The walls are covered in two layers of 2 in thick rockwool.
Roxul on roof.
Single ply roof insulation.
An underlayment will be installed over the insulation and overhang and then the metal roof is installed directly on top of the underlayment.
Rockwool multifix is a mineral fiberglass faced stone wool product that can be installed under many single ply membranes.
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.
Single ply roof systems can provide an easy to install seamless roof assembly.
The siding will also secure it.
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.