Ron Hazelton

How to Quiet a Noisy Drain Pipe in the Wall

Bathroom

Plumbing

HOUSE DOCTOR Transcript

HD030 “WALL DRAIN SOUNDS” from episode 303-F

RON:

Wow, can you hear that? That's the sound of water running inside the wall right here. Hey Joel, how you doing?

JOEL:

Hi Ron.

RON:

Joel was upstairs actually flushing the toilet on the second floor. There's a bathroom right above us here.

JOEL:

That's right.

RON:

And what we heard was that waste water coming down through the drain pipe inside the wall here. Now you've also had this problem sometimes when you fill the tub all the way up.

JOEL:

That's right. It's both the tub and the toilet from the master bathroom as the water drains is coming down straight from here.

RON:

Okay.

Well, you know, I'm not sure what the cause of this is. We could have some kind of strange plumbing arrangement in here that's causing this noise. Although I think maybe what's happening is there's some kind of harmonic that's being set up inside the wall here that's actually amplifying the sound of that water falling through the pipe. But I think the first thing we're going to have to do regardless is open this wall up, take a look and then go from there.

Now, using a stud sensor, I've determined that we've got a wall stud right there. There it is. That's the left-hand edge right there. The right-hand edge is over here. This is just about the middle of it. And also, we've got one over here. In between these two studs,

I'm getting some very strange readings. It actually indicates here. Let's take a look at this. It actually indicates there's something that's almost solid all the way across here. And this, by the way, is the bay where that pipe is located. So what I want to try to do now is to cut out this section of sheetrock as cleanly as I can in the hope that I can actually reuse this because it does have some wall texturing on it. So let's give it a try.

Now, what I'm doing now is trying to cut this sheetrock right on top of the stud right here. Actually, I want this cut right in the center. That's so that when I put this back, I've got something to nail this piece into.

Well, so much for taking this sheetrock off in one piece. You can see this is put on with screws and mesh tape. It just isn't going to come off without destroying it. So anyway, we're making some progress here. You can see what we've got.

This is a waste pipe right here, a 3-inch waste pipe. This looks like it might be a vent over here.

Well, I'm just taking out the last of this fiberglass insulation. Now, this is good insulation for heat. It has practically no value in terms of sound insulation. So anyway, I'm going to have Joel flush this toilet one more time. Okay, Joel, go ahead and flush it.

Yeah, that's just as loud as it was before. You know, I think the time has come to get some professional consultation here. So I'm going to talk to a plumber and decide where we ought to go from here.

Well, I called my plumber friend, Lee Marymore, and he asked Tim here to come over and take a look at the problem. Hey, Tim, thanks for stopping by. I flushed the toilet for you. You could hear this noise. So what's going on here?

TIM:

The water is circulating around in your pipes, and I recommend that we change this out to cast iron at this time.

RON:

So you're saying that the water is spinning around the inside of this pipe just like it does on a toilet when you flush it?

TIM:

Correct.

RON:

And that's what's causing all this noise?

TIM:

That's right.

RON:

Why the noise in the plastic?

TIM:

Because the density of the plastic, there's no insulation on there. Your cast iron is more dense, so it's going to absorb some of that sound.

RON:

Okay, so what's the first step then? I guess we're going to take this out, right?

TIM:

Well, I think we should look down below. We're going to see what's happening down there and make our determinations there. But, yes, this will have to come out.

RON:

Okay.

Well, obviously, we're down here underneath the house in the crawl space. I guess this is where the plumbing comes through, Tim, right?

TIM:

Right. This is that 3-inch stack that we're seeing up in the wall that's coming down.

This is our thing that's making the noise. But we may have some further noise down here. We won't know until we get this replaced.

This noise may be just dissipated in this space, not up above. But if it's echoing, it could come up through that vent line.

RON:

So you're saying that you might have to replace some of this as well.

TIM:

Correct.

RON:

But for now, we're just going to replace that and see what happens…

So where do we begin, down here or up there?

TIM:

We'll go upstairs, make our cut up there.

RON:

To begin, Tim marks the top of the plastic pipe one inch below the fitting. Then, using a reciprocating saw with a fine blade, he cuts through, being careful not to penetrate the opposite wall. Next, he marks the pipe at the point where it passes through the bottom plate. We'll explain why later.

Back underneath the house, Tim cuts the pipe free at the bottom. Then he cuts the pipe in half for easy removal.

Using a power miter box fitted with a metal cutting carborundum blade, Tim cuts the cast iron pipe to length. In order to fit the pipe into the wall, he also cuts the cast iron into two sections. Remember that mark we made on the old pipe? Tim transfers it to the new pipe and positions a support collar on the mark.

Cast iron pipe is heavy. When clamped in place, these collars prevent the pipe from slipping downward under its own weight.

Down below, Tim guides the new pipe into position. A special rubber gasket and stainless steel band connect the iron pipe to the plastic.

A similar fitting connects the two sections of iron pipe together.

Next, he aligns the two sections of iron pipe. When they're in position, he slips the metal band into place and tightens the screws.

Finally, he secures the screws on the upper clamp.

Well, it's better. Still a little bit too noisy, at least for me.

TIM:

Okay, why don't we go downstairs and I can see what we're running up against.

RON:

Okay, good.

Wow, that's quite a bit of noise down here.

TIM:

Yeah, I think that what is happening is that it's coming down hitting the plastic L45 here and the noise is reverberating back up through our pipe and vents.

I believe we're going to have to replace the Y45 and the combination 45Y and get our water going on horizontal.

RON:

Well, Tim's replaced this plastic drain with this cast iron. Let's go upstairs and see how it sounds.

Well, you know, the sound is still there. It's a little bit metallic now. What do you think?

JOEL:

I think it's about 50% better.

RON:

Yeah. Okay. I'll tell you what. Let's go ahead and put the sheet rock back on. I think that's going to help a little bit and then take one final listen.

Here's our piece of sheet rock. We've got this cut to size. Now, could you all push that in and put a fair amount of pressure right here. I want to push that pipe back. And we'll attach this in place with sheet rock screws…

Anytime you join two pieces of sheet rock like we're doing right here, you've got to cover this gap or joint right here with tape. Now, you can use a mesh tape or a paper tape, but whichever one you use, you've got to sort of put down a bedding coat of compound in which to kind of seal that tape, if you will. So that's what we're doing right here. In this case, we're using the paper tape. Just hold that right there handy, Joel. Actually, the mesh tape, you put the tape down first, then put the compound on top. But for the paper, put the compound down first. Lay the paper in the joint compound like this, centering the tape over the joint. And then using your putty knife, it's about a 5-inch knife, you want to kind of press this into that joint compound, just like that.

We'll need a couple more coats of joint compound on this, then of course we'll have to match the surrounding wall texture. We won't get into that, though, in this segment. What we did try to do here, though, was to quiet that noisy drain pipe. So let's take one final listen, Joel, if your wife could flush this one more time.

JOEL:

Okay, one more time, last time.

RON:

Okay, well, you know, if this helped, the sheet rock helped a bit. You can still hear it.

So what do you think?

JOEL:

I think it's a heck of a lot better.

RON:

Okay. I'll tell you what. We've done all we can do to quiet this thing down. If you have any ideas on how we might make this a little bit less noisy, even, than it is, give us a call or drop us a line, will you, and we may try your suggestion.

Joel, thanks for having us over. It was a challenging problem, I've got to say.

JOEL:

Thanks a lot.

From the archives of the House Doctor

If you've ever flushed an upstairs toilet and heard a loud rush of water inside the wall, you know how annoying a noisy drain pipe can be. In this House Doctor episode, homeowner Joel had exactly that problem, and it was loud enough to hear from the floor below. Here's how we tracked down the cause, what we changed, and how much quieter it got.

Water Noise Inside the Wall

Joel's second-floor master bathroom sits directly above a first-floor room. Every time the toilet was flushed, or the tub was filled all the way and then drained, you could clearly hear wastewater rushing down through the wall.

Ron couldn't tell right away what was causing it. It could have been an odd plumbing layout, or a kind of harmonic effect inside the wall cavity that amplified the sound of water falling through the pipe. Either way, the only way to find out was to open the wall.

Not sure what's behind your wall? Our guide on how to cut an inspection hole in a wall shows how to make a clean opening that's easy to patch afterward. And if you're worried about hidden pipes or wires, a handheld wallboard saw makes less dust and lowers the chance of cutting into plumbing or electrical lines.

With the drywall out, the cause of the sound was easier to see. In this instance, insulation turned out to be part of the story. Fiberglass batts are good at slowing heat transfer, but they do almost nothing to block sound. Even with the insulation removed, the toilet was just as loud as before.

Why Plastic Drain Pipes Are So Noisy

To get a second opinion, Ron brought in Tim, a plumber. Tim's diagnosis was that the wastewater was spinning around inside the pipe, much like water swirls in a toilet bowl when you flush. In a thin-walled plastic pipe with no insulation around it, that swirling water makes a lot of noise.

Cast iron is much denser than plastic, so it absorbs more of the sound. Tim recommended replacing the plastic section of the stack with cast iron.

Key Takeaways for a Noisy Drain Pipe

Plastic drain pipe with no sound insulation can be very loud when water swirls down a vertical stack.
Standard fiberglass wall insulation helps with heat but does very little for sound.
Swapping a section of plastic drain pipe for denser cast iron can cut the noise noticeably.
Fittings at the base of the stack, like elbows and Y fittings, can add noise of their own.
Closing the wall back up with drywall also helps quiet the sound.
For major plumbing changes like this, it's worth getting a plumber's opinion before cutting into the pipes.