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Wall Assembly Retrofit and Sound Attenuation

digidoggie18 | Posted in Building Code Questions on

Hello,

When we bought our home 3 years ago it was done by a cheap builder. We are starting to see the issues where they cut corners. With that being said coupled with this we are trying to fix our settling issues. We live in the Pueblo, CO area and another issue is sound within the home. I can hear everything outside, we hear the highway, etc.. I want to rip the drywall out minus the drywall for the attic and start over using rockwool in par to help with the sound. With this being said, I know rockwool comes unfaced and dries and resumes its qualities. With that being said, will I need some sort of vapor barrier with it? I plan on sealing the internal stud cavities as well however, I’m not sure with what. Our exterior is stucco.

Tim

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Replies

  1. ROBERT OPALUCH | | #1

    To me, the settling issues seem like a problem that needs addressing first unless they are relatively minor. Just in case you might consider selling your home and moving elsewhere.

    Unfortunately sound can get to your interior through windows, doors or your attic as well as walls. There are window inserts specifically made to reduce sound as well as reduce wintertime heat loss. (Airtight high quality triple pane windows have a reputation for significant reduction in sound, but would be a very expensive improvement, not appropriate for a newly constructed home.)

    For modifying walls, there are many options. Others will suggest more options. Here are a few:
    - Air sealing improvements, including caulking cracks
    - Filling in the voids between your windows and the surrounding wood wall framing with low expansion canned foam etc. Remove the trim around windows, seal leaks, then fill the space with sound-absorbing material without squeezing the window frame that could impede window operation
    - Wrapping electrical boxes to reduce sound transmission through them, using specialty electrical boxes, making them airtight, or wrapping them with sound-absorbing "play doh" like products available for reducing sound transmission
    - Two layers of drywall, mostly gluing the second layer to the first
    - Type X 5/8" thick firecode drywall instead of standard 1/2" drywall (or maybe your cheap builder used 3/8"??)
    - Use specialty sound deadening drywall, a "sandwich" with a layer of sound deadening material between two layers of gypsum drywall
    - Mass loaded vinyl sheeting behind drywall is an excellent sound deadening material
    - Double walls, with a continuous layer of insulation between them, which also drastically improves the energy efficiency of the wall system (i.e., you could add an interior wall, but a lot of extra window/door/electrical work required too)
    - Horizontal 2x4's installed on the wall studs on the interior or exterior side, which allows more insulation to be installed, usually to reduce heat transmission (but also would reduce sound transmission significantly).
    - Drywall clips, which are strips of metal attached perpendicular to wall studs or ceiling joists, which hold drywall and reduce sound transmission significantly.
    - You certainly could replace the existing (fiberglass batt??) insulation in your walls with more sound deadening mineral wool batts. But I'd suggest doing cheaper surface treatments or a double wall rather than tearing out drywall and (hopefully decently installed) insulation. Maybe tear out some drywall in a less visible area like a closet to inspect the quality of the insulation work and wall cavities?
    - If you do tear out drywall and insulation, use caulk, canned spray foam or higher quality products to seal where your exterior sheathing meets the wall studs and top & bottom plates. Can be quick work to reduce air flow and sound through your walls, since your cheap builder may not have done a good job air sealing your walls.
    - Add an air barrier (NOT a vapor barrier, to avoid trapping moisture in your walls) if you tear out your drywall. Taped air barrier sheeting inside your wall should be "vapor open" not a vapor barrier.
    - Look up "airtight drywall" on this site for methods to make your drywall airtight, reducing drafts and heat loss, as well as reducing some sound transmission.

    Without knowing your lot size or the distance and the slope from the highway to your home...
    - Exterior brick/stone/concrete masonry walls or regrading your lot may reduce low frequency sound, the most difficult to attenuate, if you are considering building fences or walls around your property.
    - Your attic may be a source of more sound transmission, so some of the strategies for walls may help with your ceiling as well

    Hope a couple of these suggestions helps you live more comfortably in your new home. Best of luck dealing with a tough situation.

    1. Expert Member
      AKOS TOTH | | #5

      Great suggestions Robert,

      There is a lot of misinformation about MLV in walls on the internet. MLV is great for absorbing sound when hung loosely around a generator or a compressor. Sandwiched between wall layers about the only thing it adds is a bit of extra mass, barely budges the assembly STC value. Your money is better spend elsewhere plus the last thing we need is more plastic in our homes.

      One great option for retrofit sound control of older walls is dense packing with cellulose. You can dense pack right over existing fiberglass batts without having to take the drywall off. Besides adding a couple of tons of mass to your walls, it does a good job of air sealing older leaky structures. I have a place by a major street and dense packing the walls plus air sealing around windows and doors made a huge difference.

      1. Expert Member
        BILL WICHERS | | #6

        Akos, did you dense pack through cut holes, or did you open up the wall, dense pack, then put up new drywall? I'm really curious if anyone has had success with the cut hole method which I've heard about, but never tried or seen tried.

        I totally agree about MLV. I've lined some equipment chassis with it, but I wouldn't use it in a wall. Lead sheet would probably be at least as effective here, but I'd just use an extra layer of drywall maybe with green glue between layers. Drywall is cheap and relatively easy to install, and you get a lot of mass that way.

        Bill

        1. Expert Member
          AKOS TOTH | | #7

          The dense pack was done through holes on the inside, the original plaster and lath all stayed. There was insulation in the walls so it was a pretty simple install, from my reading about dense packing over batts, I don't think that would be that hard either. There was the occasional header extended across two bays and some bracing here and there which means some additional holes.

          Used a single hole per cavity about 3/4 of the way up the wall, to simplify patching I cut a larger rectangular hole right across the stud to access both cavities. Patching a larger hole is not much extra work and this way there is half as many holes to patch.

  2. canada_deck | | #2

    Robert gave a very comprehensive answer.

    A few more questions for you:
    - Are there any rooms that are better or worse? If two stories, is one story better or worse?
    - Are there particular sounds that seem to be better/worse at getting into the house?
    - Do you know what your current wall assembly is (siding type, sheathing, how thick are your walls, insulation, drywall)?

    Generally speaking, you will probably get the biggest bang for your buck by identifying weak points. Think of sound like water. If you have a small hole that is causing water to pour into your rowboat, you don't start by making the entire hull twice as thick. You start by just addressing the hole.

    One interesting observation in my house: Street noise is often the worst in the bathroom because of the way the bathroom vent was installed. You may find some other interesting situations. Perhaps the sound is getting into your attic via roof vents and your attic insulation is not done very well so it then travels through the ceiling. Fortunately, blowing extra insulation into an attic is cheap and easy and has other benefits (if done right.)

    It's worth it to spend more time trying to diagnose the problem before ripping down drywall.

    You may look into having a blower-door test done. That will give you a sense for how well sealed your house is before you start any of this.

    1. Expert Member
      MALCOLM TAYLOR | | #3

      C_D,

      I agree. Sound attenuation is only as good as the weakest link. You want to pick the low hanging fruit before resorting to replacing everything and finding out it didn't do much.

  3. Expert Member
    BILL WICHERS | | #4

    If you primary reason for wanting to put in rockwool is sound, I would advise against ripping the drywall out for that purpose alone as you are unlikely to gain much sound attenuation from swapping what are likely fiberglass batts for mineral wool batts. You would be MUCH MUCH better served for sound insulation by just putting a layer of 5/8" drywall directly over what you have now, and putting green glue between the layers. Better yet would be to hang that new drywall on resilient channel, which could also be done right over the existing drywall. You'd need to bring the electrical devices up flush with the new wall surface, which you could do with extension rings, and you'd need to seal them for sound which is a bit trickier, but doable (usually this is done with "putty pads" which are normally used for fire proofing).

    As others have mentioned, sound can still come through windows, doors, and just about anything else. You can get sound attenuating storm windows, which are normally made from laminated glass, as a retrofit for some existing windows. Good sound proof doors tend to be pretty expensive, so I'd try a good solid wood door first, or a foam core metal (or fiberglass) door with good perimeter weather stripping. Good weather sealing also helps with sound.

    I would only replace your existing insulation with mineral wool if you have to open the wall up for some other reason. Don't rip the wall apart just to put in mineral wool thinking that will help with sound as you're unlikely to notice any difference as long as the wall is insulated with something already.

    You need mass and decoupling for best sound proofing, and mineral wool adds only a little mass and no decoupling. Adding drywall adds mass, green glue provides minimal decoupling, and some other benefits, but it's easy to add when adding drywall. A big step up is resilient channel, and an even bigger step up would be a double or staggered stud wall, but those eat into your floor space. I think a double layer of 5/8" drywall on resilient channel is probably your best cost/performance option here, and if you do that your windows are likely to be your biggest weak spots.

    The Soundproofing Company has some nice illustrations of some sound attenuating wall assemblies here:
    https://www.soundproofingcompany.com/soundproofing-solutions/soundproofing-walls

    Bill

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