Foam

The white material is 3" thick expanded polystyrene. Over that, we're putting on a breathable, water resistant membrane by Vaproshield, taping the joints to maintain our air tight envelope. Then, wood furring strips to attach the siding to.

Shell

I've finally made some decisions regarding the siding. I'm planning to use flat sheets of corten weathering steel. The following picture shows what it will look like once it's weathered:

So we're installing felt paper on the plywood followed by 3" of Expanded Polystyrene Rigid Foam insulation, then covering the foam with wrapshield by Vaproshield. The steel siding will be installed on wood furring strips, creating a rainscreen. The wrapshield will act as a breathable water resistant membrane.

The above picture shows the double 2x4 frames around the window openings, which will be flush with the foam, for the siding attachment.