We are building an earthship and our bathrooms will feed a greywater system. We've spec'd the usual 1 1/2 drain for the tub...but we plan to bury it in an earthen floor in the bathroom (our code treats this floor as though it was a concrete slab). We read somewhere (of course can't remember where ) that the minimum size that can be buried in concrete is 2" pipe...do we need to upsize our drain sizes? We are in Canada.
I'm not aware of any restrictions on the minimum size of a drain pipe encased in concrete in either the BC or National plumbing codes.
If the floor is truly classified as concrete, there may be issues on how literal the inspector's interpretation of the code is.
The 1998 BC Plumbing code included the following:
Section 7.3.5 Protection of Piping, Subsection 188.8.131.52 Isolation from Loads:
The BC building inspectors issued interpretation 98-0056 regarding this issue. The bottom line was that pipes embedded in concrete needed to be sleeved. However, the current BC plumbing code (2006) has removed both sentience 2 and 3 from 184.108.40.206. The national code (2005) also reflects this change. (The BC Plumbing code is almost an exact copy of the national code).
The short answer is that it comes down the the inspector's opinion. It would probably be beneficial to contact your local inspector to discuss.
When we poured the footers for our foundation, we laid a paint can on its side, opened on both ends and extending out through the forms, in the spot where the septic drain pipe would pass out of the house, so the wall above won't rest directly on the pipe - there's a metal-sleeved tunnel through the footer. I imagine you can do similar with earth-ship walls, though check local codes to be sure.