1. The wall problem
Solid stone walls have a typical U-value around 1.7 W/m²K — modern targets are 0.15. There's no cavity to fill, so you're limited to internal or external solutions.
2. External wall insulation (EWI)
£12,000–£18,000. Most effective thermally but visually transformative. Planning restrictions in conservation areas. Requires TrustMark installer and PAS 2030/2035. Moisture risk if poorly installed.
3. Internal wall insulation (IWI)
£4,000–£10,000. No planning issues. Can be done room-by-room. You lose 80–100mm of width and need to handle window reveals, services and breathable build-up carefully.
4. Other measures
- Loft insulation: £300–£600 — always do this
- Draught proofing: £200–£600 — best first step
- Secondary glazing: preserves originals, cuts heat loss and noise
- Floor insulation: viable where suspended timber floors exist
5. Listed buildings and conservation areas
External EWI is unlikely to be approved. Internal sympathetic approaches preferred. Historic Environment Scotland publishes useful guidance.
6. Heat pumps in stone homes
Insulate first, or your heat pump will run inefficiently and cost more to operate. A well-insulated stone home is an excellent heat pump candidate.
7. Grant support
- HES: up to £7,500 grant + £7,500 loan per measure
- Rural uplift for qualifying postcodes
- Warmer Homes Scotland for eligible households
- ECO4 for benefits households
- Council area-based schemes
8. Practical sequence
- Draught proof
- Loft insulation
- EPC assessment
- Internal wall insulation
- Heating upgrade