Most advice on improving an EPC rating is written by people who have never done an assessment. It leads with solar panels and external wall insulation, which are the two things almost nobody reading it will actually do. This is the opposite: the cheap, unglamorous measures first, because on the average London property they are what move the score.
Start by finding the paperwork
Before spending anything, spend an hour looking through your files. Where the assessor cannot verify a measure, the methodology requires assuming the worst reasonable case for the property’s age and construction.
That means a cavity filled ten years ago with no certificate is recorded as unfilled. Loft insulation topped up but hidden under boarding is recorded at whatever depth can actually be seen. Producing the documentation costs nothing and can move a rating on its own.
Worth hunting for: cavity wall insulation guarantees, loft insulation receipts, boiler installation and annual service records, window installation certificates, and anything relating to solar panels or a heat pump.
Lighting
The cheapest measure there is. The assessment counts the proportion of fixed light fittings with low-energy bulbs, so swapping the remaining halogens for LEDs is a genuine, if small, gain for the price of a few bulbs. Do it the week before the visit if you like; it counts on the day.
Loft insulation
The single best value structural measure in most houses. The assessment records depth, and the difference between a thin historic layer and a full modern depth is material. If your loft is boarded over an old thin layer, that is worth addressing properly rather than adding another layer on top of the boards.
This one has a real double benefit: it moves the score and it noticeably reduces what you spend on heating.
Heating controls
Underrated, and frequently the best return per pound on a London flat where the walls and windows are not going anywhere. A system with a room thermostat, a programmer and thermostatic radiator valves scores better than the same boiler with no controls at all.
If you have a modern boiler on a bare on/off switch, this is where I would look first.
Hot water cylinder insulation
If there is a cylinder, its insulation is recorded. An old cylinder with a thin jacket, or none, is an easy and cheap fix. A modern factory-insulated cylinder is already fine and needs nothing.
Draught-proofing and the fabric
Cheap, sensible, and it makes the property more pleasant to live in. Be honest with yourself about how much it will move a rating on its own, though — the methodology is not especially sensitive to it. Do it for comfort and bills, and take the score as a bonus.
The bigger measures, and when they are worth it
Cavity wall insulation, where the property has unfilled cavities, is a substantial gain. Replacing a genuinely old and inefficient boiler is another. Both cost real money, and both are usually worth doing on their own merits rather than purely for the certificate.
Solid wall insulation and solar panels will appear on plenty of recommendation lists. They can be transformative for the score. They are also expensive, disruptive, and in a lot of flats simply not practical. Do not let a generated list talk you into one.
A realistic order of work
- Find and produce the paperwork you already have.
- Swap remaining fittings to low-energy bulbs.
- Sort out heating controls if they are missing or minimal.
- Insulate the hot water cylinder if there is one and it is bare.
- Bring loft insulation up to a proper depth.
- Fill unfilled cavities.
- Only then consider the large-ticket items.
Do I need a new certificate afterwards?
You are not obliged to get one just because you have made improvements. But the old certificate is the one sitting on the public register for a buyer or tenant to find, so if you have done meaningful work, a fresh assessment is usually worth it.
If you are close to a band boundary, it is worth asking before you book. Tell me the current score and what you have done, and I will give you an honest view on whether a re-assessment is likely to cross the line — there is no sense paying for a certificate that says the same thing.
Where to go next
What the bands and the score actually mean, and if you let the property, the minimum standard you have to meet.