Retrofitting a Victorian Terraced House in Manchester

Case Study 1: Retrofitting a Victorian Terraced House in Manchester

Scenario A 120-year-old brick-built terraced house in Manchester, UK, undergoing fabric-first energy retrofit. Constraints include listed building consent limitations (no external wall insulation permitted), narrow cavity walls with no existing insulation, and budget caps limiting replacement of all windows at once. The project prioritises cost-effective U-value improvements within heritage constraints.

Given Data

• U-value: 2.4 W/m²·K (existing single-glazed timber sash windows + uninsulated solid brick walls)
• Surface Area: 85 m² (combined window & exposed wall area contributing most to heat loss)
• Temperature Difference: 14 K (design indoor 20°C, winter outdoor design temp −4°C per UK SAP 10.2)

Calculation Using the Heat Loss Calculator formula:

Heat Loss = U-value × Area × ΔT
= 2.4 W/m²·K × 85 m² × 14 K
= 2.4 × 85 = 204
204 × 14 = 2,856 W

Result and Decision The calculated heat loss of 2,856 W confirmed excessive thermal demand — equivalent to running three 1-kW space heaters continuously just to offset envelope losses. Given heritage constraints, the team selected secondary glazing (U-value reduced to 1.7 W/m²·K) for all sash windows plus targeted internal insulation on the coldest north-facing wall (reducing its effective U-value from 2.1 to 0.9 W/m²·K). Post-intervention recalculations projected heat loss reduction to ~1,620 W — a 43% decrease, meeting Passivhaus EnerPHit ‘low-energy’ threshold without compromising architectural integrity.

Lesson Heritage constraints don’t preclude meaningful thermal improvement — targeted interventions (e.g., secondary glazing + strategic internal insulation) deliver disproportionate gains when applied to the highest-loss elements identified by quantitative heat loss analysis.