Venting and draining help

[T Tran]

Hi everyone. I'm new to the forum and is somewhat new to plumbing. I have done a couple of small plumbing jobs, but this new one will be my biggest ever. Just to give you a quick background. I have a 1 story home that's built on top of a crawlspace. The crawlspace is about 2 feet in height.

I need help with building an additional bathroom and all of its plumbing. Attached is the pic (not the best drawing and not to scale). I have read a lot about drainage and venting lately and came up with the design. The house has a lot of vents that come through the roof. On the drawing, there are a total of 4 vents that come through the roof. Seems like some of the fixtures have their own vent.

The area in green highlight is kinda tight. I only have about a total of 18" of height space to work with. I plan to cut off the old cast iron and steel vent and replace it with ABS so I can easily provide drainage and venting to the proposed bathroom. I can buy reducer fitting in order to change from 4" to a 2" ABS vent. I will certainly keep the slope between 1/8 to 1/4 inch/foot as I put this together.

Will it work? Thank you so much for your help.

 

[Terry]

I'm having a hard time seeing what is horizontal and what is vertical.
Two toilets back to back should not have a double santee or fixture fitting. A double wye is best if combining them, or two wyes.
The shower should have a 2" drain and p-trap and a 1.5" vent.
Kitchen sink a 2" line which can reduce down to 1.5" on the trap arm and vent.

 

[Sponsor]

 

[T Tran]

I'm having a hard time seeing what is horizontal and what is vertical.
Two toilets back to back should not have a double santee or fixture fitting. A double wye is best if combining them, or two wyes.
The shower should have a 2" drain and p-trap and a 1.5" vent.
Kitchen sink a 2" line which can reduce down to 1.5" on the trap arm and vent.

Thanks, Terry, for the comments. I'm attaching an updated pic to show the vertical/horizontal pipes. And I'm attaching the Tee for the toilets I plan to buy from HomeDepot.

 

[Terry]

That fitting does not work with toilets. This video was showing what a double fixture fitting did.
A double san cross is even worse.

One toilet can wye off downstream of the toilet on the left.
I also don't see a vent for the shower.

 

[T Tran]

That fitting does not work with toilets. This video was showing what a double fixture fitting did.
A double san cross is even worse.

One toilet can wye off downstream of the toilet on the left.
I also don't see a vent for the shower.

Ooh. Didn't see that coming with the Tee fitting.

I thought the new shower can use the air from the kitchen sink's vent it's there's nothing else using that vent besides that 1 sink.

I just don't have enough height under the crawlspace to put in 2 wyes for the toilets without cutting the 4" cast iron drain further down the path. So if I need to have 1 wye to the left toilet and 1 wye to the right toilet, I need to cut the 4" cast iron drain further down the path then?

I just realized you also said using a double wye 45 deg will work as well. I think I found one on HomeDepot. https://www.homedepot.com/p/4-in-x-...-DWV-All-Hub-Double-Wye-C5834HD4433/100178347. Looks like the toilets will have 3" drain size if I use this double wye.

 

[Terry]

The wye can be on the horizontal for the toilet.
One santee for the one toilet and downstream on the horizontal, add the wye for the second one. That prevents the loss of water in the bowls.
3" works fine for toilets.

Codes don't like to use a kitchen sink as a wet vent on a shower.

You can slap a 2" santee above the toilet and wet vent the shower that way.

Tub above the toilet on a wet vent.

 

[T Tran]

The wye can be on the horizontal for the toilet.
One santee for the one toilet and downstream on the horizontal, add the wye for the second one. That prevents the loss of water in the bowls.
3" works fine for toilets.

Codes don't like to use a kitchen sink as a wet vent on a shower.

You can slap a 2" santee above the toilet and wet vent the shower that way.

Tub above the toilet on a wet vent.

Sorry for still not being 100% sure so I decided to draw what I believe you suggested are ok. There's the A drawing and a B drawing. Are you suggesting B (has 2 wye's; one for each toilet) is the best option or is A (like what Kohler suggested) ok, too? Thanks for your help and patience with this newbie.