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Old 04-26-2013, 12:03 PM   #1
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Encase PVC pipe in concrete for sound control?


I am in the process of renovating my two-story, plus full basement house, and all the walls and ceilings are open.

There is a second-floor bathroom above the first-floor kitchen, and I am concerned about sound transmission when someone flushes the toilet on the second floor.

The 3" PVC drain pipe for the toilet runs about two feet horizontally between the second floor joists (doubled/tripled 2x8s) before dropping down vertically into a chase on the exterior wall of the house (2x4, furred out to 2x6).

I don't want to rip out the new PVC plumbing that has been put in, and replace it with cast iron, which I've read has much better sound insulation qualities. I've looked into pipe wraps, but they seem to be quite expensive.

Beyond the additional weight considerations, does anyone have any thoughts on the following plan:

On the exterior wall, add 1/2" to 1" of rigid or spray foam to separate the chase cavity from the exterior wall cladding. Starting at the bottom of the vertical chase, add blocking/caulk to make the cavity mostly air-tight. Then, pour concrete in 1' sections around the pipe until I reach the top of chase, and repeat for the two foot horizontal section. The 9 vertical section would rest on the top of the basement wall.

I understand that I will have accessibility issues in the future if there are plumbing problems, but I don't think they would be much different than a PVC pipe buried in a basement slab.


Any comments are appreciated.

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Old 04-26-2013, 12:16 PM   #2
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Encase PVC pipe in concrete for sound control?


The PVC will not be able to expand or contract when embedded in concrete. I would fill the cavity with insulation or buy pipe wrap if you don't want cast iron.

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Old 04-26-2013, 03:11 PM   #3
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Encase PVC pipe in concrete for sound control?


Thanks for your reply.

I looked at the expansion value of PVC and found that it expands 0.9" per 100 feet for a 25 degree temperature change. I'll likely be installing it in 70 degree weather.

My vertical pipe will only be 90" long, so that means it would expand/contract 0.000675" for a 25 degree temperature change, or about 1/1500 of an inch.

0.90 / 100' x 1 ft/12" = ( 0.90 / 1200 ) * 0.90" = 0.000675, or ~ 1/1500 of an inch if the temperature changes by 25 degrees.

Even if the temperature drops down to -5 degrees (and which seems unlikely if the furnace is working), I'd only be looking at a 1/500 of an inch contraction.

Just to be careful, I will change my plans and I will wrap the pipe in a 1/8" sill plate gasket foam (like what they use on a foundation sill plate).
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Old 04-26-2013, 04:44 PM   #4
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Encase PVC pipe in concrete for sound control?


I'd just spray foam the entire cavity, or fill it with cut pieces of the 1" rigid foam. It will not only quiet down, but give you better insulation.

If filling chases with concrete was a good idea, other people would be doing it.
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Old 04-26-2013, 06:44 PM   #5
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Try wrapping it with foam rubber carpet padding and duct tape or zip tie it, and see how that works, you can usually find used stuff for free.
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Old 04-26-2013, 06:59 PM   #6
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Quote:
Originally Posted by toddmanqa View Post
Thanks for your reply.

I looked at the expansion value of PVC and found that it expands 0.9" per 100 feet for a 25 degree temperature change. I'll likely be installing it in 70 degree weather.

My vertical pipe will only be 90" long, so that means it would expand/contract 0.000675" for a 25 degree temperature change, or about 1/1500 of an inch.

0.90 / 100' x 1 ft/12" = ( 0.90 / 1200 ) * 0.90" = 0.000675, or ~ 1/1500 of an inch if the temperature changes by 25 degrees.

Even if the temperature drops down to -5 degrees (and which seems unlikely if the furnace is working), I'd only be looking at a 1/500 of an inch contraction.

Just to be careful, I will change my plans and I will wrap the pipe in a 1/8" sill plate gasket foam (like what they use on a foundation sill plate).

applies only to pipe not fittings your not calculating temperature of the mix during the curing proses and pvc is petroleum base those expansion values are good for about 3 years.
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Old 04-29-2013, 07:41 PM   #7
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Encase PVC pipe in concrete for sound control?


It's the vertical part, replace it with cast iron. You're wasting effort trying to half-ass something else. Just bite the bullet, rip out the PVC and replace the stack with cast iron. Lordy, it's EASY to do this now when the walls are open! PVC is cheap, it's not like you're wasting a ton of money ripping it out.
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Old 04-29-2013, 08:27 PM   #8
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/\ This!

Replace it with cast iron, problem solved.

I have PVC drains in my house. They are noisy compared to cast iron. I insulated the walls around the pipes using batts, it doesn't do much to help.

Another thing, it's not only the air temp that causes expansion/contraction noises, it's the noise when hot water goes down the drain after cold, or vice versa. That's more than a 25 degree difference, closer to 60 in some cases.

Your math is wrong by the way.

.9" per 100' = .9/100 or .009 per foot of pipe. You have 90" of pipe or 7.5 feet. .009*7.5 = .0675" of expansion in your run, just over 1/16".
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Old 04-30-2013, 05:09 PM   #9
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Encase PVC pipe in concrete for sound control?


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/\ This!

I insulated the walls around the pipes using batts, it doesn't do much to help.
What kind of batts? Roxul / Rockwool? That's what I'd opt for, as that's one of its common uses...sound deadening.
And then, I'd install Quietrock or a double layer of 1/2" drywall, if possible.
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Old 04-30-2013, 05:35 PM   #10
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Encase PVC pipe in concrete for sound control?


I used the JM Acoustic Insulation, it's a fiberglass batt product.

Don't get me wrong the stuff works well. You can't really hear any "noises" from using the bathroom, but when the pipes expand it does so with a "snap" noise.
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Old 04-30-2013, 05:53 PM   #11
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Encase PVC pipe in concrete for sound control?


No amount of insulation is going to help when the reverberating material is hard-mounted to the framing. The sound just rings through. Whereas with cast iron the material itself does the absorbing. Trying to stuff insulation around the pipe won't get to the noise that's transferred directly from the plastic to the wood.

The simplest answer is usually the best. RIP OUT THE PVC NOW WHILE IT'S OPEN.

Last edited by wkearney99; 04-30-2013 at 05:58 PM.
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Old 04-30-2013, 06:26 PM   #12
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Encase PVC pipe in concrete for sound control?


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Originally Posted by wkearney99 View Post
No amount of insulation is going to help when the reverberating material is hard-mounted to the framing.
And that's the problem. It needs to be supported somewhere.

Put in the cast iron!!!!
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Old 05-01-2013, 05:58 PM   #13
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Encase PVC pipe in concrete for sound control?


I like the concrete idea. How will you now handle the extra weight?

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