On Mar 10, 6:14*pm, John Rumm wrote:
Regarding insulation, you need to decide if you are going for a warm or
a cold deck roof. With a felted roof, warm deck[1] is quite easy these
days. Lay rigid PIR foam boards on the firings, and then ply screwed
down through the insulation, then felt etc on that. With corrugated
sheet that may or may not work as well.

John, I am going to install a warm deck on my garage. I was advised to
lay a sheet of 9mm ply below the celotex. This prevents them squishing
on the timber when you screw down the top decking. Also I was trying
to work out how to apply foil tape on the bottom of the boards - in
order to maintain the vapour barrier on the bottom side of the
insulation. Obviously you can't hinge the joints down and at a width
of 7 metres, trying to lift up an entire row could be tricky.

Im laying a deck with 18mm 8ft x 2ft T&G spruce ply. I am hoping that
will give a stronger deck than butt jointed ply.

Dave.