Good morning.
I have a sloping roof on an extension, ready for me to put in the insulation and plasterboard. I plan to use Celotex or Kingspan between the rafters. (Thanks to those who advised me on that here, a few weeks ago.)
There is a continuous strip of ventilation along the eaves, and two chimney-type vents further up, one for each room in the extension. (Are these called tile vents?) The roof space is divided by a wall also, so there is a space and a "chimney" vent above each room, but no air flow between the rooms in the roof space.
When I insert the insulation boards, leaving the statutory
50 mm gap below the sarking, air (and moisture) will be able to move along the spaces (i.e. parallel to the rafters) and through the breathable sarking and roof. Then each chimney-vent will only be connected to one inter-rafter space. This seems a bit odd to me. If those vents are required, should they not each vent a large area of roof space? Otherwise, what is the point of them?
Or is there sufficient across-the-rafters air flow in the little space between the rafters and the tiles?
And another thing: assuming this is all OK for ventilation, can I put lighting junction boxes in the
50 mm gap?
Thanks for any advice.
-David Pearson (a bit groggy in Taunton)