How EPC Points Are Calculated: The Scoring System Explained
Your EPC score is a number from 1 to 100 based on how much energy your home costs to run per square metre. A score of 100 means almost zero energy costs. The average UK home scores 60 (band D). The score is calculated using SAP (Standard Assessment Procedure), a government formula that looks at your insulation, heating, windows, lighting, and any renewable energy. This guide explains exactly how each element affects your score and which upgrades gain the most points.
The EPC bands
| Band | Score | Typical property | Estimated energy cost/year |
|---|---|---|---|
| A | 92 to 100 | New-build homes with solar, heat pump, triple glazing | Under £500 |
| B | 81 to 91 | Well-insulated new builds or fully retrofitted older homes | £500 to £800 |
| C | 69 to 80 | Government target. Most homes with full insulation and modern boiler | £800 to £1,100 |
| D | 55 to 68 | Average UK home. Partial insulation, older boiler | £1,100 to £1,500 |
| E | 39 to 54 | Below average. Minimal insulation, old heating | £1,500 to £2,000 |
| F | 21 to 38 | Poor efficiency. Pre-1930 uninsulated homes | £2,000 to £2,800 |
| G | 1 to 20 | Very poor. No insulation, old electric heating | Over £2,800 |
Energy costs are illustrative based on a 3-bed semi at Ofgem Q1 2026 rates. Actual costs vary by property size and usage.
Use our EPC improvement planner to see your estimated score and which upgrades would move you into a higher band.
How SAP calculates your score
SAP (Standard Assessment Procedure) is the government methodology maintained by BRE. It calculates the annual energy cost of heating, hot water, lighting, and ventilation per square metre of floor area. The lower the cost per square metre, the higher your score.
SAP does not measure your actual energy bills. It uses standardised assumptions about occupancy, heating patterns, and internal temperatures so that every home is assessed on a level playing field. Two identical homes with different occupants get the same EPC score, even if one household uses more energy.
The calculation considers these elements, roughly in order of impact on the final score.
1. Walls (25 to 35% of score impact)
Wall construction and insulation have the biggest single impact on your EPC score. Solid walls (pre-1930 homes) without insulation are the worst performers. Cavity walls with filled insulation score well. The assessor records the wall type (solid, cavity, timber frame), insulation status (none, partial, full), and wall thickness.
Solid wall insulation (internal or external) can gain 15 to 25 EPC points. Cavity wall insulation gains 10 to 20 points. These are typically the biggest single-measure improvements available.
2. Roof and loft (15 to 25% of score impact)
Loft insulation depth is directly measured. No insulation scores very poorly. 100mm scores moderately. The recommended 270mm scores well. The assessor checks the depth at multiple points across the loft.
Loft insulation to 270mm gains 5 to 15 EPC points depending on what is already there. Going from zero to 270mm is one of the cheapest and highest-impact upgrades. Check if you can get free loft insulation through ECO4.
3. Heating system (15 to 25% of score impact)
Your main heating system's efficiency rating feeds directly into the SAP calculation. An old G-rated boiler (under 70% efficient) drags your score down significantly. A modern A-rated condensing boiler (90%+ efficient) scores well. A heat pump scores best because SAP accounts for the COP multiplier.
Upgrading an old boiler to a condensing model gains 10 to 20 points. Switching to a heat pump gains 15 to 25 points. Adding smart heating controls gains 2 to 5 points.
4. Windows (10 to 15% of score impact)
Window glazing type and age affect heat loss calculations. Single glazing scores poorly. Pre-2002 double glazing scores moderately. Post-2002 double glazing or triple glazing scores well. The assessor records the glazing type, frame material, and approximate installation date for each window orientation.
Upgrading from single to double glazing gains 5 to 10 EPC points but costs £4,000 to £8,000 for a full house. It is one of the least cost-effective ways to improve your EPC score compared to insulation.
5. Hot water (5 to 10% of score impact)
How you heat your hot water and whether the cylinder is insulated matters. An uninsulated hot water cylinder loses significant energy. A well-insulated cylinder (factory-fitted foam jacket) scores well. Combi boilers avoid cylinder losses entirely. Solar thermal panels for hot water boost this element significantly.
6. Lighting (3 to 5% of score impact)
The proportion of low-energy lighting (LED or CFL) in your home affects the score. SAP counts the total number of light fittings and the percentage that are low-energy. A home with 100% LED lighting scores a few points higher than one with mostly halogen or incandescent bulbs.
Switching all bulbs to LED costs under £50 and gains 1 to 3 EPC points. It is the cheapest possible improvement.
7. Renewable energy (bonus points)
Solar PV panels, solar thermal, and wind turbines generate energy that offsets the home's consumption in the SAP calculation. A typical 4 kW solar PV system can add 10 to 15 EPC points. Read Are Solar Panels Worth It? for the full financial analysis.
8. Air tightness and thermal bridging
SAP includes default assumptions for air leakage and thermal bridging (heat loss at junctions between building elements). If a home has been air-tested, the actual result can be used, which often improves the score. Draught-proofing improves comfort but does not directly change EPC calculations unless a post-work air test is conducted.
Which upgrades gain the most EPC points
| Upgrade | EPC points gained | Cost | Points per pound |
|---|---|---|---|
| LED lighting (full house) | 1 to 3 | £30 to £50 | Very high |
| Loft insulation (0 to 270mm) | 5 to 15 | £300 to £600 | Very high |
| Cavity wall insulation | 10 to 20 | £400 to £1,500 | High |
| Heating controls upgrade | 2 to 5 | £150 to £350 | High |
| Hot water cylinder insulation | 1 to 3 | £15 to £30 | Very high |
| New condensing boiler | 10 to 20 | £2,000 to £3,500 | Moderate |
| Heat pump | 15 to 25 | £1,500 to £5,500 (after BUS) | Moderate |
| Solid wall insulation | 15 to 25 | £4,000 to £14,000 | Low |
| Solar PV (4 kW) | 10 to 15 | £4,500 to £6,000 | Low |
| Double glazing (full house) | 5 to 10 | £4,000 to £8,000 | Low |
Points gained depend on starting position and property type. Cost ranges from Energy Saving Trust. "Points per pound" is a relative measure of cost-effectiveness.
The optimal upgrade sequence for most homes is: LED lighting, then loft insulation, then cavity wall insulation, then heating system upgrade. This sequence gives the most EPC points for the least cost. Use our EPC improvement planner to model the exact impact for your property.
Free upgrades first
If you qualify for ECO4, you can get loft insulation, cavity wall insulation, and even solid wall insulation at no cost. Check our grant eligibility checker before spending anything.
How an EPC assessment works
A qualified Domestic Energy Assessor (DEA) visits your property and records every element that feeds into the SAP calculation. The visit takes 45 minutes to 1 hour. They will check loft insulation depth, wall construction type and insulation, window glazing type and age, boiler make, model, and installation date, heating controls, hot water system, number and type of light fittings, and any renewable energy systems.
The assessor enters all this data into SAP software, which produces the EPC score, band, and a list of recommended improvements with estimated cost and savings. The certificate is then lodged on the national EPC register and is valid for 10 years.
An EPC costs £60 to £120. Find accredited assessors on the GOV.UK EPC register.
Common scoring mistakes
The assessor missed your insulation. If cavity wall insulation was installed but the assessor cannot see evidence of drill holes or a guarantee certificate, they may record it as uninsulated. This drops your score by 10 to 20 points. Always provide the insulation guarantee certificate during the assessment.
Loft insulation was patchy. If the assessor can only access one part of the loft and insulation is thin or missing there, they record the lowest depth. Ensure the loft hatch area is representative, or show them multiple access points.
Old extension dragging the score down. If your home has an uninsulated extension, it brings down the whole property's score. Insulating the extension is often a quick win.
Boiler age assumed wrong. If the assessor cannot read the boiler's data plate, they may assume a default (lower) efficiency. Point out the boiler model and installation date. Read our heat pump vs boiler guide if you are considering replacing it.
Track your home's energy performance with a recommended energy monitor to compare actual usage against EPC predictions.
Frequently asked questions
How is an EPC score calculated?
Using SAP, which estimates annual energy cost per square metre. It looks at insulation, heating, windows, lighting, and renewables. Use our EPC calculator for an estimate.
What does each EPC band mean?
A (92 to 100) is best. D (55 to 68) is average. G (1 to 20) is worst. The government target is band C for all homes. See our improvement guide for how to reach C.
Which improvements gain the most EPC points?
Wall insulation (10 to 25 points), heating system upgrade (10 to 25 points), and loft insulation (5 to 15 points). LED lighting and hot water cylinder insulation are the cheapest per point.
Can I calculate my own EPC score?
You can estimate it with our EPC calculator. An official EPC requires a qualified assessor visit (£60 to £120). It is valid for 10 years.
How much does an EPC cost?
£60 to £120. Takes 45 minutes to 1 hour. Find assessors on the GOV.UK register.
Data sources
SAP methodology from BRE. EPC register from GOV.UK. Upgrade costs from Energy Saving Trust. Energy prices from Ofgem Q1 2026 price cap.