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Rendered outer leaves 'not suitable for cavity wall insulation'

Individuals have been advised against installing cavity wall insulation in areas where outer surfaces have been rendered.

Writing in response to a Daily Telegraph reader's query, Jeff Howell explained that doing so could cause future problems.

He described how rendered outer leaves can absorb rainwater through pores and cracks, which are then trapped behind the surface.

It was suggested that this type of construction can cause dampness to form in cavity wall insulation as it prevents "drying by evaporation".

"Most dampness with cavity wall insulation is due to moisture generated within the home, which condenses within the filled cavity," Mr Howell stated.

Therefore, he claimed that placing this type of lagging behind rendering will only increase the likelihood of the material becoming waterlogged.

For homes that are not suitable for this installation, the Energy Saving Trust recommends considering solid wall insulation instead.

The body advises that walls that are exposed to driving rain should not be fitted with cavity wall insulation.