The more extended answer is that while this approach is fairly common on flat commercial roofs especially in europe it is almost never done on sloped roofs especially in north america.
Roxul on roof.
Known as comfortboard is this insulation has impressed us with its green virtues versatility and price.
The brief answer is that you can substitute semi rigid mineral wool panels for rigid foam in any roof assembly that requires rigid foam.
A few washer nails hold the comfortboard in place.
Made in canada by roxul comfortboard is one product in a line of stone wool products that combine the power of rock with the characteristics of insulation wool.
The walls are covered in two layers of 2 in thick rockwool.
The siding will also secure it.
Single ply roof insulation.
The insulation planes with the roof overhang on the left.