PVC SDR35 versus PVC SCH40

I can tell from reading specs how these two pipe types differ. My question is about usage.

The pic shows the plan view of the underslab waste and soil drains in a house being built. The line exits the house at the bottom of the drawing, and heads for the septic tank.

The main spine of the underslab spider is 4" at the suggestion of our plumber. Because the branch fittings are SCH40 PVC, the majority of the line under the slab needs to be SCH40 PVC.

My question is, where can we transition from SCH40 to SDR35? We fall under the IPC, and the limited code refs I have do not clarify this for me.

About 5 or 10 foot outside the footing.

Pvc

Outside the building, but, I personally, would not transition to the thin wall pipe. It can only cause problems down the road. Stay with sch. 40, even though it costs a few cents more.

And sleeve it going through the foundation or wall unless it is completely under the footer,