I never claimed to be an expert. I have built a lot of houses, worked as a building inspector and a licensed energy auditor and developed the concept with a code official friend. We did work with a structural engineer on this. He vetted what I did and signed off on it for the code people who asked for an engineer's stamp. Gable end walls can either be built as taller panels since we are usually laminating layers of foam together or they can be stacked, much the way a stick built wall might be.

There are studs in these walls but the foam is contiguous. The studs or wood framing are installed on both faces and do not penetrate the foam. The fasteners do penetrate. Are they a big thermal bridge? No.

The panel is structural. It is insulated and it is a panel. Is it a SIP? I would consider it one.

This is solely offered as an interesting DIY project. I would advise anyone considering this should not jump in and do a house this way without building a small shed to try out the concept. That is what we did.
We have had people who built their own homes without a trial run.

There are a lot of variations on the theme. They are a lot of ways to do it wrong, but I think some simple understanding of the concept of how a panel works and how a stick built wall structure works helps a lot.

I don't want to get into a flame session about this since I believe SIPs manufacturers offer a lot of value for the money. The question was asked and this is something we have been doing this for a while.

The use of building paper can be optional. We used 30# felt when we did it. Some people used house wrap. If you are not filling the space in between the exterior wood, a wrap or paper will not be very effective since there is a large air space. The building is not going to be any tighter with a wrap.

BTW, I neglected to mention that sealing in between the panels is, of course, very critical. And the way we did it was a little crude, just foaming in between the panels. You can shiplap the panels if you want. We did not do that since it seemed like a lot of hassle.
Like I said, there are a lot of options for doing this.
Tom