Flat Roofing - Cover Board/Fiber Board/Insulation Cover Board

Hi BP, does anyone have experience with flat roofing? I have a contractor that wants to install what seems to be a cover board over the bare wood decking of the roof, then the glass base sheet, then the torchdown roofing. I was under the impression insulation should be installed somewhere in the mix if not first ten everything else. Anyone know if his approach is acceptable?