Every Energy Performance Certificate gives a property two things: a letter from A to G, and a score out of 100 that sits behind it. Most people look at the letter and stop there, which is a shame, because the score is where the useful information is.
The bands, and what the numbers behind them mean
The letter is just a bucket that the score falls into:
- A — 92 and above
- B — 81 to 91
- C — 69 to 80
- D — 55 to 68
- E — 39 to 54
- F — 21 to 38
- G — 1 to 20
This matters more than it looks. A property on 68 and a property on 55 are both band D, but the first is one point from a C and the second is a long way from anything. If you are trying to decide whether improvement work is worth doing, the score tells you how far you have to travel. The letter does not.
What the score is actually measuring
Here is the part that surprises people most: an EPC is not a measure of how much energy you use. It is a measure of the building, assessed as though a standard household lived in it. Your habits are deliberately excluded.
That is why two identical flats in the same block get the same rating even if one is occupied by someone who heats every room all winter and the other by someone who wears a jumper. It is also why turning the thermostat down before I arrive changes nothing at all.
What the assessment does record is the fabric and the fixed services: wall construction and insulation, loft insulation depth, floor type, window glazing, the heating system and its controls, how water is heated, and any renewables such as solar panels. Everything is measured or evidenced on site rather than estimated.
Why the same house can score differently
Assessors work to a defined methodology, so two competent assessors should land in the same place. Where results genuinely differ, it is almost always evidence.
If I cannot see or verify something, the methodology requires me to assume the worst reasonable case for the age and type of the building. A cavity wall that was filled in 2015 with no paperwork and no way to inspect it gets recorded as unfilled, and the score drops accordingly. Produce the installation certificate and it gets recorded as filled.
This is the single biggest thing homeowners can control, and it costs nothing: find the paperwork before the visit. Cavity wall insulation guarantees, loft top-up receipts, boiler installation and service records, window certificates. Every one of those can be the difference between an assumption and a fact.
The two columns on the certificate
The chart shows a current rating and a potential rating. Current is what the property is now. Potential is what it would be if the recommendations listed underneath were all carried out.
Treat potential as a ceiling rather than a plan. The list is generated from the assessment data, not from a survey of what is practical in your particular building, so it will cheerfully recommend solid wall insulation on a flat where there is nowhere sensible to put it. The recommendations are a starting point for a conversation, not a to-do list.
How long it lasts, and when you need a new one
Ten years from the date of lodgement. It is tied to the property rather than to you, so a certificate from a previous sale is still valid if it is inside that window, and you can reuse it. You are not required to get a new one just because you have made improvements — though if you have done meaningful work, a fresh assessment is usually worth it, because the old certificate is the one a buyer will find on the register.
If you are unsure when your current certificate runs out, the date is printed on it and the record is public on the Gov.uk register.
Where to go next
If you are letting the property, the rating has legal consequences — see what the rules mean for landlords. If you have a score you want to move, the improvements that actually shift it is the more useful read.