Damp and mould before an ECO4 survey: what UK households should know (guide 2026)

Guide 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 homes that apply for ECO4 have some damp or mould, often because they are hard to heat. Surveyors need to see it, because insulation should not trap moisture. This guide explains what to look for and what to mention. It is general information from ApplyFreeBoiler.uk, a heating and insulation installer in Bury. Your surveyor will explain what applies to your home. This page does not guarantee funding.

1. Condensation or a leak

Black spots on cold outside walls, window reveals and behind furniture are often condensation. A damp patch that grows after rain, or below a bathroom, is more likely a leak.

2. Tell the surveyor

Point out every damp or mouldy area, including ones behind wardrobes or in the loft. Hiding them can lead to problems later.

3. Some causes come first

Leaking gutters, cracked render, blocked air bricks or a roof leak may need fixing before wall or loft insulation can go in safely.

4. Ventilation matters

Insulation makes a home more airtight. Trickle vents, extractor fans and air bricks help moisture escape, so keep them open and working.

5. Cleaning mould safely

Wipe small areas with a suitable mould cleaner, wear gloves, and keep the room ventilated. Large or returning patches need the cause investigated.

6. Renters

If you rent, report damp and mould to your landlord in writing. Your local council can advise if it is not dealt with.

7. After the work

Warmer walls and steadier heating usually reduce condensation. If damp appears in new places after insulation, contact your installer.

8. Check funding and local figures

See ECO measures by council on ApplyFreeBoiler.uk, built from DESNZ Household Energy Efficiency statistics, to see how many ECO measures have been installed in your local authority area. Use the ApplyFreeBoiler.uk eligibility check to see whether an ECO4 heating or insulation pathway may be available for your home in England, Scotland or Wales. ECO4 is due to close on 31 December 2026.