How to improve an EPC rating
Insulate first, then heating and controls, then generation. Loft insulation, a hot water cylinder jacket and low energy lighting buy SAP points for a fraction of what windows or a heat pump cost.
Last reviewed 24/09/2026
SAP, the method behind an EPC, scores a property on how cheaply and cleanly it delivers heat, hot water and light. That gives you two levers: lose less heat, and produce the energy you do use more efficiently. Everything that moves the score is one of those two things, which is why some expensive work barely registers and some cheap work matters more than people expect.
The score runs from 1 to 100. Band C starts at 69, band D at 55 and band E at 39. Knowing how many points you actually need is the first step, because it decides whether this is a weekend of work or a retrofit project.
Start with what is cheap per point
| Measure | SAP points | Installed cost | Cost per point |
|---|---|---|---|
| Hot water cylinder insulation | +2 | £20–£60 | £20 |
| Loft insulation to 270 mm | +4 | £100–£350 | £56 |
| Low energy lighting throughout | +1 | £25–£90 | £58 |
| Cavity wall insulation | +9 | £600–£1,800 | £133 |
| Heating controls and TRVs | +3 | £350–£900 | £208 |
Indicative installed costs from EPC recommendation reports for England & Wales, for an average sized property.
Those five measures together are worth about 19 SAP points for somewhere between £1,100 and £3,200. For most band D properties that is more than enough to reach band C, and for many band E properties it gets within touching distance.
The order matters less than the principle: buy the cheap points first. A pound spent on cylinder insulation buys about ten times as much score as a pound spent on cavity wall insulation, and around eighty times as much as a pound spent on new windows.
Then the bigger items
A condensing gas boiler earns around 8 points for £2,200 to £3,600. If the existing boiler is old and non-condensing, this is often the single biggest available jump on a property that is already insulated.
Solar PV at 3 kWp earns around 11 points for £5,000 to £8,000. It is expensive per point, but it is one of the few measures that keeps working on an already efficient home, and it does not depend on the fabric.
Internal solid wall insulation earns around 12 points for £4,000 to £14,000. It is the only realistic route on a solid wall property that is stuck in band E or F, and it is disruptive: you lose wall depth in every room treated, and skirtings, sockets and radiators all have to come off and go back.
An air source heat pump earns around 6 points for £9,000 to £14,000 before grants. That is the most expensive way to buy SAP points in the current methodology, because SAP prices electricity well above gas. Install one for carbon, comfort and long term running costs — not to move a band.
What barely moves the needle
- A new front door. Doors are a small part of the heat loss calculation.
- Replacing already double glazed windows with better double glazing. Around 3 points for £3,300 to £6,500 — over £1,600 a point.
- Draught proofing. It genuinely cuts bills and improves comfort, but SAP gives it very little credit.
- A smart thermostat on its own, without the zoning and TRVs that go with proper controls.
Make sure the assessor can see it
This is where scores are quietly lost. An assessor records what they can see and verify on the day. Where they cannot see something, the software falls back on a default for a property of that age and construction, and the default is usually the pessimistic option.
Cavity wall insulation installed by a registered installer is recorded on a national guarantee register that assessors can check. Loft insulation is visible, if the hatch is accessible and the loft is not packed with boxes. Underfloor insulation and internal wall insulation often are not visible at all, so the invoice and the photographs you took during the work are the only evidence.
Collect it before the assessor arrives: installer certificates, guarantees, invoices, and photographs taken mid-installation showing the material in place.
A worked example
Take a three bedroom semi at SAP 58, band D, with an uninsulated cavity, 100 mm of loft insulation, a bare cylinder and halogen downlights. Cylinder insulation, topping the loft up to 270 mm, lamps and cavity wall insulation come to roughly £745 to £2,300 and are worth about 16 points, taking the score to 74 — comfortably band C.
Now take a Victorian terrace at SAP 44, band E, with solid walls and a working condensing boiler. The cheap measures are worth perhaps 7 points, which leaves it at 51, still band E. Reaching band C means internal wall insulation, and the bill jumps from hundreds to thousands. Knowing which of those two properties you have is the whole planning exercise.
If the property is let
From 1 October 2030 a private rented home in England & Wales must reach band C, within a £10,000 cost cap per property. Spending from October 2025 counts towards that cap, so keep every invoice.
That changes the maths slightly: you are not only buying points, you are also spending a budget that is capped. Cheap measures first preserves headroom under the cap for the expensive measure you may still need.