Tens of thousands of homes across Wales have had insulation ‘retrofitted’ in the last decade as part of a government-led drive to cut energy use.

Building Research Establishment (BRE) divided the UK into its driest and wettest areas known as Exposure Zones in its report to the Welsh Government. Most of Wales is in the wettest area - Exposure Zone 4.

A Pontypridd resident had CWI installed for ‘free’ seven years ago. A year later, cracks began to appear in the brickwork and things began "deteriorating" in the house with damp, mould and peeling wallpaper. Although the Cavity Insulation Guarantee Agency (CIGA) said his guarantee was for 25 years, five surveyors who came to view the property all gave him a different reason for the problems.

Another resident had CWI installed in 2004, there were voids in the insulation which were causing cold spots on walls, which led to condensation, damp and mould. He complained to CIGA for three years. Finally in 2016, CIGA agreed the CWI was to blame - and said they would cover the cost of removal - but would not pay for repairs to the house.

BRE warns of the problems installing cavity wall insulation in Zone 4 because of the increased risk of rain penetration if a cavity is ‘fully filled’ with insulation. Unless it is done properly, rain can penetrate the outer wall and get the insulation wet.

It then transfers moisture to the internal walls causing damp problems.

CIGA was set up to help resolve problems and compensate homeowners affected by careless installations. A spokesman said it was a "reliable product" but that "on the rare occasions things do go wrong" "In the vast majority of cases, any issues are fixed swiftly and at no cost to the customer" adding it offers an independent dispute resolution service for any customers unhappy with the result of their case.