London's Victorian and Edwardian housing stock — the majority of inner London's family homes — was built with no insulation, single-glazed windows, and chimneys in every room. The result is typically an EPC rating of D or below. Improving energy efficiency is both a cost-saving and sustainability measure, and increasingly relevant to property values as EPC requirements tighten.
Why Victorian Properties Are Poor Performers
Victorian solid-wall construction (225mm single-leaf brick with no cavity) is thermally poor — a typical U-value of 1.7–2.1 W/m²K, compared to modern cavity wall at 0.18–0.28 W/m²K. The solid walls allow continuous heat transfer from inside to outside with no insulation break.
Combined with single-glazed sash windows (U-value 5.0+ W/m²K), timber suspended ground floors with no insulation, and open chimneys, a typical unimproved Victorian terrace loses heat extremely rapidly in winter.
The Priority Improvement Order
Energy efficiency improvements should be applied in priority order — highest impact first:
1. Heating system upgrade (boiler replacement, controls): An old inefficient boiler replaced with a modern condensing combi or system boiler, paired with programmable controls and thermostatic radiator valves, typically cuts heating costs by 20–30%. The easiest win.
2. Roof insulation (loft insulation): If the loft is unoccupied and uninsulated, adding 300mm of mineral wool between and over the joists is the single highest-impact insulation measure per pound spent. EPC improvement is significant.
3. Suspended floor insulation: Rigid insulation between the ground floor timber joists (accessed from below through the sub-floor void via air bricks, or from above by lifting floorboards). Significant improvement in ground floor heat loss.
4. Double glazing: Replacing original single-glazed sash windows with high-quality double-glazed sash-replacement windows significantly reduces heat loss and draughts. In conservation areas, slim-profile timber double-glazed units are the appropriate replacement.
5. Internal wall insulation (IWI): The most impactful but most invasive improvement — 72–100mm insulated plasterboard on solid external walls. Reduces wall heat loss dramatically. Requires making good, new skirting boards, and disruption.
6. External wall insulation (EWI): Applied to the external face of the walls — typically only viable for render-finish properties or where the external appearance will be changed. Not acceptable in conservation areas without planning permission.
7. Air sealing: Draughts through floorboards, around windows, through letterboxes, and up chimneys can account for 15–25% of heat loss in Victorian properties. Draught-proofing is low-cost and high-impact.
EPC Ratings and Required Improvements
The UK Government has indicated that rental properties will need a minimum EPC rating of C in the coming years. Many Victorian London rental properties are currently D or E. The improvements most likely to achieve C from D or E are:
- Loft insulation (if not already present)
- Heating upgrade to modern condensing boiler
- At least some wall insulation
Cost of Energy Efficiency Improvements
| Improvement | Approximate cost |
|---|---|
| New condensing combi boiler (supply + install) | £2,000–£4,000 |
- Loft insulation 300mm (standard 3-bed terrace) | £500–£1,500 | | Suspended floor insulation (ground floor, 3-bed terrace) | £1,200–£3,000 | | Double glazing (per window, timber sash replacement) | £900–£2,500 | | Internal wall insulation (per m², supply + fit) | £80–£130 |
rcbGroup
rcbGroup delivers energy efficiency upgrades as part of refurbishment programmes — integrating insulation, heating, and window improvements into the renovation sequence for maximum impact and minimum disruption.