This is one point that is am relying on the builder's experience of such situations. The builder has insisted that this is a cracked pipe issue coupled with the truss brackets being "maxed out" which is pulling up the internal walls and door jambs. Although when someone says "I'm 95% sure!" I get a bit jittery. If I was doing it myself and was prepared to bare the costs, I would have done the geotechnical > plumbing inspection etc.