Energy Efficiency Renovations in London: What Works, What It Costs, and What Grants Are Available

Understanding where heat is lost is essential to prioritising which improvements will deliver the best return. In a typical unimproved Victorian London terrace:

• **Heat loss breakdown (approximate):**
• •Walls: 35–45% of total heat loss (solid brick walls have very poor insulation — U-value approximately 2.0 W/m²K vs. current standard of 0.18–0.28 W/m²K)
• •Roof/loft: 25–30% (particularly high where loft is uninsulated or under-insulated)
• •Windows and doors: 15–20% (single glazing or old double glazing with failed seals)
• •Floors: 10–15% (suspended timber ground floors with no insulation)
• •Draughts/infiltration: 5–15% (gaps at skirtings, around windows, in floor voids)

**The most impactful single improvement is almost always wall insulation** — because walls represent the largest surface area and the worst-performing element in a Victorian terrace. However, wall insulation is also the most complex and expensive intervention. A pragmatic approach starts with the easiest wins (loft insulation, draught-proofing) and works up to the more complex improvements (wall insulation, heat pump).

• **Loft insulation (where there is a cold loft):**
• The easiest and cheapest insulation improvement. Laying mineral wool (200–270mm depth) between and over the joists in a cold loft is quick, inexpensive, and highly effective.
• •Cost: £400–£1,200 for a typical Victorian terrace (DIY possible; professional installation typical for larger lofts)
• •U-value achieved: approximately 0.16 W/m²K
• •ROI: very high — typically 2–3 year payback on energy savings

Note: if the loft is converted (habitable), insulation is within the rafter structure and was typically installed as part of the conversion.

• **External Wall Insulation (EWI):**
• Insulation boards (typically mineral wool or EPS) applied to the external face of the solid brick wall, finished with a render or cladding system. Dramatically improves wall U-value without reducing internal floor area.
• •Cost: £80–£150/m² installed (materials and labour)
• •Typical rear elevation (4m wide × 6m tall): £3,000–£8,000
• •Full house (all elevations): £15,000–£30,000
• •Planning: requires planning permission in Conservation Areas; may affect party wall junctions
• •U-value achieved: approximately 0.18–0.22 W/m²K

• **Internal Wall Insulation (IWI):**
• Insulation boards applied to the internal face of external walls — either as insulated plasterboard (dot-and-dab) or as a separate studwork system with mineral wool in the cavity. Does not require planning permission. Reduces internal floor area by 80–120mm per wall.
• •Cost: £40–£80/m² (insulated plasterboard) or £60–£100/m² (full studwork)
• •U-value achieved: approximately 0.22–0.28 W/m²K (lower than EWI due to thermal bridging at junctions)
• •Risk: if not specified correctly, can create cold bridges and interstitial condensation. Always use a specialist or follow BBA-certified installation guidance.

• **Floor insulation (suspended timber ground floor):**
• Mineral wool or PIR insulation laid between the floor joists, accessed from below (through a trapdoor or from a crawl space) or from above if floors are being replaced.
• •Cost (from above, floors being renewed): £20–£45/m²
• •Cost (from below, access permitting): £15–£35/m²
• •U-value achieved: approximately 0.18–0.22 W/m²K

**Window replacement:** Replacing old single-glazed timber sash windows with double-glazed alternatives is a significant energy improvement — but at a high cost in London Victorian properties, where sash windows in Conservation Areas must maintain external appearance (typically requiring timber sash replacement rather than uPVC).

• •Timber sash replacement (double-glazed, slim sightlines): £800–£1,800 per window
• •Full house (typically 8–16 windows on a Victorian terrace): £10,000–£28,000
• •Conservation Area: replacement windows must match the original sash profile — slimline double-glazed timber sash is the appropriate specification
• •U-value achieved: approximately 1.4–1.8 W/m²K (vs. single-glazed 5.0+ W/m²K)

• **Secondary glazing (Conservation Area alternative):**
• Fitting a secondary glazing panel on the room side of existing sash windows, rather than replacing the original. Achieves a U-value of approximately 2.0–2.5 W/m²K — not as good as replacement double-glazing, but more acceptable in Conservation Areas and reversible.
• •Cost: £300–£700 per window
• •Full house: £4,000–£11,000

• **MVHR (Mechanical Ventilation with Heat Recovery):**
• As houses become more airtight through insulation improvements and draught-proofing, controlled ventilation becomes essential. MVHR extracts stale air from wet rooms (kitchen, bathroom) and supplies fresh air to habitable rooms, recovering 80–90% of the heat from the extracted air to pre-warm incoming fresh air.
• •Cost: £4,000–£9,000 installed (single-dwelling unit with ductwork)
• •Most effective in: well-insulated, relatively airtight houses post-renovation
• •Less appropriate for: poorly insulated, draughty Victorian terraces without wall or floor insulation improvement

• **Air Source Heat Pump (ASHP):**
• ASHPs extract heat from the outside air and use it to heat the home and hot water. They are most effective in well-insulated homes where the heat demand is low.
• •Cost: £8,000–£15,000 installed (including hot water cylinder, controls)
• •Grant available (Boiler Upgrade Scheme — see below): £7,500 off the upfront cost (2026)
• •Requires: a well-insulated home to work efficiently at low flow temperatures; ideally underfloor heating or oversized radiators rather than standard radiators (standard radiators were designed for gas boiler flow temperatures of 70°C; ASHPs work best at 35–55°C)
• •Less suitable for: poorly insulated Victorian terraces without significant fabric improvements first

• **Boiler Upgrade Scheme (BUS):**
• •£7,500 grant toward an Air Source Heat Pump
• •£7,500 grant toward a Ground Source Heat Pump
• •Applied for by the installer, not the homeowner — ask your installer to apply
• •Check current status at the government's energy website; the scheme has been extended multiple times

• **Great British Insulation Scheme (GBIS) and ECO4:**
• Grants for insulation and heating improvements, primarily targeted at lower-income households and properties with low EPC ratings. Eligibility is income and EPC-linked — not universally available.
• •Check eligibility at Simple Energy Advice (simpleenergyadvice.org.uk)

**Warm Homes Plan:** The government's broader scheme (announced in 2024) for retrofitting low-income households and social housing — primarily targeted at social tenants and lower-income private homeowners.

**London-specific schemes:** The Greater London Authority runs occasional grants and support schemes for energy retrofit. Check the Mayor of London's website and your borough council for current availability.

**VAT reduction:** Energy-saving materials installed in residential properties are subject to 0% VAT (reduced from 5% from April 2022). This applies to: insulation, solar panels, heat pumps, MVHR, draught-proofing, wind turbines, and similar energy-saving products and installation.

**EPC improvement and property value:** A property with EPC rating C or above commands a measurable premium over an equivalent property with rating E or F in London. Research suggests a 5–8% price premium for well-rated properties over poorly-rated equivalents in the same area, and some mortgage lenders offer lower rates for higher EPC-rated properties (Green Mortgages).