Yes, but not *that* significant.
I would definitely do it between. My choice would be at the top and taped over, BUT if you want the void, simply go around each 'valley ' with a mastic gun or decorators caulk after fitting to ensure its all air tight.
Yes, I want the void above - wiring and central heating pipework run in it. And although I've been advised by the Management that under floor heating isn't happening now, I want the option to do it in the future.
Cheers Richard
I think it would probably hold by means of 75mm Pb screws diagonally downwards, while the foam cured.
I have a cunning plan to ensure continuity of insulation beneath the joists, which I will share with you if it works, this weekend.
Cheers richard
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