The best measures for EPC D to C, ranked

Not all SAP points cost the same. The cheapest point on this list costs about £25; the dearest costs over £2,000. Here is every common measure in points-per-pound order, with the conditions under which each one earns — or fails to earn — its keep.

1. Hot water cylinder jacket — £25–£50, 1–2 points

If you have a hot water cylinder with less than 80mm of insulation, an off-the-shelf jacket is the single best value item in the entire SAP model. It is a ten-minute DIY job. Homes on combi boilers have no cylinder, so this row simply does not apply — which is why your EPC recommendation list, not this page, should be your starting checklist.

2. Low-energy lighting — £100–£250, 1–2 points

RdSAP records the percentage of fixed lighting outlets with low-energy lamps. Replacing every remaining halogen and incandescent with LED takes the figure to 100% and typically adds one to two points. It also cuts the lighting line of the running-cost estimate on the certificate itself.

3. Heating controls — £350–£600, 2–4 points

A gas-heated home scores better with a full control set: programmer, room thermostat and thermostatic radiator valves (TRVs). Many D-rated homes are missing the room thermostat — a surprisingly common gap in 1970s–90s installations — and adding one is often the cheapest multi-point gain available. A plumber can usually fit a wireless stat and TRVs in a half day.

4. Loft insulation top-up — £400–£700, 1–3 points

Topping up from 100mm to 300mm of mineral wool earns one to three points on a typical semi. If the loft currently has 50mm or less, gains are larger and the job is even more clearly worthwhile. Boarded lofts cost more because boards must be lifted or raised on stilts. Keep photographs taken during the work — once the loft is re-boarded, the assessor cannot see the new depth, and under RdSAP 10 unevidenced insulation may be recorded at its old value.

5. Cavity wall insulation — £1,000–£2,600, 5–10 points

The heavyweight. Walls are the largest heat-loss surface in most homes, and filling an empty cavity moves the wall U-value enough to add five to ten points — frequently the whole D-to-C gap on its own. Suitability matters: the cavity must be at least 50mm, the walls in fair condition, and exposed coastal sites need specialist assessment to avoid driven-rain problems. Use an installer offering a CIGA or equivalent 25-year guarantee, and keep the certificate: it is exactly the evidence the next assessor will ask for.

6. Replacement condensing boiler — £2,500–£4,000, 5–12 points

The most misunderstood measure on the list. Swapping an old non-condensing boiler (typically pre-2005, efficiency in the 65–75% range) for a modern condensing model adds five to twelve points. Swapping a condensing boiler for a newer condensing boiler adds almost nothing — the SAP efficiency figure barely moves. Check the "main heating" efficiency on your current certificate first. If it already says 88% or better, spend the money elsewhere on this list.

7. Solar PV — £5,000–£7,000, 8–14 points

A 3.5–4 kWp array is the largest single point gain most homes can buy. It suits homes that are already insulated but still short of 69 — common with detached properties — and it is the one measure that also generates export income. South, east or west-facing roofs all work; heavily shaded roofs do not — a proper roof survey from installers and consultants like Carbon Legacy settles that question before any money moves. 0% VAT applies to residential installations until 31 March 2027. Panels are a points sledgehammer: do not buy them to close a 2-point gap that £400 of controls would cover.

8. Solid wall insulation — £8,000–£15,000+, 10–18 points

For pre-1920s solid-brick homes, wall insulation (external render systems or internal boards) is transformative on paper but expensive and disruptive in practice. It is usually the only route to C for a solid-walled house starting in the mid-50s, which is why period terraces need a different plan from cavity-walled stock. Internal insulation costs less per room but eats floor space and requires careful moisture detailing — budget for a competent retrofit installer, not the cheapest quote.

9. Double glazing — £5,000–£9,000, 2–5 points

Worth doing for comfort, noise and window replacement cycles; rarely worth doing for the EPC alone. Windows are a small share of total heat loss in the SAP model, so the points-per-pound ratio is the worst on this page. If your home is already double glazed — even with early-1990s units — further glazing upgrades earn close to nothing.

What about heat pumps?

An air source heat pump can score well — recent SAP electricity price factors treat heat pumps far more favourably than older versions did — and the £7,500 Boiler Upgrade Scheme grant changes the economics materially. But outcomes vary with the tariff assumptions and the property, and a heat pump in a poorly insulated home can disappoint on both bills and score. Treat it as a heating decision first and an EPC decision second; insulate before you electrify.

Reading the list against your own certificate

The recommendation table on your EPC already names the measures the assessor judged applicable, each with an indicative cost band and the rating after improvement. Cross-reference it with the ranking above, count the points you need using the SAP points guide, and price the route with the cost ladder. Then keep every receipt for the reassessment.