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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.

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Are we talking metal or plastic pipe? –  bib Jul 20 '12 at 23:07
    
I think in most cases, the pipe is actually burried below the slab floor, in the dirt/gravel, not in the floor itself. –  Steven Jul 26 '12 at 13:20
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2 Answers

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 7.3.5.3 Isolation from Loads:

  1. Where piping passes through or under a wall it shall be installed so that the wall does not bear on the pipe.
  2. All pipping shall be installed without undue strains or stresses and provisions shall be made for expansion, contraction and structural movements.
  3. No piping shall be embedded in concrete or masonry.

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 7.3.5.3. 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.

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Thanks! The bathroom is raised to account for the correct level for the greywater diversion. In other words, the gravel underneath the floor is going to be covered with more earth on which the pipe will be encased, and then the earthen floor will be the finish layer (4-8"). I guess from the above response, I can say that the piping is indeed bedded in the gravel/sand of the area below the earthen floor, even though this floor is actually a foot or more above the main floor. (sorry If I'm confusing). We too, encased our main septic drain in a sleeve..we found a fairly sturdy old metal sleeve. –  Sandra Jul 29 '12 at 21:29
    
Our building jurisdiction is very by-the-book. My husband is an engineer so they were happy for him to take responsibility for the main building envelope. In this, the plumbing, they have wanted to be more involved. Before we started the plumbing they decided they would require us to hire a plumber to design the system (even though it is fairly simple). We've managed to convince them otherwise. :) Although everything is to code, the system allows for a greywater system later when the code is more permissable, so the two drains (black and grey) look funny to them. C'est la vie! –  Sandra Jul 29 '12 at 21:36
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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.

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