Looking For Advice on Waste/Venting for Remodel.

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Drew Morrison

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Hello,

I'm new to the forum and looking for advice on a 3rd floor bath remodel. I have plumbed some sinks and a laundry drain, but this the most complex project so far.

This is a second bathroom using the main cast iron 'stack' in our home. I have access to a crawl space overhead (a small one but navigable, it's a Mansard Roof).

The previous owner hired someone who did not ad venting for any of the fixtures. I am confused if they were being lazy, or if they considered the stack to be providing venting for the tub, sink and toilet.

My setup will have a double sink, shower pan and toilet. I am hoping to move the toilet on the other side of the room (it was previously next to the stack). This will land the drain at 6'6" away, using 3" I believe this falls within code as long as the pitch is correct.

Please see attached image for my venting idea, which would involve creating a new 2" vent through the roof.
I have read that it's best to transition to a 3" at the roof, to avoid freezing in winter.

20160521_093018.jpg


Any advice or pointers would be much appreciated!
Thanks,
Drew
 

Drew Morrison

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Your first problem is the you CANNOT use the stack from the lower bath as a drain for your new one, since it is the vent for the lower bath.
Hi HJ,

Thanks for your response - are you able to point me in the right direction? I didn't think about the relation between the 2nd and 3rd floor bath sharing that stack. Had thought it was a 'wet vent' situation.

Trying to DIY the right way!

Drew
 

Terry

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Wet venting is only for bathroom fixtures on the "same" floor.
The vent stack from below would have other vents tied in, and the velocity from above would be a problem below.
Leave the vent alone, and bring up a new waste line for the third floor bath that can tie in "below" the other bath.
An example of stacked bathrooms here.

dwv_b2.jpg


Also on your drawing you showed a backwards wye for the lavs and shower. You can't reverse the direction of the flow.

1.5" trap arm max distance = 42"
2.0" trap arm max distance = 60"
3.0" trap arm max distance = 72"
 
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Drew Morrison

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Wet venting is only for bathroom fixtures on the "same" floor.
The vent stack from below would have other vents tied in, and the velocity from above would be a problem below.
Leave the vent alone, and bring up a new waste line for the third floor bath that can tie in "below" the other bath.
An example of stacked bathrooms here. Also on your drawing you showed a backwards wye for the lavs and shower. You can't reverse the direction of the flow.
1.5" trap arm max distance = 42"
2.0" trap arm max distance = 60"
3.0" trap arm max distance = 72"

Hi Terry,

Thank you for the info! I have to rethink the project, but I understand now. Will probably repost a revised drawing.

Drew
 
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