A MgO SIP house went up near here. Looks to be primarily light steel construction with the MgO sips as infill. I got a sample and soaking it in water had no effect. The roof is not made of SIPs and I assume that they will insulate it in some other way. I can't say that I understand using 5"
of foam and then having so much thermal bridging. The SIPs will be covered with mesh + stucco/plaster.