Size of Air Gap on Pitched Roof for Single Storey Extension Information, help and tips on many areas of roofing including trusses, tiling, venting, insulation etc....

[lesrico]

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?

Thanks in advance.

Lee.

[michaelscad]

50mm minimum ar gap between insul. and tiles