How to read your EPC and fix the biggest losses first

Your EPC looks like a simple A-to-G sticker. In reality it's a ranked list of everything that's wrong with your home — priced, scored, and sitting on a public database anyone can pull up. Learn to read it properly and the retrofit order stops being a guess. Get the sequencing wrong and you can easily spend a quarter of your budget fixing a symptom rather than the cause.

We pull the EPC for every survey across Essex, Suffolk, Kent and Cambridgeshire before we even load the van. Half of the visit is confirming what the assessor logged. The other half is spotting what they missed. Here's the system we actually use on the doorstep.

What an EPC actually shows

Every EPC lodged since 2008 is produced by a Domestic Energy Assessor using the RdSAP methodology — a reduced version of the full SAP calculation DESNZ uses for new-build compliance. It measures the fabric (walls, roof, floor, windows), the heating system, the hot-water setup, and any low-carbon tech like solar PV. It then outputs two numbers that matter: the Energy Efficiency Rating (the big coloured dial, 1-100, graded A-G) and the Environmental Impact Rating (a CO2 equivalent, usually ignored).

The bit most homeowners miss sits on pages two and three: the Recommended Improvements table. Each line shows an upgrade, its indicative cost, the annual bill saving, and the new SAP points it would earn. That is your sequencing blueprint.

The five lines on an EPC that matter

1. Walls

Walls carry 30-35% of heat loss in a pre-1982 home. The EPC will label them "Cavity wall, as built, no insulation" (upgrade candidate), "Cavity wall, filled cavity" (done), "Solid brick, as built, no insulation" (EWI or IWI candidate), or "Solid brick, with insulation" (done). If the assessor logged "unknown", assume as-built — they defaulted to the RdSAP standard because they could not inspect.

2. Roof

Roof line tells you loft depth in mm. Anything under 200mm is a clear top-up job. A room-in-roof entry ("Pitched, insulated at rafters") usually logs at around 100mm of mineral wool — almost always underperforming. A flat-roof entry rarely gets an upgrade score because the RdSAP defaults are generous.

3. Floor

Ground floor is the most under-reported. RdSAP assumes "suspended, as built" for any home built before 1996 unless the assessor could see evidence. A borescope in 30 seconds usually reveals you have zero insulation under a timber floor — a £1,800 job that lifts 6-9 SAP points.

4. Main heating

This is where the biggest SAP swing lives. A non-condensing gas boiler at ~70% efficiency vs a 94% condensing boiler is worth 15+ SAP points alone. An air source heat pump in a well-insulated fabric scores higher still. The EPC indicative cost is usually accurate within ±15%.

5. Hot water

Cylinder insulation level and whether the heating is programmed with a separate hot-water schedule both move SAP. A factory-insulated 80mm-jacket cylinder vs a bare copper one is worth 3-5 points. Cheap fix, big score bump.

The sequence that actually earns points

We have run the numbers on ~200 EPCs across East Anglia in the last 12 months. Here is the upgrade order that consistently returns the most SAP points per pound spent — and crucially, keeps grant eligibility open.

1. Loft top-up to 300mm. £500-£700. Earns 4-8 SAP points. Under ECO4 or GBIS, often fully funded.
2. Cavity wall insulation (if applicable). £700-£950. Earns 8-12 points. ECO4 fully funds if benefit-qualified.
3. Hot water cylinder jacket + timer. £150 DIY. Earns 3-5 points.
4. Boiler upgrade if non-condensing. £2,800-£3,800. Earns 10-15 points. BUS grant does not apply here — save that for the heat pump route.
5. Solid wall insulation (if no cavity). £8-£14k EWI. Earns 12-18 points. Slowest payback but biggest SAP swing.
6. Heat pump replacement (once fabric is up to C). £7-£11k after £7,500 BUS grant. Earns 8-12 points.
7. Solar PV + battery. £9-£13k. Earns 5-9 points and fundamentally changes your bills, even though SAP understates it.

Common EPC errors to challenge

• Loft recorded as 270mm when it is actually 100mm — assessor guessed without going up. Costs you roughly 5 SAP points.
• Wall type logged as "cavity" when it is actually solid (common on 1920s-1930s houses with stretcher-bond brickwork that mimics a cavity). Your grant pathway changes entirely.
• Solar PV missed because the assessor did not see the inverter. You are losing 5-9 SAP points of free score.
• Secondary heating (a wood burner, a fixed electric heater) logged as primary. That can drop the rating by a full band.
• Hot water cylinder marked as "unknown insulation" when it has a factory jacket — another 2-3 points.

Any of those is grounds for a fresh EPC. A lodged EPC costs £65-£90. If you are planning an ECO4 or GBIS-funded job, we often commission a fresh assessment at OMEGA survey stage — the uplift in SAP score from correcting errors can flip your eligibility band.

What we do on an OMEGA survey

We pull the EPC from the EPC Register before the visit. On site we borescope the cavity (if any), lift loft insulation in three spots to verify real depth, check the cylinder jacket and timer, photograph the boiler data plate, and check for hidden solar. We then mark up the EPC with corrections and build a sequenced quote — fabric first, heating second, generation third. You leave with a SAP score projection for each stage, not a bundled "it will go up a bit" promise.

Book a free EPC-led survey

Send us your postcode and we will pull your lodged EPC, annotate it, and bring the sequenced quote to a free home energy survey across Essex, Suffolk, Kent and Cambridgeshire. Book online or ring freephone 0800 229 4094. No cost. No obligation. No pressure.