Getting a 1930s semi-detached house to EPC C

Why this type behaves the way it does

• Cavity walls (often uninsulated in early examples)
• Decent-sized loft
• Frequently extended at the rear

Measures that typically reach C

Cavity wall insulation

Homes built from roughly the 1920s to the 1990s usually have a gap (cavity) between two layers of external wall. Where that cavity is empty, injecting insulation through small holes in the mortar fills it in a day or so, with no internal disruption. For a typical cavity-walled semi it’s one of the most cost-effective steps to a higher band, often paired with loft insulation.

Loft insulation

Topping up loft insulation to the recommended 270mm is usually the cheapest high-impact improvement, because a quarter of a home’s heat can escape through the roof. It’s quick to install in an accessible loft, rarely needs consent, and the SAP uplift per pound spent is among the best of any measure — which is why it’s almost always the first recommendation on an EPC.

A modern condensing boiler

If the boiler is old and non-condensing, replacing it with a modern A-rated condensing model recovers heat that would otherwise go up the flue and runs far more efficiently. It’s a bigger job than the insulation measures, but for a gas-heated home with an ageing boiler it can deliver a solid jump in the rating alongside lower running costs.

Heating controls

A programmer, a room thermostat and thermostatic radiator valves let the heating run only when and where it’s needed, rather than heating the whole home all the time. Adding the controls a system lacks is inexpensive, improves the EPC, and is one of the simplest ways to trim a tenant’s energy bills.

Double glazing

Replacing single-glazed windows with modern double (or secondary) glazing cuts heat loss and draughts and lifts both comfort and the EPC score. In conservation areas or on listed buildings, slim-profile or secondary glazing is often the route that keeps planning happy while still improving performance.

Low-energy lighting

Swapping any remaining halogen or incandescent bulbs for LEDs is the cheapest improvement of all, and it appears on a surprising number of EPCs. It won’t move a property a whole band on its own, but as part of a package it’s an easy, instant win with no installer required.

Cavity wall and loft insulation together often move a 1930s semi several SAP bands for relatively modest cost.

Check your property’s real figures

The above is general to the construction type. Enter a postcode for the actual current band, the gap to C, and the costed measures from that property’s own EPC.

Common questions

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Guidance is general to the construction type and indicative; the cost figures in the checker come from each property’s own EPC. EPC data: contains public sector information licensed under the Open Government Licence v3.0.