Question about PVC vs Cast Iron

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Justin S.

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Hello. I'm currently I'm in the middle of a whole house remodel and am replacing all of the plumbing. The house was built in 1947 and has a half bath on the first floor with a full bath above it on the second with the toilet from each sharing the same wall stack. That stack and the 30' horizontal run to exit the basement is all cast iron. All other bath drains (and supplies) are galvanized. The CI has surface rust spots all along it. My original plan was to replace all galvanized drains with PVC and tie into the Ci pipe. But, after researching, it appears that the CI pipe is at the end of its life. The most common lifespan I can find listed online is 75+ years with one source saying 50+.

It seems wise to replace the CI. However, this is the first 2 story house I've lived in and the bathroom is above the living room. My wife grew up in a 2 story house and never liked the fact that when the toilet flushed, the water going through the PVC pipes was loud. The CI pipe seems to be a lot quieter than the PVC and I'm wondering if just wrapping rockwool or something around the stack would get the noise level near CI or if I should try and replace it with another CI stack and do the rest in PVC? I would much rather do the full run in PVC if there was a way to quiet the water noise.

Hope that all makes sense and I welcome any thoughts on the matter.
 

John Gayewski

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I think i would try my best to baffle the sound like you said and tell your wife of she wants cast iron she can help you cut it.

Cast iron is fine, but it doesn't drain as well as pvc. A little and patience you could have a nice cast iron system, just know that it's more work.

I'm not sure anyone can tell you for sure how much insulation you need to make the noise in the pvc as low as it would be with cast iron. But insulation will do a lot to help.
 

Tuttles Revenge

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Adding a dense sound deadening material to the PVC can reduce the noise transmission levels to the same DB as Cast Iron. Material like Dynamat are materials i've used more recently.. lots of people use it in the automotive industry for sound transfer.

Installing CI will significantly increase installatinon costs.
 

Justin S.

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I had wondered about something like Dynamat. Having just moved to a much smaller town, I'm now realizing things like Cast Iron are much more difficult to obtain as well. None of the local supply houses carry it. I may try something like Dynamat, maybe even surrounding that with rockwool or something similar until the drain makes the bend into the basement. It has to at least help.
 

Jeff H Young

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Ive never ran PVC above ground (it was never popular here but gainning useage) So my experiance with ABS is from a sound stand point is it is noisy cast iron is king the other stuff and insulation Ive found never comes close to equal it just isnt close maybe there is better product I dont know. We used to do a sort of minimal amount of cast iron on the toilet risers and a lot of the piping in the joist bay above but once above the floor coinvert to plastic for lavs and vents. on homes with higher expectations
 

Tuttles Revenge

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I had wondered about something like Dynamat. Having just moved to a much smaller town, I'm now realizing things like Cast Iron are much more difficult to obtain as well. None of the local supply houses carry it. I may try something like Dynamat, maybe even surrounding that with rockwool or something similar until the drain makes the bend into the basement. It has to at least help.
The best sound deadening is achieved by layers of differing densities of materials. Each material cuts out a different wavelength. Isolating the pipe from direct contact with the framing members avoids direct transmission of sound as well. Places where the vertical pipe is supported by riser clamps can be rested on rubber or cork/rubber vibration pads.
 

Jeff H Young

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Cast iron you dont need anything but if these other methods are every bit as quiet thats great Im just a bit skeptic.
 
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dreamhomesmedia

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Cast iron you dont need anything but if these other methods are every bit as quiet thats great Im just a bit skeptic.
Would that make cast iron more cost effective, in terms of sound proofing? I'm left wondering if the expense of sound proofing materials is worth it.
 

Jeff H Young

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Would that make cast iron more cost effective, in terms of sound proofing? I'm left wondering if the expense of sound proofing materials is worth it.
I really dont know about the sound proofing other than tell you in my experiance Sound is zero issue with cast iron and big issue with plastic maybe these guys can make it just as quiet not my experiance.
 

Justin S.

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Thanks for all the thoughts. I may end up doing a little of both. It appears that only 1 local supply house even carries cast iron and have only a couple 10' pieces in stock. Others said they can get it in, but may take a while. Guess this is the problem with moving to a much smaller city/town. That, and materials being a good bit more expensive here. But, I could use a cast iron closet bend for the toilet and the 4" stack in the wall and transition to pvc in the basement. That might solve the toilet flushing noise while keeping cost down. Vents and everything else would be PVC. Since the cast iron appears to be no-hub, I'd just get a couple of heavy duty no hub couplings and torque them down while making sure that stack is properly secured before the PVC transition.
 
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dreamhomesmedia

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I really dont know about the sound proofing other than tell you in my experiance Sound is zero issue with cast iron and big issue with plastic maybe these guys can make it just as quiet not my experiance.
Do you know why cast iron said to be hard to find? It would not be good to have to rip it all out if only some of it needed to be replaced. Not sure how to handle that situation. I don't like the sound of pvc pipes myself.
 

Jeff H Young

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Cast iron never been hard for me to get although some fittings arent as available like 1 1/2 might cost more than 2 inch because on commercial use we dont use 1 1/2 at all its harder to work with in tight spaces .
If you are real picky about sound (and I totally understand if you are ) you will be happy with castiron but You might be ok with pvc I cant make that call
 

Sylvan

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We only do cast iron above 2nd floor for drains. Plastic is great for vents.

Cast Iron is safer and is non toxic in case of a fire, it has a 70+ life span, quieter, allows for better drainage as the fittings are normally longer radius, Sweeps Vs Ells.

For venting Plastic is ok
 

Jeff H Young

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On a 2 story house and noise being an issue Cast Iron is King . if you dont mind a little or a lot of noise go plastic I have no info on ABS vs PVC with regard to noise but ABS is noisy my opinion
 
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