Home Retrofit Cost Calculator
Retrofit Cost & Savings Summary
Total Retrofit Cost-
Available Grants-
Net Cost After Grants-
Est. Annual Saving-
Payback Period-
Retrofit Costs by Measure 2025/26
| Measure | Cost | Annual Saving | Payback |
|---|---|---|---|
| Loft insulation | £400–£800 | £200–£300 | 2–3 years |
| Cavity wall insulation | £1,000–£1,500 | £200–£400 | 3–5 years |
| Air source heat pump | £8,000–£15,000 | £400–£800 | 8–15 years |
| Solar panels (4kW) | £5,500–£8,000 | £300–£500 | 10–15 years |
| Double glazing | £4,000–£7,000 | £100–£250 | 20–30 years |
Available Grants
Heat Pump Grant
£7,500
ECO4 Scheme
Free insulation
Home Upgrade
Up to £10k
Smart Export
Solar payments
0% VAT on EE
Until 2027
LA Grants
Varies
How to Use This Calculator
1
Select loft insulation
Top-up or full installation — the cheapest improvement with best payback.
2
Choose wall insulation
Cavity, external, or internal — depends on your wall construction.
3
Select heating upgrade
Heat pumps qualify for the £7,500 BUS grant.
4
Add solar panels
Consider 3-5kW system based on roof size and orientation.
5
Review costs and payback
See total cost, available grants, annual savings, and payback period.
Frequently Asked Questions
How much does a full home retrofit cost?
A comprehensive retrofit of a typical UK home can cost £15,000-£40,000 depending on the starting condition and measures chosen. A basic package (loft insulation + cavity walls + new boiler) costs £5,000-£8,000. A deep retrofit (external walls + heat pump + solar + triple glazing) can exceed £40,000. Government grants can reduce costs by £7,500-£15,000.
What is the Boiler Upgrade Scheme?
The BUS offers £7,500 towards air source heat pumps and £7,500 towards ground source heat pumps. The grant is paid directly to the installer. You must have a valid EPC (any rating) and own the property. The scheme runs until March 2028 with extended funding. Apply through an MCS-certified installer who handles the grant application.
Is it worth insulating an old house?
Yes, insulation is almost always the best first investment. An uninsulated Victorian house can lose 35% of heat through walls and 25% through the roof. Cavity wall insulation (£1,000-£1,500) typically saves £200-£400/year with a 3-5 year payback. Even solid wall insulation (£8,000-£15,000) can save £400-£600/year and significantly improve comfort.
What order should I retrofit in?
The recommended order is: 1) Insulation first (loft, walls, floor) to reduce heat demand, 2) Draught-proofing, 3) Upgrade heating system (heat pump works best in well-insulated homes), 4) Solar panels and battery storage, 5) Smart controls and monitoring. This 'fabric first' approach ensures your heating system is correctly sized for the reduced heat demand.
Are retrofit costs tax deductible?
For homeowners, retrofit costs are not tax-deductible but energy efficiency measures (insulation, heat pumps, solar) are VAT-free until 2027. For landlords, some costs can be offset against rental income. For businesses, the Annual Investment Allowance allows 100% deduction in year one. The zero VAT rate alone saves 20% on qualifying measures.
Official Sources & References
Data verified against official UK government sources. Last checked April 2026.