Converting vertical cast iron drain to PVC

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38ppBBia

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This is my first post, hopefully I am posting in the right section.

I recently bought an old condo with all steel pipes and cast iron drains. I have a first floor and second floor bathroom, and the vertical drain goes down through the basement floor. I would like to replace all the drains with PVC. I've read with more than one toilet, you need a 4" drain, and currently, both toilets are draining into the single 3" cast iron. My question is, unless I'm breaking up the concrete to get to the junction below is there any point to going to 4" PVC? Would replacing the 3" cast iron with 3" PVC be a code violation? Thanks.
 

Terry

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3" will handle up to four toilets on a vertical stack.
3" handles up to three toilets on the horizontal, the fourth toilet needs 4".

dwv_b2.jpg


This drawing shows 3" waste lines for the toilets.
 

38ppBBia

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3" will handle up to four toilets on a vertical stack.
3" handles up to three toilets on the horizontal, the fourth toilet needs 4".

dwv_b2.jpg


This drawing shows 3" waste lines for the toilets.

Thank you!
 

Jadnashua

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Note, in some places, in a multi-family (high-rise) building, PVC piping is not allowed! So, you need to check on that before you start to tear it all out.

FWIW, CI is still considered a premium product, although most of the newer installations use hubless versus leaded connections. You may find a lot more drain sounds after you convert. Plus, it tends to expand/contract when draining anything hot, and that can make some sounds on its own unless clearances and expansion is carefully taken into account. Any place where it might be tight, it will make noises when it changes length during a temperature change.

Why do you want to remove it?

Now, if you have galvanized water piping, that was NEVER a good idea, so changing that out is a great idea.
 
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