Detached garage outer leaf - beef up vs spray foam

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Flight Feathers
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Detached garage outer leaf - beef up vs spray foam

Post by Flight Feathers » Wed Oct 16, 2013 9:40 am

Hi all

I recently moved to a house in NJ, and part of the deal was I got the detached garage to use as my studio. I plan on doing a true room within a room build with completely decoupled inner walls, with 2 layers of drywall, green glue in between. I was reading the Rod Gervais book - he mentions you can beef up the outer leaf of a garage by cutting drywall to fit in between the stud bays of the exterior wall, times 2, then caulk/backer rod/cleat. I'm sure this is very effective, but the dilemma I'm running into is time vs. money.

I've build out a studio before, so I am familiar with construction and soundproofing techniques, and how long these things can take. And my personal situation is quite a bit different than during my last build - I'm now married, have a kid, and a full time job. Any building would be happening between the hours of 9pm to midnight, in a very quiet residential neighborhood - not ideal.

So here's my question - what if I got open celled spray foam applied to the outer wall and roof rafters instead of the beef up drywall? I know the foam has no mass benefit, but it does have some sound absorption, not to mention creating an air tight seal and thermal insulation.

The foam would be done in a day - a huge factor. The drywall would take me I'm guessing 80 hours, over 3 months. Is the difference in the STC worth it?

I'd be happy to do 3 layers of drywall on the interior as well - it would go up so much faster than cutting individual strips to go in between the stud bays.


Thanks!
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Post by norton » Tue Oct 22, 2013 6:47 am

"Is the extra STC worth it..."

That's THE most important question to resolve.

The foam is not cheap...but it will create a fantastic thermal sutuation. However, any sound absorption will likely be due to the fact that all gaps will be sealed up tight. Which isn't a bad thing.

Filling the stud cavities with s rock, will give you added stc, but to what degree?

The bottom line is that a room within a room should give you an stc in the high 50's. it's an incredible slide of diminishing returns after that. High 50's stc is nothing to sneeze at.

What's the area like? Lots of semi rumble? traffic? Bus routes? Residential? Train lines?

I think the methodology you are proposing. Spray foam outer structure, and room within a room. Should be studied. To my knowledge, it hasn't. My guess is that if you do a reasonable job of the internal walls with gg etc.... The spray foamed outer walls will end up sealing out all those leaky high frequencies and you'll be left with only the extremely low end to worry about. It should be a very hi performing system.

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Post by norton » Tue Oct 22, 2013 6:53 am

And that guitar... Definitely a melody maker. The neck joint gives it away.

BUT, it's been heavily modified. Top and back woods and all binding have been added. Cool guitar. Hope the move and build out are smooth and easy.

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Post by Flight Feathers » Tue Oct 22, 2013 7:56 am

Thanks for the reply. My primary objective is to keep the sound IN, so as to not disturb the neighbors. It is a pretty quiet neighborhood, although there is some highway noise off in the distance, and a train line very close.

I'm actually wondering about a foam plus cellulose approach to the outer leaf. I've seen an application referred to as "flash and batt" where they do a thin layer of closed cell foam, which seals air gaps and provides a vapor barrier, then do the rest of the space with fiberglass, to save on costs. What if I were to flash with a closed cell to get the air seal and some thermal benefit, then fill the rest with dense cellulose to get some mass?

I know what I am talking about isn't cheap, but in my case, the savings in time is worth the money.
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Post by JWL » Tue Oct 22, 2013 7:57 pm

The biggest difference will be in the low bass frequencies, where the extra mass is essential (the more mass, the lower the resonant frequency of the wall assembly; frequencies below resonance pass much more easily). If you go the foam route, and you have traintracks close by, I'd expect condenser mics to pick that up.

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Post by JohnDavisNYC » Wed Oct 23, 2013 6:59 am

I'd say get some buddies with construction experience, take a weekend off from family life, and sheetrock the shit out of that thing. A good crew could get any garage done in two days.

Better to just do that way since it's known to work, and there is no risk. If neighbors and working at night are the issue, get as much rock up between those studs as possible.

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Post by DrummerMan » Wed Oct 23, 2013 8:24 am

Re: foam... If you go that route, wouldn't you want closed cell instead of open cell, fr the fact that closed cell will actually be more sealing ('cause the cells are closed)? Or is that not how that works?


I've been thinking about this very thing. My garage outer leaf is stucco over paper, no sheathing. That means micro (and not so micro) fractures all over the place, so the idea of spraying something to just seal it all up is very appealing.

I was actually thinking about spraying some close cell foam in a spot, then before its set, quickly throw up a piece of Sheetrock, sandwiching the foam between it and the paper. Was planning on experimenting with that soon.
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Post by MoreSpaceEcho » Wed Oct 23, 2013 10:50 am

JohnDavisNYC wrote:I'd say get some buddies with construction experience, take a weekend off from family life, and sheetrock the shit out of that thing. A good crew could get any garage done in two days.
agreed. one guy cutting pieces, a couple guys putting 'em up. lots of coffee. you'll be done in no time.

i think you are gonna want the extra mass...not just for keeping the studio sounds from disturbing your neighbors, but also the sounds of BUILDING the studio....putting pieces of drywall between studs actually wouldn't be that loud, you could do that at night (i assume you're gluing not screwing...or do the cleats hold them in place?), but framing up walls and everything else is likely gonna be as irritating to the neighbors as playing music in there...

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Post by Flight Feathers » Wed Oct 23, 2013 10:54 am

DrummerMan wrote:Re: foam... If you go that route, wouldn't you want closed cell instead of open cell, fr the fact that closed cell will actually be more sealing ('cause the cells are closed)? Or is that not how that works?

I've been thinking about this very thing. My garage outer leaf is stucco over paper, no sheathing. That means micro (and not so micro) fractures all over the place, so the idea of spraying something to just seal it all up is very appealing.
Well closed cell is very rigid, and thus has almost no acoustic benefits, ie absorption. We got closed cell in our attic and you can punch it hard and the only thing you hurt is your hand. That's why I was considering open cell. But I can find any stc data on assemblies.

I think in your case an initial layer of closed cell on the outer leaf would have lots of benefits - thermal, air seal, structural rigidity, and vapor barrier.
DrummerMan wrote: I was actually thinking about spraying some close cell foam in a spot, then before its set, quickly throw up a piece of Sheetrock, sandwiching the foam between it and the paper. Was planning on experimenting with that soon.
I know what you are saying, but doubt it would work. I think the foam needs to expand to do it's thing, if you throw drywall in there it would probably get in the way of expansion. And you would have to be super quick.
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Post by goose134 » Fri Nov 29, 2013 12:16 am

I did my basement ceiling to keep my drums from offending my first floor tenants. In the joist space, I put up a layer of rock with green glue on the back, then a second layer of rock with green glue. Then acoustic caulk.

I'm not going to say you can't hear me play drums anymore, but it certainly doesn't sound like I'm playing in the bedroom on the first floor.

I did complete the decoupled ceiling with 2 more layers for the finish (rockwool and two more layers of drywall with green glue). It makes a huge difference.

I used to be able to tell you what room their cat was in while I was in the basement. Now you can barely hear the drums. I'd imagine a similar treatment would do wonders on the walls.
I make a living as an electrician, not recording in the basement.

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Post by Nick Sevilla » Fri Nov 29, 2013 7:25 am

Hi and welcome to studio construction hell.
Just kidding.

If you want this done properly, do this:

1.- Determine what STC ou realistically need. You might only need 30-40 dB of reduction, since you are in a residential area.
2.- Create a budget.
3.- Try to stick to this budget.
4.- Consider using a contractor for the heavy building part. Consult a contractor to determine if the kind of 'remodel' needs permits or a licenced contractor in order to do in your city. Different cities have wildly differing codes about this.
5.- Consider not building from 9pm to midnight. Unless you really want to piss off your neighbors. And if you rent, trust me you do not want to ever piss off your neighbors.

Cheers
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Post by leigh » Sat Nov 30, 2013 7:18 pm

JWL wrote:The biggest difference will be in the low bass frequencies, where the extra mass is essential (the more mass, the lower the resonant frequency of the wall assembly; frequencies below resonance pass much more easily). If you go the foam route, and you have traintracks close by, I'd expect condenser mics to pick that up.
This!

I went the "flash and batt" route on my detached garage studio. One layer of 3/8" sheetrock hung on resilient channel for the inner leaf. I really wish I had beefed up the outer leaf with an extra layer of rock. Low freq engine rumble and even bouncing basketball sounds go right through the wall.

Leigh

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Post by jhbrandt » Wed Dec 04, 2013 9:45 am

Nick Sevilla wrote:Hi and welcome to studio construction hell.
Just kidding.

If you want this done properly, do this:

1.- Determine what STC ou realistically need. You might only need 30-40 dB of reduction, since you are in a residential area.
2.- Create a budget.
3.- Try to stick to this budget.
4.- Consider using a contractor for the heavy building part. Consult a contractor to determine if the kind of 'remodel' needs permits or a licenced contractor in order to do in your city. Different cities have wildly differing codes about this.
5.- Consider not building from 9pm to midnight. Unless you really want to piss off your neighbors. And if you rent, trust me you do not want to ever piss off your neighbors.

Cheers
A big +1

You said it Nick.

OP, I have several papers on my publications page that will help you determine how much isolation you need. Enjoy.

Mass and seal are that only way to accomplish sound-proofing. Gypsum board (drywall) is by far the cheapest mass you can buy.

A note on wall assemblies and STC; You can get up to around STC50-55 with a SINGLE partition. If you want to go any higher, you will need a decoupled two leaf assembly. - MAM system. Then you can go up to around STC80 & more. Remember, the higher you go, the more expensive it gets.. sort of on a logarithmic scale.

You will also find on my publications page 'ir761' which is loaded with testing data of wall assemblies. Note that the ratings are from a laboratory and 'real world' values will most likely be about -10 dB from listed.

Cheers,
John
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Post by joninc » Thu Dec 05, 2013 4:19 pm

This is an interesting thread - I wonder what you decided to do in the end?

I am in a similar situation as far as a building goes and have been told by my builder that I can't do the drywall on the exterior walls between the studs due to the fact that the moisture would be a problem soon (pacific northwest) and would likely end up with mold growth in there.

he suggested that is also not up to code.

we are considering spray foam as well or batts... again, like you, for thermal reasons...
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Post by jhbrandt » Thu Dec 05, 2013 10:51 pm

Cement board then. :)

Mass is mass. Mold will grow on the wood studs rather than on Cement board. It is the paper on gypsum board that the mold will eat.. it doesn't eat gypsum. You should seal it very well - caulk the perimeter between the studs, then cover/seal with a 6 mil plastic. This should seal off the concrete board to the exterior & if mold grows in there, it stays in there.
Then fill the stud cavities with light-weight fiberglass insulation.

Cheers,
John
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