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alexislin

Sound proofing our floors

alexislin
8 years ago
I've bought a three unit building (one unit per floor) with family, and we're all moving in together. There will be young kids on the top two floors. We're doing a big renovation. The current flooring is a subfloor of maybe 6" wide planks, covered with hardwood. It does a great job of transmitting noise between floors :-/

The house is brick and block exterior with wooden joists. We are ripping up the floors to the joists on the top two floors, and I've come up with a subfloor design to try to minimize noise between floors, especially footsteps.

First, Roxul between the joists. Then the following layers on top of the joists:
- 3/4" AdvanTech ply
- green glue noiseproofing compound
- 1/4" cement board (probably HardieBacker), screwed down
- green glue noiseproofing compound
- 1/4" cement board, screwed down
- 1/4" rubber underlayment, glued down
- 0.31" CoreTec Plus flooring (this isn't part of the sound proofing... this is just the flooring that was chosen)

This raises the existing floor height by about 1/3".

We are also going to use green glue noiseproofing sealant around the perimeters of the walls.


Here were my primary references for the design:
http://www.noisehelp.com/soundproof-flooring.html
http://www.noisehelp.com/soundproofing-a-floor.html
https://www.nrc-cnrc.gc.ca/ctu-sc/files/doc/ctu-sc/ctu-n35_eng.pdf

The NRC article says:
"In such simple joist floors, the most important factor influencing the impact sound attenuation is the total mass of the subfloor and the ceiling layers."

So the cement board is mostly to add mass to the subfloor, and to act as a sandwich for the damping compound. The low frequency noises (footsteps) are reduced mostly through adding mass into the subfloor (if I'm reading the article correctly). The damping compound also helps.

The dense material (cement board) will help transmit higher frequencies - i.e. mostly airborne voices, music, TV, etc. I'm not as worried about these noises, but even so, the recycled rubber underlayment (resilient layer) above the cement board and beneath the flooring should help counteract the higher frequency transmission through the cement board.

Another quote from the NRC article:
"Adding a resilient topping on top of the concrete layer reduces noise levels at high frequencies and counteracts the effect of the concrete there. The combination of the two elements significantly increases the IIC (Figure 4). In other words, a soft floor covering combined with the additional layer of concrete improves impact sound attenuation at all frequencies, providing an IIC of 50 or higher."


Does this seem like a good subfloor design to reduce noise between floors, especially footsteps? Any suggestions?

Comments (24)

  • Judy Mishkin
    8 years ago

    carpets work great.

  • alexislin
    Original Author
    8 years ago
    @nnigrt Yes, that's right, carpets are best. We're going to put carpet in a couple bedrooms, but we need something easier to clean for the main living areas. Our kids leave lots of crumbs, like to paint, etc. Carpet would be a disaster within a week.
  • _sophiewheeler
    8 years ago

    Confine eating and painting to the eating area instead of all over the house. Then put down carpet with a good pad. Hard surfaces will always be loud.

  • alexislin
    Original Author
    8 years ago
    Sophie, that's a good suggestion, and I definitely understand that carpet is best for noise by a significant margin. But I don't want carpet throughout. Surely I'm not alone in that? I'm hoping for feedback on the subfloor design given a hard flooring. It may turn out that we need to get area rugs even after all this... but I'd like to give it a shot and see what happens.
  • Judy Mishkin
    8 years ago
    last modified: 8 years ago

    our friends live in a very high end condo all kinds of fancy sound proofing. you can still hear if someone drops a small item on the floor over their head.

    so, do wood floors for the future, over lay with inexpensive area rugs for now. the kids wont always be little. yes i hope a pro jumps in to tell you your between floor efforts will work, but i think you can buy a lot of (disposable) carpet for the same money.

  • PRO
    Mint tile Minneapolis
    8 years ago
    last modified: 8 years ago

    Do be careful, those 6" planks are likely under your bottom plates of wall framing? cutting those at perimiter can be risky....and requires you replace with cross blocking ....for new subfloor .....

    there is a lot to consider with your structure before "taking it down to the joists" need way more info and it starts with intended new finished flooring with sound reduction & deflection in mind and specifications of structure.....

    you dont per se' just start piling up the materials.! Iwould omit cbu in the equation, likely opt for 3/4 exp 1 bc ply , and 1/2" ply +noble sis.

    roxul will help....

    mayble lean on the tech support of the soundproofing chosen and coretec for 2 opinions as a start. Noble has very good tech support with commercial soundproofing backround......hope that helps....

    http://noblecompany.com/products/nobleseal-sis

  • alexislin
    Original Author
    8 years ago
    Tundra, thanks for your comments. Yes, the 6" planks are under the wall framing. My contractor is taking this into consideration. I am certainly interested though if you have any specific advice on safely removing that kind of subfloor.

    The intended final flooring is CoreTec Plus luxury vinyl plank. Our goal is to reduce noise transmission through the floor, especially impact noise, as much as possible. We have wooden joists, 12" o.c. on the second floor, 16" o.c. on the third floor. They are 3"x10". We are hoping to find a design that pretty closely stays within the 1.5" thickness of a standard floor.

    Does that help?
  • PRO
    Mint tile Minneapolis
    8 years ago
    last modified: 8 years ago

    just edited above, good to know you are looking at structure and having A contractor asess load bearing walls and deflection/span etc

    as a rule if the substrate 1x planks are in good shape its best tto secure and leave them, most always exp1 BC plywood is the ideal subfloor. but i dont look at sound reduction often enough.

    youre contractor will know when and where not to cut...... looking at load transfer and such. if older balloon framed wall cavitys ??? maybe roxul there ??

    also you can add sound reduction measures into the ceiling below.....

    alexislin thanked Mint tile Minneapolis
  • alexislin
    Original Author
    8 years ago

    Tundra, thank you!

    I looked at NobleSeal SIS and that stuff is expensive! Almost $3/sq ft. It's also quite thin - about 3/64". From everything I've read, thickness helps with sound reduction. I'll read more about it though. It appears that they have performance test ratings.

    Can I ask what you mean by "replace with cross blocking"? I wasn't able to figure that out.

    You referenced Exp1 BC plywood and I had to look that up. For anyone who isn't up on their plywood grades (like me), here's a good reference: http://homeguides.sfgate.com/plywood-grades-specifications-99412.html. 

    You're saying you would skip the cement board and use 1/2" ply instead. Do you have a specific reason for recommending against the cement board? Or does it just seem like an odd application to you?

    Thanks again!

  • PRO
    Cancork Floor Inc.
    8 years ago

    Green glue (which is not a glue) should offer (roughly) 18 dB worth of acoustic insulation. The rubber will offer another 12 dB or so. One person's "floor" is another person's ceiling. To be clear, many "wood frame multiple family units" have a subfloor that is "worth" 35-40 dB. Start looking at your numbers to see how some of this stuff compares:

    1) Green Glue sandwiched between plywood = 18 dB (requires the screw holes to receive the isolating foam/caulking)

    2) 1/4" rubber (which can off-gass for years) = 12-15 dB

    2b) Careful with the rubber underaly...Coretec does NOT allow this material nor this thickness...you may have to sandwich the rubber between plywood

    3) Roxul between the joists: 5-10 dB

    4) Regular drywall on the ceiling: 5 dB

    If you add up your basics: 40 - 48 dB You are WELL INSIDE the 'acceptable' for subfloor acoustics for a wood frame multifamly unit building.

    Acoustic drywall (5/8") will offer another 18 dB. If you replace the regular drywall with 5/8" acoustic drywall ($3/sf) you will bring these numbers up to 55 - 63 dB.

    If you wish to keep the old ceiling in place, you can add regular drywall (5/8") and use Green Glue between the two layers for 18 dB (works out to be $2/sf using regular drywall and green glue).

    Remember: pot lighting = NOISY. Anything that breaks the acoustic ceiling, makes for a noising living situation on the lower level. Track lighting is a better option.

    I HIGHLY recommend you check with CoreTec...that 1/4" rubber underlay may not be allowed. Sadly that removes 20%-30% of our acoustics...which is MASSIVE. Remove the rubber and substitute it for new drywall+green glue ceilings. It will be MUCH cheaper. That rubber is going to be $3-$4 per square foot....and it may not be allowed.


    alexislin thanked Cancork Floor Inc.
  • alexislin
    Original Author
    8 years ago

    Cancork, thank you, this is very useful information. I wish I could find those dB ratings online somewhere. Do you have a reference table?

    Have you ever put green glue between cement board? I was thinking two layers of the green glue in the subfloor... the first one between the AdvanTech ply (which is on the joists) and a 1/4" HardieBacker, and the second layer on top under another 1/4" HardieBacker. I don't know if that will get me 2 * 18dB though.

    You are absolutely right. I contacted USFloors to ask about underlayment for COREtec Plus and this was their response: "We generally suggest using padding no more than 3mm (1/8’’) thickness, comparable in density to rolled cork underlayment: 190 kg/m3 – 210 kg/m3 (11.7 lb/ft3 – 12.5 lb/ft3)". Thanks so much for this tip. I'll figure out what our options are.

    Pot lighting - also great comment. I originally had recessed lights in our kitchen plan, but I think I'll look into track lighting as you suggest. I wonder if surface mount fixtures are any better than recessed lighting? They still require a ceiling box...

    Great idea on adding another layer of drywall to the ceilings. We aren't planning to take down the existing ceilings, but should be relatively easy to just add the new layer of drywall with the green glue between.

    Thanks so much!!

    Btw, I looked up your company info. You're based in Vancouver? That's great - I'm originally from Victoria.




  • PRO
    Cancork Floor Inc.
    8 years ago

    @alexislin...thank you. I've been reading about and writing about acoustics for 5 years. I've read so many articles; referenced so many web pages; viewed so many "spread sheets" for each product that it is now in my head. If you went looking for everything I've read, it should cost you 5-6 months of searching/reading (40hr work week) about acoustics and materials tested. If you dig HARD ENOUGH you fill find everything I've written about...but you have another 6months of research ahead of you.

    My question becomes, "Why do you need cement backer board if you are installing Coretec floating flooring?" You would have a dickens of a time getting the backer board to sit over the green glue. You would have to contact green glue to find out what they recommend for subfloors and backer board. I don't think it can be used this way.

    And remember: backer board is NOT structural...it DOES NOT add to the
    rigidity of the original layer of plywood. It is ADDED to two-layer
    subfloor...not "instead of". Even though you plan on having 1.5" of subfloor, two layers of backer board does not help achieve the rigidity of that 1.5" plywood would offer.

    Remember: you want to find the Green Glue acoustic caulking for the screws. This material is used with drywall...I don't know if it is used/allowed with backer board. With all these layers, you may want to look into mass loaded vinyl. I know you are trying to add mass/density (which is why you are trying to work with backer board) but the backer board isn't the same as "poured concrete".

    I think you would be better off using the green glue between two layers of thick plywood (not OSB...real plywood) and give up on the backer board. If you MUST have it...have the top layer as backer board (the two layers of plwyood must be very close to 1.5")

    If you think adding a new layer of drywall to the ceiling, then take the money you saved on the subfloor and use ACOUSTIC drywall AND green glue...this should get you close to 26 dB in the ceiling.

    And just for fun, I've just helped a homeowner in Moncton NB with a triplex...he used 6mm cork underlay + 11mm cork floating floor (20.0 dB of insulation) in this space...and now he's having problems with the party walls. This worked GREAT for "up/down" noise...

    The building was not made with properly built walls (shared walls)...so he has to add drywall/green glue to the walls. One wall should cost him $1000. He needs to do this both sides =x 2. He's shocked that $2000 is what it will cost to "fix" this...whereas I've told him the $2K is CHEAP...usually it takes $5K to do basic isolation between "homes".


  • PRO
    National Hardwood Flooring & Supplies
    8 years ago

    How about cork underlayment , in Chicago high rises it is a requirement. Comes in 1/4" or 1/2" great sound rating.

    alexislin thanked National Hardwood Flooring & Supplies
  • alexislin
    Original Author
    8 years ago

    Cancork, thank you so much. This advice is incredibly useful for me. I'm a complete neophyte and all I have behind me is a bunch of Google reading.

    I contacted Green Glue, and here's what they said about the cement board: "Cement board is perfectly suitable for Green Glue use, and the way you mention using it between the plywood and cement board is how we would recommend the installation. At the end of the day mass is the most important thing when choosing sheet materials. The combination of the GG/cement board and the rubber mat is a great way to take away footstep noises.". But then... I'm sure they were happy to be selling two layers of green glue instead of just one.

    To be honest, no one else has liked the idea of the cement board. My architect, my GC, everyone on this thread... all seem to think it is, at best, a weird idea. So I might chuck it at this point and go with your suggestion of green glue between two 3/4" plywood layers (not OSB). That's tried and tested, and will provide a structurally sound subfloor.

    I had no idea that CoreTec was limiting my options! I'll switch to laminate! Now my only concern is raising my entire floor by an entire inch with the 1/2" cork and ~1/2" laminate.

    Thank you, thank you!!

  • PRO
    Mint tile Minneapolis
    8 years ago
    last modified: 8 years ago

    im curious as to St.Gobains tech support response...

    Alex said:

    "I contacted Green Glue, and here's what they said about the cement
    board: "Cement board is perfectly suitable for Green Glue use, and the
    way you mention using it between the plywood and cement board is how we
    would recommend the installation"

    In attempt to make you think even harder for your'e dinner......LOL

    So if you are following Hardiebackers installation specs or any CBU specs did you see that it requires being set in thinset mortar and then screwed/fastened. The thinset bonds well to plywood and hardie while filling any out of plane voids ...........still CBU offers nothing in structural smarts but a good bondiing surface for tile and here sounds like you would be better utilizing that 1/4' for sound abatement while improving youre subfloor rating w/plywood.....but you have now further peaked my interest..

    ? are you indeed telling us that St.Gobain OK's Greenglue can be bonded to Thinset mortars in this sandwich? They Ok'd /verified that?

    I see Cancork has opened your'e mind in the right direction .....very knowledgeable that Cancork, still you want to outsmart the Architect, GC, and reinvent a new buildup and I welcome your'e outside the box thinking... clearly you are immersed in your'e projects concerns and finding youre way .. cheers!


    alexislin thanked Mint tile Minneapolis
  • PRO
    BLDG Workshop Inc.
    8 years ago

    i've just skimmed through the responses but haven't found any mention of resilient channel. have you considered it for beneath the joists prior to re-drywalling the ceilings? mass is great, but the uncoupling effect of the resilient channel helps the vibration die away in the air space before the last piece of massing (the ceiling drywall).

    alexislin thanked BLDG Workshop Inc.
  • alexislin
    Original Author
    8 years ago

    Tundra, even though I've more or less abandoned the idea of using cement board in the subfloor, I've contacted Hardie to find out what they have to say about layering HardieBacker with Green Glue. I'll post any response I get.

    Resilient channel in the ceiling sounds like a great idea, but we aren't planning to take down our ceilings. It's not a complete gut, so some of the walls and most of the ceilings are staying as-is.

    One of my constraints is that the ceilings are 8' high. If I raise my floors by 1", then my ceilings are 7'11". I don't want to lose too much more height or it will feel like a cave.

    Thanks again everyone! I'll post any more info I get.

  • Kivi
    8 years ago
    You may want to do some research on USG's website. I used their acoustic drywall between our neighbours when we gutted our FL condo. It is remarkable how much difference it made in sound transmission. They also deal with floor assemblies and they seem to have a gypsum panel that is part of a several layer floor assembly which you might want to check into. It sounds interesting, and if it works as well as the wall panels I suspect you would be happy with the results.
  • PRO
    Trademark Soundproofing
    8 years ago

    I agree that installing the Green Glue between two layers of at least 1/2" sub flooring is better than using 1/4" boards, not enough mass in them. However if your trying to achieve impact noise control, you will also have to decouple the ceiling with Resilient Sound Clips and Channels.

    Also keep in mind while many types of underlayments etc. have certain DB reduction numbers, when these are installed in a system the actual reduction is much less. E.g. MLV on it's own has an STC of 27 when installed in a wall with drywall it only adds about 4 STC points.

  • malhi09
    7 years ago

    This discussion has been extremely helpful to me as well.
    I have a quick question regarding cork flooring and green glue. Would it be better to use 1/2" cork or two 1/4" with green glue in between?

  • PRO
    lickity split
    7 years ago
    Somebody may have said these I don't know but gypcrete, or mass vinyl if it's not toxic. We used it between apartments and couldn't here a thing. I'd be weary of layers because of floor squeaks.
  • PRO
    Cancork Floor Inc.
    7 years ago

    @mali09 - sadly Green Glue is NOT a glue. It has NO BONDING property what so ever. That means it won't "hold" two layers of 6mm cork (1/4") cork together.

    I've had installers use both the "double layer" of 6mm cork and the "single layer" of 12mm cork (1/2") and they ALL prefer the ease the 12mm cork underlay offers them. It is fast, solid, easy to work and it makes their job EASIER. And any time you make an installer's job EASIER, you make the job "cheaper".

    You are welcome to contact Green Glue to find out about the effectiveness of the product between two sheets of cork. It may work...or it may do very little. In any event it will add HOURS of work to your project. And adding HOURS of work to a project makes it even MORE expensive with little known benefits.

    If you can, 1/2" cork is the BOMB when it comes to acoustics. I've never seen anything like it! The "benefit : price" ratio is VERY good. The more you add to this simple model, you the lower that number becomes...you add PRICE but you have an unknown "benefit"....

    Have fun. Make sure your flooring accepts cork underlay. Not all of them do.

  • PRO
    Trademark Soundproofing
    7 years ago

    When using Green Glue between layers in order to achieve the very important component of "damping" in your floors. You need to use rigid layers. Therefore you would usually need minimum 1/2" thick layers as 1/4" is too flimsy. GG will also perform a lot better with heavier components as in 2 layers of plywood or OSB rather than cork. Some builders will use 2 layers of plywood with GG thereby getting mass and damping in the floor and then use a resilient underlayment as in rubber or cork on top of that for absorption of impact.

    Here is a video of installing GG between 2 layers of plywood on a floor.



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