Basement bathroom rough-in prelim layout

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Horst22

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Hello everyone,
As many others, long time reader, first time poster. I'm planning a basement bathroom and would appreciate some advice on an initial layout of the rough-in. I live in Iowa; code is 2021 UPC.

I have done some light plumbing work, but not a project like this (I apologize if my terminology isn't up to par). Have tried to read through some code and forums like this (very helpful) but would appreciate some advice on my initial layout or if there is a better approach. Once I have this, then I'll need to work through fittings to use/etc.

The attached picture has a rough outline of what I was thinking. I still need to get exact locations/framing/move existing doorway but want to plan where I'll have to cut through the slab. We have existing sewer lines below the basement floor and won't need an ejector pit. The nearest point to tie in is below the bottom of the picture, about 9' from where toilet/shower drains meet. From my understanding, the toilet/shower share a wet vent and has to be within 6' of the toilet and 8' from the shower trap (will be about 4-5' and 6' as drawn). I think this is too far for the sink so I was planning an individual vent for the sink. I'm planning to tie into an existing washing machine vent on the floor above.

Any other advice/suggestions would be appreciated.
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wwhitney

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A couple comments:

- No horizontal dry vents under the slab. But perhaps your drawing means that you'll have a vertical dry vent rising in the wall depicted by the 2x4, and it will connect over in the ceiling joists?

- The lav can wet vent both the shower and the WC. To do that you use a 2x2x1-1/2" san-tee for the lav vent/drain connection to the trap arm, and run the 2" lav drain to pick up the shower drain first, then to a 3x3x2 wye to pick up the WC drain (or a 3x2x3 wye, which doesn't exist as a single fitting).

- In the wet vent arrangement, the various length limits are: 42" for the lav trap arm (from trap under the sink to the san-tee) if you use a 1-1/2" trap; 60" for the 2" shower trap arm (from the trap to the wye where it joins the lav drain that wet vents it); and 72" for the WC fixture drain (from the closet flange along the pipe to the wye where it joins the lav/shower drain that wet vents it).

Cheers, Wayne
 

Horst22

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Thank you, this is very helpful.

- That was a horizontal dry vent - I will remove that.

- I think I am confusing the limits for trap arm length with the total distance from trap to dry vent and why I had that extra vent line there. To confirm my understanding - If I remove what I had for shower/WC vent and instead wet vent off of lav; my trap arm for the WC would only be from WC flange to the drain line or about 3.5' in this case. Trap arm for the shower would be about 1' or so. These would be be within length limits. The actual wet vent starts where directly below dry vent and ends at the wye where the WC trap arm joins.

-Assuming this is what you meant and is up to code; would it be better to add individual vent for WC up the wall and through floor joists? Or since wet vent is up to code, I'm no better off with individual WC vent.
 

wwhitney

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Yes, the trap arm ends at the wet vent, not at the dry vent. The wet vent length is not limited.

As to the last question, no opinion; I'm familiar with what the code says and allows, but not with actual performance. Some people certainly think dry venting is better than wet venting, but whether that is based on data or just on tradition, I don't know.

Cheers, Wayne
 

John Gayewski

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Yes, the trap arm ends at the wet vent, not at the dry vent. The wet vent length is not limited.

As to the last question, no opinion; I'm familiar with what the code says and allows, but not with actual performance. Some people certainly think dry venting is better than wet venting, but whether that is based on data or just on tradition, I don't know.

Cheers, Wayne
We here in Iowa are upc but have our own trap length limits. 6' for 1.5" pipe and 8' for 2"
 
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