This building has blockwork external walls, steel frame structure forming a cavity, and a straw board inner wall finished with Gypsum plaster. It is the cavity that forms a break between the inner and outer walls so when this is filled with insulation, any dampness that penetrates the external wall is able to track across to the inner wall. There was a hairline crack in the external render which allowed rainwater to penetrate. This being a steel framed building, the saturated insulation kept the metal wet enough for it to completely corrode causing severe structural damage.

If you have cavity wall insulation, make sure there are no external defects in roofs, gutters, window/door frames, wall coatings etc. Any rainwater penetration, even through hairline cracks, can cause extensive internal damp related issues, fungal decay (wet/dry rot), and even collapse of building elements.

If in doubt, take it out!

There are many companies now set-up for the removal of cavity wall insulation.