Help! My exterior garage walls are rigid foam insulation!

Man, I think I'm really screwed here. I just took off the drywall on the inside of the garage and all I have is a stiff foil backed styrofoam attached to the studs on the other side! Then there's black paper and then vinyl siding- that's it! Is this legal? How am I going to beef up the exterior walls now? Please help!

Are you sure it's foil-backed styrofoam? Could it be Thermostat® OSB Radiant Barrier Sheathing or something similar?

--Keith :mrgreen:

I don't know what it is but it's rigid and yellowish and foil covered insulation... and not wood. The house is about 15-20 years old. .. I stuck a screwdriver right through everything with very little effort! I'm freaking out over here...

Is the garage attached to the house, or is a detached garage? It might be that the areas nearest the corners have sheathing on them to make the wall more rigid. I am also surprised! FYI, vinyl siding is not a good outer layer for studios... Vinyl siding is nearly impossible to "beef up." You're usually looking at a third leaf situation. How averse are you to replacing the siding and styrofoam on that wall with OSB, some styrofoam, and perhaps an inch of stucco? :roll: For some inspiration in stucco matters, see this post -- that's me helping Marc (guitardad72) in Florida during a vacation six months ago! :lol: I'm afraid I can't guarantee my availability to offer manual labor on your project... But if we can do it, then surely you can! :-) --Keith :mrgreen:

There's no way I'm taking the vinyl siding off and/or doing stucco- it's just not feasible... I guess I'll have to beef up the inner leaf- the dreaded third leaf - Ugh! Maybe two layers on top of existing garage interior drywall with green glue in between... Then build the studio with some serious mass- like 3 or 4 sheets of drywall... This hurts.

Actually, it's worse than that I'm afraid... :roll: ...One very beefy leaf next to two extremely wimpy leaves is going to be really bad for isolation... Ideal: MASS - AIR - MASS Yours: MASS - AIR - MASS - AIR - MASS Sorry, that's just the way it is. I'm thinking you're going to need a substantial amount of mass on your middle leaf to even get close to any amount of decent isolation... --Keith :mrgreen:

I'm hoping for a few more opinions on this one. Here's a question, with that rigid foam and the vinyl siding, how well will that produce sound? I mean, it's not drywall...

Ah, I misunderstood your plan. After seeing your illustration and rereading your post, yeah, that could work... Although you will still have a third leaf effect. What concerns me the most is the rattle and hum potential of that vinyl siding... :roll: You might end up with a relatively small leakage overall, but a particularly offensive low frequency from the kick drum or the bass amp may cause the siding to vibrate sympathetically, and that vibration might end up being the source of a lot of noise. Or not... :roll: ...There's no way to know for sure unless you actually build it and then test it. An expensive test that would be if the scenario I described turned out to be true. In my project, I too will have a third leaf along the back of the studio wall, adjacent to my office. It is my hope that my "overkill" mass and generous air gap between the inner and middle leaves will mitigate the effect of the third leaf, but I am mindful that I may have to beef up my 10' x 10' office wall by adding a layer of 5/8" drywall to it, probably with Green Glue, if it becomes a problem down the road. Unfortunately, vinyl siding is simply not "beef-uppable." :roll: --Keith :mrgreen:

Just use one air cavity in those walls (altough since the mass of that third wall is much lower than the other two walls we may discuss if this is indeed a rtriple leaf or not) Are you going to treat the floor as well ? I have used this product in my acoustical projects and it works OK http://www.texsa.com/int/productos.asp?lan=2&AP0=3&AP1=21&AP2=60&pr=365

andrebrito wrote:

Just use one air cavity in those walls (altough since the mass of that third wall is much lower than the other two walls we may discuss if this is indeed a triple leaf or not)

Yes, that is the question Ineed answered before I start throwing layers of drywall on with $$ green glue...

why can't you do a normal outer leaf beef up and cut strips of sheetrock to fit in between the studs up against the rigid foam? you'll have to use ledgers to secure the drywall since you can't screw them into the rigid foam, maybe glue them to hold temporarily

I worry about the prospect of beefing up the foam insulation since it's so flimsy... Usually one would place a considerable amount of pressure upon the inner surface being beefed up, so it seems a rather delicate situation. Also, remember -- it's not the wimpiness that determines whether something is a leaf or not; rather, it's the material's tendency to prohibit the free movement/compression of air when the opposing leaf resonates/vibrates. This is why, for example, one must be careful not to use kraft paper on insulation that is not pressed firmly against a leaf on the side of the kraft. That may be kind of hard to follow, so I'll elaborate: if the air space between two leaves is divided by a thin sheet of paper, the paper acts as a middle leaf, splitting the air pocket into two halves, which has (in theory) an adverse effect on the entire assembly. That being said, sometimes third leaves are unavoidable (or the costs of eliminating it are too great). In that case, one compensates or lives with the shortcomings (or both). It's OK to wiggle around this -- just be aware of the inferiorities and the reasons for them so that you can be as effective and efficient as you can be when steering around them. :-) --Keith :mrgreen:

I thought about beefing it up someway, but I'm thinking of just working with what I got and making the best of it...meaning just two layers of 5/8" drywall with green glue on top of existing and praying that the rigid foam insulation and vinyl siding doesn't reproduce low frequencies very well.

i think the mass of the vinyl siding will be too low compared to the multiple layers of drywall inside the building to materially affect the low frequency TL. it may buzz and vibrate though as Sharward has pointed out so maybe you want to run some low frequency sounds while you try to feel for any excessive vibration of the vinyl siding.

if the air space between two leaves is divided by a thin sheet of paper, the paper acts as a middle leaf, splitting the air pocket into two halves, which has (in theory) an adverse effect on the entire assembly.

The question is can that thin sheet of paper be neglected or not ? I have no idea of an existant criteria in this matter and when can we neglect the third leaf effect

I appreciate everyone's input. I can't imagine that the outer 'third leaf' will create any resonance issues. I banged on it with my fist- it doesn't really resonate on it's own. On the other hand, if I bang my fist on the drywall, it resonates a great deal. The two layers of drywall with green glue should take care of that...

I think you might not really understand the characteristics of resonance and how it affects isolation. I'm pretty green on it myself... But here's a real-world example I live a few miles from an international airport, and we are (unfortunately) in the take-off flight path of most flights. When a plane is over our house at about 2,500 feet, the framed artwork on the wall behind our bed sometimes vibrates. What I find most interesting about it is that it continues to vibrate, even after the plane has passed and is leaving the area, such that I can barely hear the plane anymore. I don't know if it's the extreme high or extreme low end that's doing it, but it illustrates how something can resonate and become a source of sound, even though the sound that is exciting it cannot be heard or can barely be heard. (Heh -- there's a plane flying over my house as I'm typing this! :lol:) An inner leaf of 3 layers of 5/8" drywall with Green Glue, plus a generous air gap, plus another leaf of 3 layers of 5/8" drywall with Green Glue, is an excellent assembly. The thing I do worry about is the effect of that wimpy, rattly outer leaf. Go outside and lightly tap on that siding and you'll see how a small amount of movement can cause a lot of noise -- multiply that by all the siding panels and you get the picture of what could happen. I do hope for your sake that it doesn't happen if you move forward... I just hope you understand that you are taking a risk and need to be prepared for that possible outcome, and either be prepared to live with it or have a plan to address it if it does happen -- much like i have done with my third leaf. --Keith :mrgreen:

Well, maybe someone reading this has experience or knows of someone who has experience with this particular scenario and can provide some insight...I wouldn't know how to repair the problem after all this construction... I used to live in a townhouse where the wall ornaments rattled as a train was approaching and leaving...when the train wasn't audible...so I know what you mean. I have tested the isolation as is...I can hear low end through the walls, but no rattling...

I have tested the isolation as is...I can hear low end through the walls, but no rattling...

Fill in the air space with low density insulation Add even more mass to the interior walls