Hi Emmett,

The rationale for using polyurethane sheets versus SIPs on the roof are:

1. It costs a fraction of what SIPs cost (atleast around here)
2. It has the same insulation value as a polyurethane SIP (R6-7 per inch)
3. It is a lot lighter than a SIP and therefore can be handled and installed without a crane

Polyurethane sheets are quite common in commercial construction but I wasn't sure if anyone had tried it for residential. In my view, in some applications a SIP on the roof can be a bit overkill. ie: do you really need the 2 sheets of OSB if you have 2x T&G? Metal roofs (quite common in snow country) work fine on non-continuous support (strapping) if the pitch is steep (10:12, 12:12).