Closed cell spray foam- isolation performance?

krsman · 25th February 2010

Hello. I am in the planning stages of building a new home and along with that, a studio. I live up in icy cold MN and so, for thermal performance reasons, I am going to have the exterior envelope of the home insulated with closed cell spray foam.

My studio will be actually built into the garage but there will be a small portion of studio that will share a common wall with the main house. I am planning on building a 2 leaf isolation wall with double 5/8" drywall and at least a 1" gap between wall leaves. I have a graphic of the wall below.

If the builder was going to do the walls in the "standard" way, he would have the spray insulation installed all around the 2x6 exterior walls of the house. I would then build my studio side wall with 2x4 metal framing and use standard fiberglass insulation in that wall.

My question is: Can anyone tell me what effect this has on the sound isloation performance of the wall. Would I be better off using fiberglass on both sides of the wall instead of the spray foam for better STC?

I know the spray foam will do a superior job of sealing all possible penetrations but I also know that it is not super dense and also has some rigidity to it that may cause the wall to resonate on that side. One of my thoughts was to just have the contractor spray only 1" foam inside the 2x6 cavity for sealing purposes and then place fiberglass over the top of that (towards the studio side).

Anyone have some experience/knowledge on this? Ive looked at other threads and can't find the exact same scenario.

Thanks.

Kevin

SAC · 25th February 2010

Having not seen any qualified numbers, I have wondered the same.
But as you have correctly noted, while it seals exceptionally well, it is not at all high mass, and thus, while it will be useful for sealing, I doubt it will be of much use for stopping any significant amounts of sound energy.

A shame....

But as far as wall (energy) insulation, cost being equal, I think I would just go with the foam rather than the foam/fiberglass insulation. And then consider the necessary adjustments (mass air mass, etc) techniques for sound isolation/transmission. I doubt the combined foam & fiberglass would offer much advantage for the extra labor involved.

avare · 25th February 2010

Quote:

Originally Posted by krsman

My question is: Can anyone tell me what effect this has on the sound isloation performance of the wall. Would I be better off using fiberglass on both sides of the wall instead of the spray foam for better STC?

Spray foam for heat insulation has almost no impact on the sound isolation. Fiberglas/mineral woll can increase the sound isolation significantly. Do not use the spray foam.

Andre

Brainchild · 25th February 2010

I wonder whether the foam would effectively reduce the air space in the MAM system, thereby increasing the resonant frequency of the system, thereby potentially introducing a reduction in the useful transmission reduction. A one-inch gap between studs is pretty small anyway, so going all-fiberglass seems like it would be a safer way to go from that standpoint. Depending on the other properties of the wall of course. But if I'm understanding your idea correctly, the thermal insulation of this shared wall itself isn't a very important consideration.

krsman · 25th February 2010

Avare- thanks for the heads up. That is obviously the area of the wall I want the MOST isolation. The other areas either butt up to the open garage space (which I really don't care about) or the outside (and my neighbors will be quite far away). I will stick with Fiberglass or Rockwool for those areas.

Brainchild- you made an excellent observation and I suspect that you are dead on. By introducting such an rigid structure in the open space, you are gonna reduce the LF absorbtion ability of the 2 leaf wall system by reducing the depth of the open space. I had not thought of that before.

Thanks gentlemen. I hope this can be a useful thread for others in the future.

avare · 26th February 2010

Quote:

Originally Posted by Brainchild

I wonder whether the foam would effectively reduce the air space in the MAM system,...

Closed cell and self skinning foam DOES NOTHING ACOUSTICALLY.

Andre

25th February 2010	#1
krsman Gear interested Joined: Feb 2010 Posts: 13 Thread Starter	Closed cell spray foam- isolation performance? Hello. I am in the planning stages of building a new home and along with that, a studio. I live up in icy cold MN and so, for thermal performance reasons, I am going to have the exterior envelope of the home insulated with closed cell spray foam. My studio will be actually built into the garage but there will be a small portion of studio that will share a common wall with the main house. I am planning on building a 2 leaf isolation wall with double 5/8" drywall and at least a 1" gap between wall leaves. I have a graphic of the wall below. If the builder was going to do the walls in the "standard" way, he would have the spray insulation installed all around the 2x6 exterior walls of the house. I would then build my studio side wall with 2x4 metal framing and use standard fiberglass insulation in that wall. My question is: Can anyone tell me what effect this has on the sound isloation performance of the wall. Would I be better off using fiberglass on both sides of the wall instead of the spray foam for better STC? I know the spray foam will do a superior job of sealing all possible penetrations but I also know that it is not super dense and also has some rigidity to it that may cause the wall to resonate on that side. One of my thoughts was to just have the contractor spray only 1" foam inside the 2x6 cavity for sealing purposes and then place fiberglass over the top of that (towards the studio side). Anyone have some experience/knowledge on this? Ive looked at other threads and can't find the exact same scenario. Thanks. Kevin Attached Thumbnails

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25th February 2010	#2
SAC Registered User Joined: Dec 2009 Posts: 2,622	Having not seen any qualified numbers, I have wondered the same. But as you have correctly noted, while it seals exceptionally well, it is not at all high mass, and thus, while it will be useful for sealing, I doubt it will be of much use for stopping any significant amounts of sound energy. A shame.... But as far as wall (energy) insulation, cost being equal, I think I would just go with the foam rather than the foam/fiberglass insulation. And then consider the necessary adjustments (mass air mass, etc) techniques for sound isolation/transmission. I doubt the combined foam & fiberglass would offer much advantage for the extra labor involved.

25th February 2010	#4
Brainchild Lives for gear Joined: Jan 2009 Location: USA Posts: 989	I wonder whether the foam would effectively reduce the air space in the MAM system, thereby increasing the resonant frequency of the system, thereby potentially introducing a reduction in the useful transmission reduction. A one-inch gap between studs is pretty small anyway, so going all-fiberglass seems like it would be a safer way to go from that standpoint. Depending on the other properties of the wall of course. But if I'm understanding your idea correctly, the thermal insulation of this shared wall itself isn't a very important consideration.