I’m building a single-storey, pitched roof extension which includes a vaulted ceiling (9” deep trusses).
Building inspector said I can put 8” thick mineral wool roll between the rafters on the sloping part of the vaulted ceiling, leaving a 1” gap for air flow between the top of the insulation and the tiles. I presume that this air gap will allow air flow from soffits upwards to the ridge, preventing condensation build up.
However, my builder has expressed concern, stating this is a mistake as 1” is insufficient airflow. He has suggested that I do away with the mineral wool roll and buy Kingspan boards (at 4 times the cost!!).
I just wondered if anyone out there can offer any advice?
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