D to C is the jump most people need, and it is usually achievable. The trick is knowing which measures the calculation actually rewards on your kind of property, rather than working through a generic list.

Start with what the calculation cares about

The assessment is a model, not a measurement. It rewards things it can evidence: insulation depth, heating efficiency, controls, glazing, and how much of your home is exposed to the outside. It does not reward draught excluders, thick curtains, or a smart meter.

In rough order of value

  1. Loft insulation to current depth. Cheapest meaningful move by a distance, and the calculation is very sensitive to it. If you have 100mm up there, topping to 270mm is the best value work available.
  2. Heating controls. A room thermostat, thermostatic radiator valves and a cylinder thermostat together are inexpensive and score better than most people expect.
  3. A modern condensing boiler if yours is old. Big improvement, big cost — worth doing when the boiler is due anyway rather than for the certificate alone.
  4. Cavity wall insulation — if you have a cavity. Excellent value where it applies.
  5. Glazing. Real but expensive per point, and often restricted in conservation areas.
  6. Solar PV. Moves the rating substantially, but the payback is a separate conversation from the certificate.

The London caveat that changes the list

Most homes built before about 1920 — which is most of inner London — have solid nine-inch brick walls with no cavity. Cavity wall insulation, which sits near the top of every generic list, is simply not available to you. Internal wall insulation is the equivalent, and it is a disruptive, expensive job that eats room space.

If you live in a converted flat, the picture changes again: your neighbours' heated homes above, below and either side are not heat-loss surfaces, so wall and roof measures may matter far less than the heating does. Our East London and South London area guides go into what this means street by street.

What will not help

  • Draught excluders and secondary curtains — real comfort, no score.
  • Smart thermostats — usually scored the same as a decent programmable one.
  • New appliances — not part of a domestic EPC at all.
  • Low-energy bulbs — a genuine but very small contribution, and most homes already have them.

The evidence point that costs people a band

If the assessor cannot see it, they must assume a default — and defaults are pessimistic. Loft conversions are the classic case: once the roof is a bedroom there is no insulation to inspect. Building control paperwork or the original drawings let the assessor record what is genuinely there. Dig them out before the visit; it is free and it can be worth a band on its own.

If you want to know which of these applies to your home specifically, book online and the report will tell you in order of value.