Cavity wall insulation
If your walls were built with a gap between two skins of brick, filling it is one of the biggest single savings on heat loss — and a strong step towards EPC C.
What it is
Most homes built from the 1930s to the early 2000s have a cavity — a gap of around 50mm between an outer and inner wall. We inject an approved bonded-bead or mineral-wool product through small, neatly made holes in the mortar, filling the cavity so it stops convecting heat out. The holes are made good to match your brickwork.
Why it matters for 2030
Uninsulated walls are the largest single route for heat to leave a typical house — more than the roof. Filling the cavity is therefore one of the highest-impact fabric measures for both the EPC score and the tenant's bills, and it is far cheaper and less disruptive than insulating solid walls. It is a fabric-first measure, exactly what the new standard wants done before heating or generation.
Which homes suit it
Cavity-built properties in reasonable condition with a clear, dry cavity. We survey first with a borescope: homes exposed to driving rain, with rubble-filled cavities, or with existing damp are screened out or remediated before any fill, because bad cavity fill causes damp. Solid-wall homes (typically pre-1930 brick or stone) need internal or external wall insulation instead.
Grants that apply
Covered by the Warm Homes: Local Grant for eligible tenants and by ECO4 until it closes on 31 December 2026, and zero-rated for VAT until 31 March 2027. Grant funding counts towards your £10,000 cost cap. We confirm eligibility on the grants page before quoting.
How we do it
PAS 2035-coordinated, installed to PAS 2030 by our accredited partner LAMTANS Engineering, lodged with TrustMark, and backed by an insurance-backed guarantee (typically 25 years through CIGA or equivalent). Fixed price from our own book, and part of the whole-property plan from your free assessment.
Common questions
How do I know if my walls have a cavity?
Homes built from the 1930s onwards usually do; we confirm with a borescope check before quoting.
Is it messy or disruptive?
No. It is injected through small holes in the outside mortar in a few hours, and the holes are made good to match.
Can cavity insulation cause damp?
Only if the wall is exposed to driving rain or already has defects; our PAS 2035 survey rules those out before any work.
Is it grant-funded?
Yes, it is an eligible measure under the Warm Homes: Local Grant and ECO4, and zero-rated for VAT until 31 March 2027.
How much will it save?
Cavity walls are one of the biggest heat-loss routes, so it is among the highest-saving measures for a typical semi.
Related: external wall insulation · internal wall insulation · loft insulation