I'm seeing spray foam used more and more around my area. In a few years we plan to build another new house now that we have a child. As such I'm trying to build a list of things to do different. How would this affect a theater? I would still use the same staggered stud, double drywall and green glue. But what would the spray foam do when compared to the old standards Rock Wool and Fiber Glass (The Pink stuff)?

Has anyone done tests on this?

I don't have first hand experience with this. But I did read at one point that it was not recommended due to the final state of the foam. I thought the poster said there is something about its rigidity that doesn't allow it to perform as well. Hopefully Dennis or another guru is hanging around and will chime in...

BTW - your comment about Apple shares a while back made me realize that I need to get off my butt, work smarter, and earn that early retirement!

I'm seeing spray foam used more and more around my area.

If you mean the type of spray foam that expands and hardens, it is not useful acoustically in walls.

--Ethan

Yeah that's the stuff. I see houses begin built with it all over this area. I didn't know how it would affect NRC or STC. But I figured it would be bad, great for R value I guess but bad for theaters. If that becomes the norm in this area when we build I'll just have them skip the theater area.

On the topic of Apple yeah I knew when I left Apple in 1996 that things were bad. But when I heard Steve was returning to the company I place my future in his hands. The guys is a genius. Whether you like him or not he has a way with seeing a good thing and making it better.

If you can afford to use it every where else but the theater do it. Foam works 10 times as good and fiberglass batts.

I was at a home show convention a couple of months ago and there was a guy with a booth that did foam spraying and I had a conversation with him about spray foams and their application for sound control spaces.

He showed me a bunch of samples of different foams he used. He had one variety that actually dried "sponge soft".

For sound proofing rooms he said he sprayed it as a one to three inch layer to form an air tight seal (rim joist area for example) then recommend that the remaining space get the pink fluffy.

For internal sound control walls he again recommend just a layer as seal but not to fill the wall cavities from wall to wall.

I know in my next house I'm going to have the rim joist area sprayed to eliminate that major source of drafts in my house. But I can't see using it for internal walls. I could see doing it around the rear of all the electrical boxes if you have access.

I'm going to use the fire blocking foam in all areas but the theater. In the theater I'll be sticking with rock wool for the fire blocking along the top of the wall sill plate and the cement outer walls. I figure that the foam would baiscally defeat the my attempt at decoupling the room from the rest of the house if I used it in the theater.

That is a very good point, the foam does seal the leaks up. Maybe someone will do test on this 1-3 inch + fluffy stuff in the future. I'd say we are probably 3-4 years from another build but my wife an I are stating to have plans put together. We want to refine the plan over time so it will be ready when we build. The last new house was a a challenge really had little to any idea what we wanted.

The minimal expansion method would be valid in a staggered stud for the portion of the cavity NOT coupled to the room.

They basically carve this stuff with a big electric knife, and you would want to keep the rigid stuff off the secondary row of studs that the room's wall material will be attached to.

The product is called icynene foam, and there are plenty of threads here on this topic.

The stuff that dried "sponge soft" is the open cell version, and the rigid stuff is closed cell.
Closed cell is generally used below grade, and the additional rigidity can shire up loose stacked rock foundations like we have in older homes in the Midwest...
Open cell is commonly used above grade, and in addition to the intended insulation benefit, it will also provides a sound isolation benefit.

As an experiment, go to the hardware store and buy a can of Great Stuff expanding foam, and a can of DapTex expanding foam.... Great Stuff is a rigid, closed cell product (and MESSY to clean up) DapTex is an open cell product, and just so happens to clean w/ soap and water.

A couple years ago, I removed the casing around all the windows and doors and used DapTex.... My energy bills went down tremendously, AND the ambient noise level went down as well... I wholeheartedly recommend the product for that application, and it would be very useful as a tool to deal with penetrations in an HT as well.

One bit of warning, don't let this stuff dry on your skin. When I experimented with a can of the Great Stuff I accidently got some on the back of my wrist/hand even though I was wearing gloves. I must have wiped it off, but not truly cleaned it off. The next morning I noticed that there was a crackly film on the back of my wrist/hand. When I scraped it off it took all of the skin with it. The wound ended up looking a lot like a burn.

Oh I have used that stuff before I know how messy it can be. Almost as bad a sheet of Drywall with Green Glue breaking on your head.. Now that was hard to get out of my hair...

Open cell (spongy) vs. closed cell (rigid).

Open cell better for acoustical isolation.

Thanks so much for the primer; exactly what I needed to know to make a decision today about spray foam.

Open cell foam isn't "open" from our perspective. They'll argue that point but its the way it is

I used urithane foam for part of my roof insulation, but I wouldn't recommend it unless it lets you eliminate vents. Not only is it very expensive, it dries stiff, and transmits sound like styrofoam. Scratch or tap one side of it, and you can hear it on the other side no problem.

Since there was an 18" gap between the ceiling and roof, I added urithane foam to the underside of the roof, then filled the rest of the gap with loose-bat R-30 fiberglass.

Because sprayed foam doesn't require venting like regular fiberglass, I was able to eliminate the "eyebrow" roof vents I would have otherwise needed to pass my building inspection. That's the only reason I used it.