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Sound attenuation between floors

I am constructing a floor assembly between a 1st and 2nd floor and may not be able to build up a deep floor assembly due to exposed ceiling timber joists (and the small footprint of my structure). I am considering using 2 courses of Advantec (subfloor) material with perhaps a mass loaded vinyl material in between the subfloor material.

I was wondering if anyone else has constructed a floor assembly that might reduce some of the sound transfer without resorting to a deep floor framed system. Has anyone had success solving this problem?

I also don't need a framed floor system to address wiring or ducts so I am trying to come up with a solution that might be reasonable (even if not optimal, I know).


Asked by John Brown
Posted Mar 15, 2017 7:54 AM ET
Edited Mar 15, 2017 2:40 PM ET


11 Answers

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A couple layers of fiberboard between the 3/4 plywood layers would be more cost effective than vinyl mass material. Homasote makes several products for this application. Using 2 layers with stagger joints and glue, no nails, would work best. Carpet would be best, but if you use hardwood, add a layer of cork between hardwood & plywood.

Answered by Richard Patterman
Posted Mar 15, 2017 9:51 AM ET


You also could use hat channel to decouple the ceiling drywall on the first floor. Stuffing the ceiling with fiberglass can help as well without adding a lot of expense.

Answered by Steve Knapp CZ 3A Georgia
Posted Mar 15, 2017 10:00 AM ET


Here is a link to several publications (National Research Council in Canada) on sound control that you might find interesting. When I was looking into it the process of soundproofing it was not as intuitive as I thought.

Answered by Rob Myers
Posted Mar 15, 2017 4:03 PM ET
Edited Mar 15, 2017 4:04 PM ET.


That was what struck me when I started working on sound attenuation assemblies for condo units. It isn't intuitive and simply adding sound dampening materials often makes little difference, or in some cases can make things worse. The most predicable results come from replicating assemblies that have been tested as a whole.

Answered by Malcolm Taylor
Posted Mar 15, 2017 8:47 PM ET


I may do a floor assembly. Could I do a floor assembly of just 2x4's or do they need to be 2x6's to have any effectiveness?

Answered by John Brown
Posted Mar 20, 2017 9:57 PM ET


An assembly just means all the different materials from the finished floor above to the ceiling below. Assemblies are given STC ratings indicating how much sound they attenuate. Removing materials from, or adding them to, a rated assembly can make them act in unpredictable ways.

A couple of examples:

- On party walls with two stud walls separated by a continuous gap, adding a 1" fibreboard between the two, which you would think would help, ends up reducing the STC rating of the wall.

- Strapping a typical finished interior wall and adding a layer of 5/8" drywall over the strapping will dramatically reduce the sound attenuation of the wall.

I'd suggest doing an internet search of STC rating for walls. You will find dozens of examples some of which may suit your situation. Another alternative is to consult an acoustic engineer. That of course will mean paying for the advice.

Answered by Malcolm Taylor
Posted Mar 20, 2017 10:22 PM ET


In many ways the techniques for preventing sound transmission are the same as those to prevent heat loss:

- On GBA we obsess about "thermal bridging". To avoid sound transmission having good isolation between materials is your friend. Appropriate rubber vibration isolators, air spaces, etc all help. One little "short circuit" between wall assemblies will ruin an entire scheme.

- On GBA we talk about blower door tests to find and seal air leaks. Similarly the tiniest hole in a wall or floor will transmit noise to the other side.

- On GBA we debate "thermal mass". Big hulking concrete slabs and block walls are definitely helpful to prevent sound transmission.

A few things that don't often come up on GBA:

- Avoiding assemblies that can act as a diaphragm and resonate when you walk on or hit them.

- Avoiding parallel assemblies when possible. Out of square, level and plumb, that is desirable here.

The best approach, as Malcolm indicates, is to hire an acoustical engineer. Of course all consultants cost money, and when I dealt with an issue for my house I came up with a plan myself. (In my past life I managed the construction of a number of television and radio facilities and had hired acoustical engineers.)

Our mechanical room is directly below our master bedroom. That is a totally lousy and stupid location, but necessary in order for a ground floor bedroom to have good emergency egress through a window. All of the HVAC, HRV etc assemblies in the mechanical room were installed with pads, rubber mounts, etc. The ceiling sheetrock in that room was installed on hat track mounted to vibration isolators screwed to the floor trusses above; it floats decoupled from the walls. Anything that does go through the ceiling is isolated with acoustical caulk. Our contractor will say to me that I was "meticulous", but I think back at the time I was probably a "PITA". (Another text abbreviation for you Martin.)

So did I get it right? Yes, generally. I can still hear the geo compressor when I lie in bed, but it's at background noise level and in a way comforting. Ah, the heat is on...

Answered by Andrew Bater
Posted Mar 21, 2017 6:32 AM ET
Edited Mar 21, 2017 7:50 AM ET.


As Andrew mentioned, sound studio types are a good source of information. As an example, here is a link to one discussion that I found useful:

Answered by Rob Myers
Posted Mar 21, 2017 12:52 PM ET


Thanks Andrew, Rob and Malcolm. I appreciate those links especially. Sometimes, one doesn't know what the technical "industry" term for the problem is. The STC information helps. I am trying to manage the overall height of my structure and I am considering how best to create the cavity that is sometimes described. The timber joists are going to be 24" OC so if I were to lay a floor system down, the joists would be perpendicular to the timbers. Given that reality, I'm wondering if I could even get away with 2x4 or 2x6 joists to create the cavity. I have completely isolated my service cavity elsewhere so the only reason I am considering this is for a little bit of sound attenuation. Basically, I could do T&G above the timbers or a 5/8" furring strip for 1/2" drywall, then 2x floor framing, then a course of Advantec, an underlayment and a floating engineered floor... OR lay down T&G and 2 courses of Advantec with some mass layer between them. I know this latter option uses zero separation but unfortunately I know there are some battles I can't fight with this project. Will I regret this decision some day? Maybe. FWIW, I will be the only one living in the house. Resale? Maybe.

I definitely will be re-reading that avsforum link. Thanks Rob.

Answered by John Brown
Posted Mar 22, 2017 7:36 PM ET


If your timber joists are that close together I'd be inclined to try and avoid another layer of floor framing. Using t&g as a ceiling, with some mass loaded sound deadening layer above, and a subfloor above that is probably the direction i would try and go. What you are down to then is finding an appropriate material, be it mass-loaded vinyl or something else. As Andrew said, the devil is in the details. Making sure there are no small gaps or flanking paths for the sound is key..
Good luck with your build.

Answered by Malcolm Taylor
Posted Mar 22, 2017 8:25 PM ET


Thanks Malcolm. I found something on the TF Guild Forum that suggests that route might be a reasonable way to go as well. I will refine an assembly and report back here. I agree that the devil is in the details. Thanks for following this thread and making helpful suggestions.

Answered by John Brown
Posted Mar 22, 2017 10:44 PM ET

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