Insulating a 1930s semi-detached house
Inter-war semis are everywhere in the Midlands — and they have specific insulation needs. Here's what works.
The classic 1930s semi is one of the most common house types across Birmingham, Solihull and the wider Midlands. They're solid homes, but they were built before modern insulation standards — so most lose heat through the roof and walls.
The loft
Many 1930s semis have shallow or no loft insulation. Topping up to 270mm is usually the single biggest win, and these lofts are typically straightforward to access and insulate.
The walls
Most 1930s semis have cavity walls — two skins with a gap. If that cavity is unfilled, cavity wall insulation tackles up to a third of heat loss. We survey to confirm the cavity is suitable first.
The 1930s semi sweet spot
Loft insulation plus cavity wall insulation together transform an inter-war semi's warmth and bills — and both are relatively quick, clean jobs.
Don't forget the floors and draughts
Beyond the loft and walls, many 1930s semis have suspended timber ground floors with gaps that let cold air up, and original windows and doors that leak heat. Draught-proofing these is cheap and makes an immediate difference to comfort. If you're tackling the big items, it's worth doing the small ones at the same time.
A sensible order of works
- Loft insulation first — biggest, cheapest win.
- Cavity wall insulation next, if the cavity's suitable.
- Draught-proofing and an efficient boiler to finish.