Cavity Wall Insulation
What it is:
Insulation injected into the gap (“cavity”) between the two layers of brick in most homes built after the 1920s.
How it works:
If your walls were built with a cavity and it’s currently empty, that gap is doing nothing to stop heat escaping. Filling it with insulating material closes that gap.
Key benefits:
- One of the best-value upgrades available, alongside loft insulation
- Minimal disruption - installed from outside through small drill holes, filled afterwards
- Can reduce heating bills noticeably within the first winter
What it costs:
Typically £800–£2,500 for an average semi-detached home, depending on wall area and property type
Is it right for your home?
Only if your walls actually have a cavity – solid-walled homes
(common in properties built before the 1920s) need a different approach (see External or Internal Wall Insulation below). We’ll confirm your wall type at assessment; it’s not always obvious from the outside.