Is this the right way to rehab a flat roof?

[Chris Baxter]

It's time to re-roof one of our MF buildings and I don't have any experience dealing with flat roofs with torch-on membranes.  The surface of the roof is ~5500 ft sq, and the building is in a cold climate (nice summers, snowy winters).  The roofing contractor is proposing that we go over the existing roof with 2ply modified bitumen. If you have any insight as to whether this is a good idea, I would be happy to receive it. Here are the details:

• Clean any loose debris off roof and remove vinyle flashing at roof edge. Dispose of material off site.
  Supply and install mechanical fasteneres 24" o.c. at roof edge perimiter, cover with 13" wide membrane torch applied.
• Supply and install Sopralene Flam Stick base sheet membrane to seal roof edges, come with Elastocol Stick primer.
• Supply and install slope insulation cricket, 1:1 ratio, between roof drains, mechanically fastened.
• Supply and install Soprafix Base 630 base sheet membrane to seal slope insulation cricket, mechanically fastened
• Supply and install standard colour 0.026" (24g) gravel stop metal flashing, come with 6" reinforcement membrane
• Supply and install granules Sopralene Flam 250 GR cap sheet membrane, torch applied.

Thanks!