Newbie DIY a very simple toilet and tub in slab, help

[Rensho]

I'm building a qounset hut home and we're about to pour our slab in 10 days.
I have laid out the 1bd/ba to use a short and simple bathroom layout next to the exterior wall.

I'm running the toilet to a 4" drain, which the tub 2" drain would WYE into within the 2 feet of the toilet, the 4" drain then heads 2 feet to a 4" vertical vent stack, as well as head out of the house to a septic tank 8 ft away.
I am assuming i can drain and vent the tub into the 4" drain and the stack would serve as a vent as it is within ~5ft from tub trap.
One limitation I have is the room under the slab is limited to 12", as the 4" pipe needs to run out of the building and go into the septic at/near that elevation.

Would someone critique and help verify the fittings I need?
I've attached my chicken scratch drawing as well as the real life lines on the actual gravel pad.

Beyond the slab rough in, i hope to wet vent bathroom and kitchen sinks and a washer into the 4" stack.

Thank you for your consideration and help.

 

[Rensho]

Would any one of the 100s of knowledgable people in here spend 1 minute to give me guidance? Thanks so much.

 

[Sponsor]

 

[Reach4]

The tub drain line has to be vented, I think with 2 inch, before the tub drainage joins the toilet drainage.

I was going to say you were no Picasso, but have re-thought that.

 

[Rensho]

The tub drain line has to be vented, I think with 2 inch, before the tub drainage joins the toilet drainage.

I was going to say you were no Picasso, but have re-thought that.

Thanks for the reply. So the main stack vent within ~5ft of the tub trap will not count as a valid vent?
Agreed, my chicken scratches are terrible.

 

[wwhitney]

Question: what other drainage and vents through the roof does this quonset house have besides the tub and WC?

It appears Washoe County, NV has adopted the UPC per https://www.washoecounty.gov/building/building_codes.php so my comments are based on the UPC.

Then the WC needs a minimum 2" vent which must be connected within 6' of pipe run (vertical and horizontal) from the closet flange. It also needs to connect before or as the WC drainage joins the tub drainage. There is also a requirement in the UPC that the total vent area through the roof meet or exceed that of a single 3" dry vent. The WC drain could be 3" rather than 4", but 4" is also fine. There may be a need to use a 4" building sewer rather than a 3", not sure about that. The building sewer starts a foot or two (I forget the exact distance) after the drain leaves the footprint of the building.

So, if you have elsewhere a vent through the roof which is at least 3", or have at least a 2" plus a 1-1/2", then your dry vent for this area only need to be 2". If you are relying on this vent through the roof to satisfy the UPC's aggregate vent area requirement, it would need to be 3" and connect to a minimum 3" drain.

With all that said, your options are:

A) Pull separate dry vents off the tub fixture drain and the WC fixture drain, both upstream of the wye where the two drains join. In this case the tub dry vent could be 1-1/2", and the WC dry vent could be 2" or 3" depending on the strategy for compliance with the aggregate vent area requirement. These dry vents come off the top of the drain and rise vertically through the slab (vertically includes up to 45 degrees off plumb), within the foot print of a wall the drain is crossing under.

B) Pull only a dry vent off the tub fixture drain, and use the tub to wet vent the WC. This dry vent would have to be at least 2", as would the tub drain downstream of the vent takeoff. [Upstream of the vent takeoff the tub drain should match the trap size, which is allowed to be 1-1/2", although I like 2" better.] But if you want to use a 3" vent to satisfy the aggregate vent area requirement, then you'd need a 3" drain downstream of the vent takeoff.

Note that the trap arm is the drain between the trap and the vent for the trap, which is either the dry vent takeoff, or the wye where the fixture drain joins another drain that is wet venting it. For the UPC, the trap arm is limited to 42" in length and 1-1/2" of total fall for a 1-1/2" trap; and 60" in length and 2" of total fall for a 2" trap. And as noted, for a WC, which does not have an external trap, the constraint is instead 72" of fixture drain between the closet flange and the vent connection.

Cheers, Wayne

 

[Rensho]

Question: what other drainage and vents through the roof does this quonset house have besides the tub and WC?

It appears Washoe County, NV has adopted the UPC per https://www.washoecounty.gov/building/building_codes.php so my comments are based on the UPC.

Then the WC needs a minimum 2" vent which must be connected within 6' of pipe run (vertical and horizontal) from the closet flange. It also needs to connect before or as the WC drainage joins the tub drainage. There is also a requirement in the UPC that the total vent area through the roof meet or exceed that of a single 3" dry vent. The WC drain could be 3" rather than 4", but 4" is also fine. There may be a need to use a 4" building sewer rather than a 3", not sure about that. The building sewer starts a foot or two (I forget the exact distance) after the drain leaves the footprint of the building.

So, if you have elsewhere a vent through the roof which is at least 3", or have at least a 2" plus a 1-1/2", then your dry vent for this area only need to be 2". If you are relying on this vent through the roof to satisfy the UPC's aggregate vent area requirement, it would need to be 3" and connect to a minimum 3" drain.

With all that said, your options are:

A) Pull separate dry vents off the tub fixture drain and the WC fixture drain, both upstream of the wye where the two drains join. In this case the tub dry vent could be 1-1/2", and the WC dry vent could be 2" or 3" depending on the strategy for compliance with the aggregate vent area requirement. These dry vents come off the top of the drain and rise vertically through the slab (vertically includes up to 45 degrees off plumb), within the foot print of a wall the drain is crossing under.

B) Pull only a dry vent off the tub fixture drain, and use the tub to wet vent the WC. This dry vent would have to be at least 2", as would the tub drain downstream of the vent takeoff. [Upstream of the vent takeoff the tub drain should match the trap size, which is allowed to be 1-1/2", although I like 2" better.] But if you want to use a 3" vent to satisfy the aggregate vent area requirement, then you'd need a 3" drain downstream of the vent takeoff.

Note that the trap arm is the drain between the trap and the vent for the trap, which is either the dry vent takeoff, or the wye where the fixture drain joins another drain that is wet venting it. For the UPC, the trap arm is limited to 42" in length and 1-1/2" of total fall for a 1-1/2" trap; and 60" in length and 2" of total fall for a 2" trap. And as noted, for a WC, which does not have an external trap, the constraint is instead 72" of fixture drain between the closet flange and the vent connection.

Cheers, Wayne

Wayne, you're very kind with your knowledge and time. I'll do my best to digest what you wrote. At this time, i'm thinking option B and I'll pull the vent up the tub plumbing wall for shower head and dive the vent into my main 4" stack.
The main reason why i'm wanting a 4" vent stack is I may at a later date add a bathroom on floor above. I want to leave that as an option to drain the 2nd story bath into this main 4" stack and then out the building into the septic tank 6' away.

 

[wwhitney]

The main reason why i'm wanting a 4" vent stack is I may at a later date add a bathroom on floor above. I want to leave that as an option to drain the 2nd story bath into this main 4" stack and then out the building into the septic tank 6' away.

Note that if you use the 4" stack for drainage from a floor above, it may no longer be a vent stack for this floor. So if you want this option, plan on separate drainage and vent stacks.

Cheers, Wayne