EPC Improvement Calculator
See how much your home's EPC band and SAP score could improve with retrofit measures. Select your current band, tick what is not yet installed, and get an indicative new score and band.
Find out your real EPC potential
These are indicative estimates. A free EcoHome UK survey gives you a property-specific retrofit plan and checks grant eligibility under ECO4 and GBIS.
Get a free survey →How is this calculated? (Methodology & sources)
The Standard Assessment Procedure (SAP) is the UK government's method for rating home energy performance on a scale of 1–100. EPC bands correspond to SAP score ranges. These estimates are indicative only — your actual EPC rating can only be determined by an accredited Domestic Energy Assessor conducting a formal RdSAP assessment.
EPC band / SAP score thresholds (gov.uk):
| Band | SAP score range | Midpoint assumed |
|---|---|---|
| A | 92–100 | 96 |
| B | 81–91 | 86 |
| C | 69–80 | 74 |
| D | 55–68 | 62 |
| E | 39–54 | 46 |
| F | 21–38 | 30 |
| G | 1–20 | 10 |
Indicative SAP point uplifts per measure (conservative estimates):
| Measure | SAP uplift | Notes |
|---|---|---|
| Loft insulation (to 270mm) | +6 pts | EST / BRE data; assumes none or partial previously |
| Cavity wall insulation | +8 pts | EST; applies to unfilled cavity walls |
| Solid wall insulation (IWI/EWI) | +10 pts | EST; higher because solid walls lose more heat per m² |
| Floor insulation | +3 pts | EST; suspended timber ground floors |
| Double / triple glazing | +4 pts | EST; replacing single glazing |
| Draught-proofing | +2 pts | EST; doors, windows, letterboxes, floorboards |
| Low-energy lighting | +2 pts | 100% LED / low-energy fittings throughout |
| Heating controls / smart thermostat | +3 pts | EST; TRVs + programmer / smart control |
| New condensing boiler | +6 pts | EST; replacing old non-condensing boiler (<70% efficient) |
| Heat pump (ASHP / GSHP) | +5 pts | Indicative; depends on fabric quality and heat emitters |
| Solar PV panels | +6 pts | EST; typical 3–4 kWp system; on-site generation raises SAP directly |
Important caveats:
- SAP uplifts are additive estimates only. Real RdSAP assessments use detailed property data and will produce different results.
- Scores are capped at 100 (band A maximum).
- Measure interactions (e.g. heat pump efficiency on poorly insulated fabric) are not modelled here.
- “Don’t know” band assumes SAP 62 (mid band D), close to the UK stock average.
- Cavity wall and solid wall insulation should not both apply — select whichever matches your wall construction.
Why band C matters: Many mortgage lenders offer preferential “green mortgage” rates for band C and above. Estate agents report band C+ properties sell faster. The government is also consulting on a minimum EPC C requirement for private rented properties.
Sources: gov.uk — Energy Performance Certificates, gov.uk — Standard Assessment Procedure (SAP), Energy Saving Trust — Home Insulation, Energy Saving Trust.
This calculator is for guidance only and does not constitute a formal EPC assessment. For an accurate rating instruct an accredited Domestic Energy Assessor, or request a free survey from EcoHome UK.
Why does band C matter so much?
Selling your home: Research by Rightmove and Zoopla consistently shows band C and above properties sell faster and achieve higher prices than equivalent band D–G homes.
Green mortgages: Lenders including Barclays, NatWest and Halifax offer reduced rates (typically 0.1–0.2% lower) for properties rated band C or above. On a £250,000 mortgage this could save over £250/year in interest.
Private rented sector: The UK government has consulted on raising the minimum EPC requirement for privately rented properties to band C. Landlords with band D–G properties may need to upgrade to continue letting legally.
Lower bills: The average band G home spends around £3,800/year on energy vs around £1,200 for a band C home — a saving of over £2,600/year at typical tariff cap rates.
EcoHome UK specialises in getting homes from band D–G up to band C and beyond, often using grant funding under ECO4 or GBIS, so the cost to you can be reduced or zero.