Does your home have a cavity?
Most houses built after the 1930s have two-leaf walls with a gap between. Brick pattern is the giveaway: all bricks the same length in a row means a cavity; alternating long and short means a solid wall. Homes built after about 1990 usually had the cavity insulated at build. An installer confirms with a borescope.
When it is suitable
- Cavity at least 50mm wide and clear of debris
- Walls in good condition with no cracking or failed pointing
- Not in a severely exposed location with driving rain on unrendered brick
- No existing damp problems
When it is not
Narrow or rubble-filled cavities, exposed unrendered walls in the wet west and north, timber-frame construction, and walls with existing damp. Filling these causes the failures cavity insulation is known for.
Tell us the property and we will show the likely route. Installers on our panel must confirm suitability before quoting.
Cost, guarantee and funding
£700–£2,500 for a typical semi. Work should carry a 25-year CIGA or equivalent guarantee. Cavity wall insulation is a core funded measure under Warm Homes: Local Grant and ECO4 for eligible households. Current routes.
Questions homeowners ask
Does cavity wall insulation cause damp?
Can existing cavity insulation be removed?
- Energy Saving Trust — Roof and loft insulation — checked 2 September 2026
- GOV.UK — Apply for the Warm Homes: Local Grant — checked 2 September 2026
- Ofgem — Energy Company Obligation (ECO4) — checked 2 September 2026