Venting question - bungalow on slab with septic system

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Ottawa, Ontario, CANADA
Hi all - I'm building a bungalow on a slab in Ontario, Canada, and although I think I've got the basics of venting and the design, I'm looking for some suggestions on a couple of tricky situations.

I really appreciate any pointers or suggestions this awesome group can provide!

NOTE: Water supply to all points will come up through the bottom of the slab.

I expect that main 4" sewer line running left to right in the diagram to be about 20" below the floor level at the left side - it needs to be this deep for the toilet drain in the Ensuite bathroom to run only vertically through the thickened edge of the slab. For those who might have ideas on how to handle that situation (sewer pipe penetrating the thickened part of slab), the thickened edge is 18" tall and 12" wide, tapering to 6" tall in a 2:1 ratio, 3 ft from the outside edge.

Kitchen: Its a really long run from the kitchen to the main sewer line, and the kitchen sink is located in front of three windows. Other than using an air admittance valve, the only venting solutions I've come up with are:
1) to run the vent horizontal under the kitchen cabinets and then into an exterior wall. I'm reluctant to lose 30% of my insulation space to the vent pipe so I don't like this idea
2) somehow run the vent under the slab - I am not sure how to properly do this - like an island? If I do this, I can run the vent 15' to the nearest interior wall, and then go vertical. this would likely require the vent pipe in the slab to drain away from the kitchen sink, so I was thinking when I get to the interior wall, I would connect the the vent pipe back to the kitchen drain at the junction of the vent pipe in the slab and the vertical pipe, so the vent could drain properly

Ensuite: The home designer has included a 4" furring wall for plumbing along the 'top' exterior wall, so I could probably do a wet vent from the toilet (or toilet and sink) along the 'top' wall and run inside the furring wall and I'd be ok, right? I'm wondering if anyone has any alternate venting solutions that would allow me to get rid of the furring wall and gain 4" of space in the bathroom.

Family Bathroom
This seems fairly straightforward, that the sinks could be vented to the interior wall, and provide a wet vent to the toilet. I do think the shower will have to be vented separately because it is below the toilet (am I right that the toilet should be the lowest fixture when using a wet vent from a sink?)

Principal Bathroom
Due to the depth of the main sewer line at this point (something like 37" below the floor level), I've run the toilet drain next to the inside wall for an easy vent. Can I use this as a wet vent for the shower and sink downstream? Should I just drain the sinks directly into the toilet drain, and provide a common vent in that interior wall?

I might like to orient the septic tank 90 deg to the way its shown in the diagram - in that case I would need to make a 90 deg bend in the septic line right before it goes into the tank - any issue with that?

The other question I have about this system is cleanouts. The only good place to put one near the start of the system is in the utility room. I was thinking I should transition the 2" kitchen drain to 4" sewer line in the utility room, so I could put a 4" cleanout there. This would leave only the Ensuite bathroom without a cleanout.

Sanitary System v1 (1).png


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I might like to orient the septic tank 90 deg to the way its shown in the diagram - in that case I would need to make a 90 deg bend in the septic line right before it goes into the tank - any issue with that?

What kind of septic tank are you installing? Most concrete tanks have inlet (and outlet) ports on more than one side of the tank, (CLICK ON THE ATTACHED DRAWING), which make it possible to orient the tank like you are saying .

I would avoid any 90 degree bends. Do you have a set of rules for a septic systems installation? Generally the State (here in USA) has permitting and inspection guidelines (and RULES actually) for septic system installs.

Are you doing ALL the work yourself or using a contractor? But -- There are lots of different "tanks" so I would shop around for one that best suits the way you want it oriented - BUT again, it must meet the RULES and guidelines of the environmental protection agency or department, or whoever is over your building permits.


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