Russell do you have some sort of drawing as to how you would achieve a slimmer overhang (and fascia) on a warm roof? My current extension roof build up will be 8x2 joist, firring strip, 18mm OSB, VCL, 150mm Celotex, 18mm OSB and finally EPDM with traditional gutters, but im struggling to find a way to reduce the overhang thickness. This is all sitting on block - cavity - block