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Sound transmission disaster, now what?

Posted by SusanCF (My Page) on
Sun, Feb 26, 12 at 20:04

This feels like a disaster to us, at least. As part of a very extensive remodel, we're adding an in-law unit with the idea of renting it out to pay for a significant portion of the remodeling loans. (Everything is being done legally and by professionals.)

From day 1, we emphasized to our architect and contractors that sound separation between the units, which share a wall, was critical. However, there is no wording about this in the construction contracts. Although we are building neophytes, we thought our concerns had been adequately addressed -- for example, a second interior wall was built to separate the units, we understand the walls are all very well insulation, and (per city code for multi-unit structures), there is a one-hour firewall between the two parts of the building, all the way up through the attic to the roof.

But we had no way to test the effectiveness of the sound insulation until now, when the sheetrock is up, the cabinets are in, and the doors and double-pane windows have been installed. We are, or should be, very near the end of the project.

Our test was a disaster. From either unit, music played loudly in the other unit was perfectly audible. Even at likely "normal" listening levels, a radio played in the living room of the main house came through clearly in the bedroom of the in-law unit. We imagine conversations will come through the same way. It feels like there was no special sound blocking done at all. This is exactly what we were trying to avoid.

What now? We plan to call a meeting with the architect and builders, but what can be done at this late date? The in-law unit is too small to add anything to the walls on that side, but could we put something up in the house to mitigate the problem? Not something ugly, though, because it would be in our living room!

I am just at a loss and wondering what we can possibly do now. I would like to have some suggestions to make when we meet.

Follow-Up Postings:

RE: Sound transmission disaster, now what?

"we understand the walls are all very well insulation, and (per city code for multi-unit structures), there is a one-hour firewall between the two parts of the building, all the way up through the attic to the roof. "

Fire walls are not designed to stop sound transmission, just reduce the rate of fire spread.

Was any acoustica insulation placed betweenthe two walls?

Extra layers of drywall? (Even on a fire rated wall more layers helps with sound transmission fron the greater mass.)

Is the extra wall steel studs?

Was sound caulk placed under the top and bottom plates of the extra wall?

The builder likely followed plans the architect provided and you approved.

Any issue lies with the architect.

RE: Sound transmission disaster, now what?

no wording about this in the construction contracts

Yet a second wall was added between the units. Something's not computing.

Your problem may be flanking sounds--under and around the wall--that were not addressed.

RE: Sound transmission disaster, now what?

Ductwork? We totally forgot about the air returns when we finished our basement. The ductwork was not designed by the architect and the hvac people hooked up the new air returns to the existing ones. Now the kids use them as intercoms between floors!

RE: Sound transmission disaster, now what?

There is little to nothing that can be done at this point unless you are up for some deconstruction of the wall assembly. Add in some carpet and drapes and other soft surfaces that will absorb sound.

RE: Sound transmission disaster, now what?

Designing structures to reduce sound transmission (STC) and impact transmission (IIC) is best done beforehand. But it's hardly hopeless to retrofit. And you don't have to tear walls down to do it. Often added mass and/or sound damping drywall in conjunction with sealants are enough to do the job. But don't forget flanking sounds; and as scrappy points out, ductwork.

RE: Sound transmission disaster, now what?

Thanks to those who replied. My husband reviewed our building plans and found that Quietrock was used as the sheetrock for the the second wall that was built between the units, which is also the 1-hour firewall. We guess that the architect thought that was sufficient soundproofing.

My husband sent the drawings to another architect in our area who specifically works on soundproofing. That person replied, in part, that the new walls were not properly designed to achieve sound reduction between living units. He said, for example,

"The code minimum for a wall between units is STC 50 and with the resonances you now most likely have less than that. Most modern condo owners will have an expectation of STC 65+ - in your case where your living room is right up against [the other unit's] bedroom, it would have to go up to STC 70 for people to go about their lives and habits without hearing each other."

He referred us to the following page (which I skimmed but didn't understand) for why the design was inadequate.

He suggested that we would need to tear out the existing walls, including the newly-built firewall, and re-build them to properly address the resonance problem. We are hoping for a less extreme solution and are going to meet and discuss other possible remediation. (After all, what if we didn't own both units? Surely there must be a way to reduce sound transmission while working only from one side.)

If anyone reading this is going to remodel and is interested in soundproofing, please consult with someone with specific expertise during your planning stages. It was a costly error for us not to realize that was necessary.

RE: Sound transmission disaster, now what?

Add a layer of 5/8" sheet rock. Recently finished a very large office layout for a defense contractor that requires quiet rooms for foreign nationals. Outside office wall and inside ceiling 1 sheet 5/8" sheet rock, inside walls 2 layers of 5/8" sheet rock all metal studding, this is Military spec. I was skeptical at first, but I assure you these offices are extremely quiet.

RE: Sound transmission disaster, now what?

Call Quietrock to speak with technical services. They told me adding another layer of drywall actually reduces the STC, making transmission worse. Air is the best.

You not only need someone specialized to design, but someone specialized and meticulous to install the products. I don't know if there are certifications but who installs is very important. Be very cautious there verifying they are trained and thorough about their work or you have wasted your design and product money. These regular guys who say sure they install soundproofing materials don't know squat.

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