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Ian McChesney

Re Phil’s query. I’m not sure that the mould issues are tied to a single cause. The ceiling re-insulation will have reduced heat loss into the roof cavity and lowered the temperature of the cavity on cold nights. This may be causing greater condensation on the inner surface of an unlined metal roof. It may be dripping and wetting insulation in certain areas, and getting through to the ceiling gib….but, it seems a bit unlikely I think. For mould on an insulated ceiling I would most likely suspect lack of internal ventilation, particularly if they are 70s houses with aluminium window frames.
On external walls I have observed mould/moss growth on external 60s/70s walls on a few houses – they seemed to share the common characteristics of being shady walls and summerhill stone/ concrete block. This makes me suspect water absorption – maybe through breakdown of some of the mortar and into the surface pores of ageing concrete, and just creating a bit of a breeding ground.