The hierarchy
- Reduce demand (airtightness, insulation, glazing).
- Improve controls (BMS, zoning, setbacks).
- Decarbonise the residual heat demand (heat pump).
- Generate (solar PV) and store.
What counts
- Loft, cavity, internal or external wall insulation.
- Glazing upgrade (typically double to triple, or single to double).
- Draught-proofing and airtightness.
- Pipe and cylinder insulation.
- Roof renewal where it includes insulation upgrade.
How it moves £/tCO2e
A 30% reduction in heat demand from fabric works typically cuts the heat-pump kW required by 30% and capital by ~25%. That moves a marginal £450-550/tCO2e bid comfortably clear of the £510 Phase 4 ceiling, and would have been essential to pass Phase 3's tighter £325 threshold.
Evidence Salix wants
Heat-loss model before and after fabric, narrative on options considered, justification for what is and is not in scope. Bids that skip the fabric-first narrative are typically queried at portal stage [Salix].