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EPC D → C upgrade for Cavity-uninsulated semi
Uninsulated cavity walls are the single highest-ROI fix in the UK housing stock — £1,200 for 6 SAP points. This archetype gets to EPC C fastest.
Upgrade measure stack
Cheapest-first ordering — calculator stops adding measures once the gap to C closes.
| Measure | Cost | SAP uplift |
|---|---|---|
| Full LED lighting retrofit | £250 | +1.0 |
| Thermostatic radiator valves + controls | £400 | +1.0 |
| Cavity wall insulation | £1200 | +6.0 |
| Air-source heat pump (BUS-eligible) | £11000 | +10.0 |
| Total | £12850 | to band C |
What's specific about this archetype
Most homes built 1920–1980 have cavity walls suitable for bonded-bead or fibre fill. The install takes half a day, is grant-eligible for many households via GBIS or ECO4, and typically delivers £150–£400 a year in bill savings on top of the SAP uplift. Always confirm the cavity is dry, unfilled and wide enough (50 mm+) before booking.
Model your exact property
The figures above use a reference archetype. Your real floor area, mortgage balance, current energy bill and exact current band will shift the numbers. Use the full EPC upgrade calculator for a customised version, the insulation savings calculator to choose between competing fabric measures, and BUS grant eligibility if a heat pump is on the shortlist.
Other wall-type archetypes
| Archetype | Start → Target | Net cost | Annual saving |
|---|---|---|---|
| Solid-wall terrace | EPC E → C | £22650 | £322/yr |
| Cavity-uninsulated semi (this page) | EPC D → C | £5350 | £171/yr |
| Timber-frame home | EPC C → B | £4150 | £90/yr |