John Sayers' Recording Studio Design Forum Archive

Based on the left bank experience - do you think it would make sense to add a layer of drywall on the inside face of the external wall? I was assuming that this would create 3 masses & so be worse.

I have wondered if my external wall will have enough mass. Right now it's just 1 layer of OSB covered in polystyrene (which will have no STC value) and then eventually siding. I have been looking for something with mass to increase the mass of the external wall. I've had an idea of putting (& sealing) roofing felt tiles over the OSB on the inside of the extermal wall between the studs. This stuff is remarkably heavy given that it has rock in it & it's dirt cheap - about $10 for one pack that is tough to lift. Does that sound like a winner? It would be easy to staple between the studs & seal it with roofing tar - which is also dirt cheap.

Based on the left bank experience I would add it Andrew........yeah - I know - It's three layers and two air spaces.

cheers
john

Get a sample of what you intend to use - light up your propane torch and try to burn it. If you succeed, either use something else or take out a $5 million policy with ME as the beneficiary...

You could use 5/8" firecode gypsum board in sort of the same way, adding it between framing members and thoroughly caulking.

John, I think your assessment of Left Bank's success is correct - that's why I was trying to get Michael to put absorptive stuff around his door from the drum room... Steve

The fire aspect is a good point - I tried the burn test & yes it would heartly support combustion - but heck if the place is going to burn down it's going to burn down no matter what you have in the walls. I plan to have those external walls filled with spray in foam - which is fairly combustible. Covering the external wall with drywall should provide the firestop.

One thought about the effectiveness of the inside out wall - could the fact of gluing the insulation to the drywall be one of the contributing beneficial factors? This would allow vibrations in the wall from low end to transfer to the insulation more readily and convert to heat - rather than packed in insulation - which would be vibrated by air instead of the wall itself. Just a theory - bearing in mind that have no clue what I'm talking about

"heck if the place is going to burn down it's going to burn down no matter what you have in the walls" - NOT SO.

If you use steel studs, firecore wallboard, flame retardent cloth, and concrete shells you can build an almost entirely incombustible shell. And, considering how closed a system you have in a tightly built studio, it SHOULD be as incombustible as you can make it.

I might be as non-chalant as several other posters I've answered, except for this: Have you ever seen a marshmallow that spent too much time over the fire? Remember how the black part just sort of "slid off" the gooey insides? Well, I've had the dubious pleasure of seeing that very thing, only with HUMANS - two of them, both of whom lived long enough to scream for someone to kill them. They were both working in a rare metals plant, shoveling metal chips, when something got just a little too hot. The Zirconium chips they were working with are the same metal that is rolled thin and cut in fine slivers to make FLASH BULBS for cameras. Only this "flash bulb" was a room about 20 feet square.

It took about 10 years before I could sleep thru the night without nightmares - gee, I wonder why I'm concerned about flammability...

Anyway, about the glued on insulation - I don't think so. The conversion to heat is caused by the AIR molecules trying to move back and forth thru the interstices of the insulation and meeting resistance. The more resistance, the more conversion, that's why denser material absorbs more.

Sorry about the soapbox - every once in a while I still get flashbacks and it scares the shit out of me. When I'm scared I either go away or blather... Steve

Point well taken about the fire issue - will re-think that addition.

If you're looking for a good wall that's still safe, I'd use two layers of 5/8" firecode sheet rock glued between the studs and up against the outer sheath, as you mentioned - then, if you have the room I'd add 2x2's (drilled, glued and screwed) to each stud on the inside, in order to increase the air space -

put 3-4" of Rockwool (3 lb/cu ft is best performance) in between the studs, held in with the SMALL mesh chicken wire available (at least in more rural areas) at farm/home supply places - staple the chicken wire onto the studs being careful to only staple the wire where two strands of wire are twisted together (won't break that way)

Then, put Resilient Channel (RC-1) over the stud extensions horizontally on 16" centers (The bottom piece goes on with the "flapping" part UP, so you can screw to it) Add two layers of 5/8 firecode sheet rock, making sure that the rock does NOT touch the floor (use 1/4" spacers while fastening, then pull the spacers and caulk with Silicone or Butyl NON-HARDENING caulk (or US Gypsum's Acoustic Caulk if you're lucky enough to find it) If you want to add a center layer of sound board as well, fine. You will most likely want to put the RC on 12" centers with 3 layers - and be sure to mark floor and ceiling temporarily where the studs are, so you don't "short out" the RC with a screw when installing wall board.

When using more than one layer of sheet rock in a wall leaf, do NOT glue the two layers together - performance is better if they can flex independently, as long as they're not separated by an air space. Never line up seams from one layer to the next.

Once you have all that in place, you could still put whatever wall treatment you want, wherever you want... Steve

Thanks. I re-tried the burn test & although the stuff melts & flames when the blowtorch is on it - as soon as you take off the blowtorch the flame dies instantly - so perhaps it isn't so combustable or at least no more than the OSB sheathing. The stuff is owens corning mineral loaded felt. It's about half the weight of mass loaded vinyl and only costs $13 per 108sqft roll. For $200 I can put 2 layers between all the studs - so I think it's a winner for adding some mass to the extermal wall.

I need to do the double wall construction so I can make the internal layout. So, my wall will be

OSB + 2 layers of this heavy felt stuff between the studs (the studs are already well caulked) + foam filled (I'm getting the peaked roof between the roof studs filled with spray in polyurethane foam so the walls is just a bit extra) + 1 layer of drywall

Then the 2nd wall - the inside out wall - fiberglass + 2 layers dryrock then the studs.

I'm thinking if I can make the external wall as solid as possible (no air) then it'll still only be 2 masses and 1 air gap - which fingers crossed - should work.