Shower drain venting

[jeromio]

I'm laying out a new bathroom with vanity, toilet and shower. For the shower drain vent, I was planning to run it "backwards" to join the vents for the sink and toilet. However, there is a new wall that runs "ahead" (forwards) of the drain and I *could* add a vent there. It's more pipe and a bit more effort, but maybe works slightly better? So my question is, should I go ahead and run all the vents together in the back wall of the bathroom, or run this extra vent in this forward wall for the shower (and tie them all together in the attic)? The bathroom is a total 5ft wide, shower drain is center, so 2.5ft, but it angles towards that toilet drain, so the forward wall (a closet wall) will be slightly closer than the back wall. So, less below floor horizontal distance.

Note my CAD skills are ick and I realize that toilet 4-3 bend looks like a trumpet.
Thanks in advance.

 

[wwhitney]

So, the NC plumbing code is based on the IPC, and the IPC in 905.4 basically prohibits a horizontal vent below the floor. NC has amended that section to add the exception "When vents for interceptors and isolated floor drains are not located near an adjacent wall, the vent must rise 6 inches (152 mm) vertically before turning horizontally and continuing to the nearest wall. For cleaning purposes, a cleanout the same size as the vent shall be installed."

https://up.codes/viewer/north_carolina/ipc-2015/chapter/9/vents#905.4

I'm not sure if a shower drain would qualify as an "isolated floor drain". The standard solution is just to omit the shower dry vent and rely on horizontal wet venting via the lav. Just like the WC relies on horizontal wet venting.

Cheers, Wayne

 

[Sponsor]

 

[Terry]

The lav wet vents the shower and the toilet.

 

[jeromio]

Ok - thanks for the diagram.

 

[jeromio]

Just to clarify: the wet potion of the vertical wall pipe must be 2in, but the dry vent, above the T to the sink drain - that will be 1.5in

 

[Terry]

If you are venting the toilet, shower and lav, the vent remains 2" under UPC
It may be that the dry portion of the vent can be 1.5 under IPC

 

[wwhitney]

UPC (where Terry and I live) requires a minimum 2" vent for a WC, and a minimum of 2" for any wet vent.

IPC allows a 1.5" dry vent for a 3" drain, and it allows 1.5" for wet vents carrying only 1 DFU (just 1 lav). So in Terry's drawing, under the IPC, the vent and the lav drain up until it hits the shower can both be 1.5".

Cheers, Wayne