Solid wall insulation under ECO4: UK homeowner checklist 2026

By ApplyFreeBoiler.uk (Reliant Energy Solutions Ltd), a heating and insulation installer in Bury, Greater Manchester. We are not the government, Ofgem or an energy supplier.

Many older UK homes have solid walls rather than a cavity. Solid wall insulation (internal or external) can be an ECO4 measure when the household and property qualify. Use this checklist before you book a survey.

1. Confirm your wall type

Brick pattern, wall thickness and the age of the property help show whether walls are solid or cavity. A surveyor will confirm on site; do not assume from photos alone.

2. Check your EPC baseline

Look up your address on the official EPC register. Solid wall insulation is usually considered alongside the wider ECO4 design, so keep the certificate number and current rating ready.

3. Weigh internal vs external options

External wall insulation changes the outer finish and may need planning checks in conservation areas. Internal insulation reduces room size slightly and needs careful detailing around windows, sockets and floors to limit condensation risk.

4. Note damp, vents and services

Existing damp, blocked vents or poorly detailed services can affect suitability. Flag any history of mould or penetrating damp early so the survey can address it.

5. Compare local delivery data

DESNZ publishes how many ECO measures each council area has received. See ECO measures by council on ApplyFreeBoiler.uk.

6. Avoid fees just to apply

You should not pay a fee only to check ECO4 eligibility. Use the ApplyFreeBoiler.uk eligibility check to see whether a free boiler or insulation pathway may be available across England, Scotland and Wales.