Bizarre Wall Sandwich w/Pics: Quick advise needed

I'm in a situation where I have a 25x11 garage available to me to turn into a recording studio. The garage is detached from the house and was probably built in the30's or 40's but was rebuilt/remodeled as a video edit room about 5 years ago. The guy who did the rebuilding was a hack to say the least. Air tight, plumb and level were not in this guys vocabulary. So needles to say it leaves some things to be desired, but it has good electric, existing cables, and it's in a good location in Hollywood. Isolation wise, much improvement could be made. The structure is almost “good enough” for normal control room volumes and most instruments other then acoustic drums. However, drums are loud outside and need to be contained to not run into problems with the neighbors 20' away. To save money, the leading plan so far is to divide the room up and make a 9x11 drum iso room. The plan was to to do the mass-air-mass 2 independent wall 2 leaf system just for the 9x11 “live room”. Well, at least that was the plan until I ripped into the wall and found out that there is NO external wall other then the siding! The Wall Sandwich break down: -Exterior fiber cement siding (poorly installed AKA-not air tight-caulked only in spots) -Black tar paper (No actual exterior wall!!) -92mm Steel studs (with original wood studs AND the new steel studs quasi-staggered pattern it appears. For example it looks like the tarpaper/siding is in contact with both types of studs, while the interior drywall is only in contact with the wider 92mm steel stud. I hope that makes sense!) -4” Johns Manville “Thermal and Sound Control” (with paper backing “mostly” toward interior wall) -Steel mesh fence (P.I.T.A!!!) -2 layers of 5/8” Drywall The Ceiling on the interior is vaulted (81”' to 104”) and looks to consist of: -Exterior shingled roof -4” Johns Manville “Thermal and Sound Control” (with paper backing toward interior drywall) -1 layer 5/8” Drywall The Floor: -Laminate over concrete slab Due to the difficult shape of the ceiling and the steel mesh in the internal walls, I want to avoid ripping out the existing 2 layers of drywall if at all possible….or at least make it the last resort. Thus the Options: 1. Rip off the siding and put “beef” on the exterior of the steel studs where there is ONLY black tar paper now. Leaving the interior wall as is. 2. Build a “room within a room” on the inside and make the new wall air tight and lined with mineral wool. This would create the dreaded third leaf effect unfortunately. The question is would the tar paper and poorly installed siding be so leaky and wimpy as to not be TOO much of a problem as a third leaf? 3. Suck it up and realize that it's going to be more trouble then it's worth and save up for a long time to build a new free standing isolated drum room from the ground up. Please tell me if more information is needed, and I’ll do everything I can to get that info. Thanks!

I'm rushing out the door, but I wanted to give you a quick "welcome" and some preliminary thoughts. Since you appear to be williing to rip the siding down and put on the exterior face of the studs some plywood/OSB, that would be a good start. I would think two layers of plywood/OSB with some Green Glue sandwiched between would be great! I wonder if you could try to salvage the siding so that you could reuse it when the sheathing is installed...? The windows, though... :? ...Those are going to be an issue. And the roof, oy, I don't know... Not in an enviable position are you! :roll: Other thoughts welcome... as always... --Keith :mrgreen:

2. Build a “room within a room” on the inside and make the new wall air tight and lined with mineral wool. This would create the dreaded third leaf effect unfortunately. The question is would the tar paper and poorly installed siding be so leaky and wimpy as to not be TOO much of a problem as a third leaf?

I wouldn't classify the siding/tar paper as a leaf. I'd go with room within a room as you suggested. cheers john

Why isn't the siding considered a leaf? It's leaky, I'm sure, but not exactly "ventilated." Wouldn't it be prone to resonance being so relatively close to the inner drywall middle leaf, especially at the pesky low end of a drum kit that he's most concerned about? --Keith :mrgreen:

Keith and John, thank you both very much for the quick responses. I would definitely prefer to go with the room within a room option: -it would give me 2 discrete decoupled walls -it would allow me to really “know” everything on the inside was air tight -not throw off the exterior geometry relationship due to the added thickness of the extra sheathing -allow me to work in AC instead of the relentless sun! So I'm going to take my chances with that option and I'll report back how it performs so others can learn from it. By the way Keith, the windows are in the control room end of the building. The drum iso room has no windows at all, and I have 2 heavy fire doors that I scavenged from a local hospital remodel. If anyone has any ideas about the ceiling , please pipe in! I have a feeling I'll be ripping the existing ceiling down mainly to rebuild a decoupled version, although I haven't figured this out yet. Two quick final questions to get me officially rolling: 1.Should I replace the 4” Johns Manville fluffy with mineral wool in the ceiling, or use both (there's enough room)? OR is the existing Johns Manville good enough? 2.Considering I'm going with the internal build, should I caulk the outside siding and seal it up, or should I run something under the edges to break what is there of the existing caulk to make it breath/leak better to minimize the the theoretical third leaf effect?

delusion wrote:

1.Should I replace the 4” Johns Manville fluffy with mineral wool in the ceiling, or use both (there's enough room)? OR is the existing Johns Manville good enough?

Adding fluffy would not be a bad thing - but for all intent and purpose - any improvement mineral wool is so marginal ((at best) (if at all)) that it doesn't make any sense to pay extra moinies for it........ Hoever - I would add to what's there - at least another 12"

2.Considering I'm going with the internal build, should I caulk the outside siding and seal it up, or should I run something under the edges to break what is there of the existing caulk to make it breath/leak better to minimize the the theoretical third leaf effect?

It is already a 3rd leaf........... and it will act in that manner - the amount of air leaks you are talking abuout are minimal compared to the overall - But - in your case I think this is one of those times where I would not remove the inner face - as a matter of fact I would add to it - and then build my new wall in front of it. I see it as being next to impossible to do any sort of a good job adding mass out at the outer face - so live with it and move on to get the best that you can. Rod

Thanks Rod, I'm reading your book as we speak. The readability of it is very well done considering the highly technical subject matter. I'm going to do as you suggested and add one more layer of drywall to the existing walls. I just want to make sure that using green glue to add on to an already painted wall is not going to be problematic. Please advise if so. Thanks again!

delusion wrote:

I just want to make sure that using green glue to add on to an already painted wall is not going to be problematic. Please advise if so.

Delusion, I can't see how it would be a problm - BUT - for the cost of green glue I woulnd't go by mine (or anyone elses) guess...... Call the manufacturer and ask them the question. They might tell you to scuff up the finish first - or that in order to gaurantee success that you must first prime the surface with BinSeal - Kilz or Bulls Eye Shellac. you won't know until you call. Rod

And when you call, let us know what they say about it! :-) --Keith :mrgreen:

Just called the green glue company and was told that there would be no problem using it with an already painted surface.

Ok guys, minor demolition, floor repair, and more planning (a/c, electric, etc.) progress has been made. Unless someone stops me, I'm probably going with the space saving internal wall design found here, but with a little wider air gap & extra drywall & green glue: http://www.saecollege.de/reference_mate ... /Walls.htm Seeing as though the room will be small, I'm going with the dead absorbent setup in there and will add convolution reverb with altiverb to compensate. Not ideal, but seems like the best option considering the circumstances. I am in the middle of getting to grips with sketch up, and will be posting my overall plan for you guys to correct or enhance very shortly (probably in another thread). My main concern now is still the ceiling/roof. As you can see in the pics, the ceiling is vaulted. This is posing quite the challenge for me. If I just went with a flat lower ceiling, it would be a lot easier, but the the ceiling would simply be far too low for overhead drum mics I would think (81”)....but maybe the fully absorbent ceiling would make comb filtering a non-issue. Please share your experiences here if this is a possibility. I have been researching like crazy, and am wondering about the third leaf effect of the roof itself. The roof planks themselves are not the best. they are old and have noticeable gaps between them. None-the-less the roof does not leak water. The kicker here though is that the roof is NOT vented in anyway that I can tell, so from what I understand, it will act as a wimpy but true leaf. Beefing up inner roof from inside looks next to impossible due to the different eras of construction that are tied in together. So the questions/options are: 1.Build a new ceiling that is parallel and just below the existing vaulted drywall ceiling? This new ceiling would be supported by the new inner walls... 2.Build the same shape ceiling as above, but suspended with RC or isolation hangers from existing studs instead? 3.(Warning I may be insane) Rip off the roof shingles and beef up from the outside, and then use one of the above options sans the 2nd internal ceiling. If anything I propose is just overkill relative to the rest of the plan, please let me know.

Ok, somebody stop me, if I'm about to make a mistake. The internal ceiling goes almost completely to the roof, so there really isn't much “attic” space at all. Due to the ho-hum condition of the existing orginal roof wood, it's looking like taking the shingles off and replacing the old wood with more beef and putting the shingles back on will actually be easier then dealing with all of the obstacles on the inside. The way I see it, using the roof itself as the outer leaf will avoid the 3rd leaf AND give more headroom on the inside because we can keep the ceiling higher. The roof is currently NOT vented in anyway. Will I run into any problems sealing it up as planned and having no vent, seeing is though I live in southern California where it never snows, hardly ever rains, and even in the winter doesn't get that cold? I understand how busy everyone is, but if I could get just a “Plan seems OK” or “Halt all progress now, and I'll tell you why later” response, I would be very grateful!