What an EPC actually tells you

An energy performance certificate, or EPC, is a short document — usually two pages plus a recommendations list — that rates your home from A (most efficient) to G (least). It is produced by an accredited assessor who visits the property, measures rooms, checks the walls, roof, windows, heating system and controls, and then runs those details through a standard government calculation called SAP.

The result is a score out of 100, a letter band, an estimate of your annual energy costs, and an estimate of the carbon dioxide your home produces. Crucially, the EPC describes the building, not the people living in it. It assumes standard heating patterns and occupancy, so it will rarely match your actual bills. Treat it as a fair comparison between one property and another, and a checklist of what could be improved.

EPCs are valid for ten years and are lodged on a national register, so you can look up any past certificate for your address for free.

Reading the bands

The scoring is fairly blunt, but it is worth knowing roughly where you sit and what the next band up looks like in practice.

• Band A (92–100): very efficient — typically high insulation levels, a heat pump or efficient gas boiler, good controls and often solar panels.
• Band B (81–91): efficient. Often a modern home or a thoroughly retrofitted older one.
• Band C (69–80): the practical target for most existing UK homes, and the level many lenders and policy proposals focus on.
• Band D (55–68): where the average British home sits. Reasonable, but with obvious improvements available.
• Band E (39–54): costly to heat. Landlords generally cannot let a property below band E without registering an exemption.
• Band F (21–38) and G (1–20): hard-to-heat homes — often solid-walled, poorly insulated or electrically heated with old storage heaters.

Moving from band E to band D, or D to C, is usually achievable with insulation, draught-proofing and heating controls rather than major building work.

The recommendations section is where the value sits

Most people read the band and ignore the rest. That is a mistake. The recommendations table lists specific measures, each with an indicative cost, an estimated annual saving, and the rating your home could reach if you did the work — individually and cumulatively.

Typical entries you might see include:

• Loft insulation to 270mm — often one of the cheapest ways to gain several SAP points.
• Cavity wall insulation — a quick win for homes built between the 1920s and 1990s with unfilled cavities.
• Draught-proofing around windows, doors and skirting boards — low cost, immediate comfort gain.
• A hot water cylinder jacket and pipe lagging — a few pounds, done in an afternoon.
• Heating controls, such as a programmer, room thermostat and thermostatic radiator valves.
• Solid wall insulation, internal or external — effective but disruptive and expensive, so plan carefully.
• Solar panels or an air source heat pump — big-ticket items that make most sense after the fabric is sorted.

Treat the costs as rough guide prices only. Always get two or three local quotes before committing, and check whether your installer is registered under a recognised quality scheme.

Getting one, and checking it

A domestic EPC typically costs somewhere between £60 and £120, more for large or unusual properties. You need one when you sell or rent out a home, and landlords must meet minimum standards — currently band E for new tenancies and existing ones, with limited exemptions available.

Errors are more common than you would hope. Before accepting a certificate, check the basics:

• Is the wall construction right — cavity, solid, timber frame?
• Has existing loft or cavity wall insulation been recorded?
• Are the glazing type and boiler age accurate?
• Do the floor areas and room counts look sensible?

If something is wrong, you can ask the assessor to correct and re-lodge the certificate. It is worth doing — a wrong wall type can shift your rating by a whole band and make planned work look pointless.

Using it as a retrofit roadmap

The most reliable order of work is fabric first. Reduce how much heat escapes before you think about changing how you generate it.

• Draught-proofing, cylinder lagging and loft topping-up first — cheap, quick, immediate.
• Then walls and floors, which are messier and pricier.
• Then heating: controls, then a boiler upgrade or a heat pump.
• Then renewables such as solar photovoltaic panels and battery storage.

Spreading the work over several years makes the cost manageable, and grants help — the Energy Company Obligation, local authority schemes and zero-rate VAT on insulation and heat pumps all reduce the bill. If you are planning a deep retrofit, think about ventilation at the same time; sealing a home tightly without providing fresh air creates damp and condensation problems. Whole-house systems with heat recovery are worth discussing with a designer.

Where the EPC falls short

The certificate does not know how you actually live. It cannot see whether you run the heating at 22°C all winter, whether the house is empty during the day, or how many people share the hot water. It does not capture whether a room overheats in summer, how a retrofit feels to live in, or the carbon footprint of the materials used.

It also gives limited credit for behaviour — smart controls, careful zoning, drying washing outside. So use your rating as a starting point and a benchmark, not a verdict on your home. A band D house with sensible habits can cost less to run than a poorly used band C one, and the improvements it suggests will still cut both your bills and your emissions over time.