Kerdi Shower Drain Question

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TomV8

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One last question? I know that you have to reduce the 2 inch drain to the 1.5 at the p trap but can that mean the p trap can be two inchs or it has to reduce before?

Thanks for all the help
 

wwhitney

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Definitely no reduction of drain size downstream of the p-trap. If you have an existing 1.5" drain you need to use, you must use a 1.5" p trap and reduce from 2" to 1.5" upstream of the trap.

Cheers, Wayne
 

TomV8

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Definitely no reduction of drain size downstream of the p-trap. If you have an existing 1.5" drain you need to use, you must use a 1.5" p trap and reduce from 2" to 1.5" upstream of the trap.

Cheers, Wayne.

Thanks Wayne.

And while i cementing the water lines i discovered i do have a existing vent that was buried in insulation. It's upstream of the toilet but the top the pipe is about 3.5 inches below the drop.

Think i can scrap the new vent or keep it?
 

wwhitney

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You'd need to draw a diagram of all the pipes including the vent you found, but unless the existing vent is attachable to the shower trap arm before it has fallen one pipe diameter (1.5"), or is dry venting a drain that the shower trap arm can join before it has fallen one pipe diameter, it will not help you vent your shower.

Cheers, Wayne
 

TomV8

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20220226_202658.jpg

Ok top one is the current version. Vent is on the left.

I could cut back the pipe and have a right angle and cut through the joists and then the trap would be at the same level (slope taken in consideration) see picture in next post.
20220226_202259.jpg
 

wwhitney

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On the plumbing, as I think I've stated before, you just need to have a dry vent come off vertically before the shower trap arm has fallen one pipe diameter. Since you're sticking with the 1-1/2" drain, the vent can be up to 6' away if you maintain a perfect 1/4" per foot slope, and having a LT90 in between is not an issue. If the recently discovered vent is on the 1-1/2" line before it joins anything else, and meets the above requirements, you can use it in lieu of the new vent you showed previously.

On the framing, the top and bottom flanges of an I-joist are not to be modified in any way. All pipes have to go through the web, and the manufacturer should have a diagram showing what the allowable size holes are. The joist with the notched flange will need a repair. The manufacturer should have information on how to do that as well.

Cheers, Wayne
 
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