Also should I be leaving an air gap between the insulation and the existing ceiling/roof?
Not just an air gap, but a ventilated one - irc, 50mm is recommended.
You could put air vents into the roof itself, i guess.
I’ll leave 50mm. To be fair the whole thing is pretty breezy, hence adding some insulation…
@Sam_w started
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Not just an air gap, but a ventilated one - irc, 50mm is recommended.
You could put air vents into the roof itself, i guess.