1″ XPS between framing and sheathing – GreenBuildingAdvisor

I happened to see this at a construction site today. One inch XPS directly over the studs, and then sheathing — Zip board — over the XPS.

I thought it was a bit curious. Not an expert on framing, but my understanding is that sheathing has to be directly attached to framing to be prescriptive in terms of meeting shear resistance. I know Zip allows their Zip-R product to be used as structural sheathing with their approved fastener schedule, but I’ve never heard of them allowing another product.

Is this something an engineer would have to sign off the fastener schedule on?

It’s also possible these guys are just winging it, I haven’t been impressed so far with their framing.