heat-loss coefficient from 75 to 45 W/m2 the same school needs 290 kW, saving £400k of heat-pump CAPEX and removing the DNO upgrade trigger.
Salix PSDS Phase 4 rewards scope that meets PAS 2035 retrofit-coordinator-checked U-values: walls 0.18 W/m2K, roofs 0.13, floors 0.18, windows 1.4 (centre-pane 1.0). Bidding to laxer values reduces the payback-gateway score.
Pre-1944 schools commonly see the steepest CAPEX per m2 but also the steepest kWh saving per pound spent. Hackbridge Primary verified outturn is the canonical Passivhaus comparator.