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Ian McChesney

The house characteristics Phil describes, (and Gleb’s photos), has me thinking about the effect of the thick ceiling insulation in these kinds of low roof-pitch houses. I wonder whether the insulation installed right out to the edge of the roof is actually cutting off what might have been some natural ventilation flows into/out of the roof cavity. For instance, air flow from the wall cavities is now largely cut off (from vent holes in the bricks for those with concrete floor, and from the underfloor space for suspended floor (and Phil says the floors are covered so the air should be dry)), as is air flow from any ventilation holes in the soffit (some houses have them), and from the gaps between the bottom of the corrugated iron and the outer roof purlin. If the insulation substantially reduces air flow from below and from the side, and tightly fitting long-run iron from above is also reasonably airtight (compared with older roofs and tiles), have we created a fairly airtight little high-humidity roof cavity space in which moisture is largely retained and goes through cycles of condensation-evaporation during night and day? And any extract fan venting moisture into the roof space would exacerbate the problem. I don’t know….any other thoughts?