Soooooo . . what's the conclusion if any . . can I get away with the current construction?
You can get away with anything you want. For the most sound isolation possible with the materials you have planned to use, here it is in more detail.
Seal the outer wall if it isn't air tight already.
Forget one of the inner walls that you are planning to build. Sorry, but in terms of isolation the middle one that you have already framed is the preferred one to forget. Place all the wall material you were going to put on the two new walls on the one remaining wall.
If you want to do something to increase the mass of the outer wall, then put additional material against the fiberboard between the studs.
Regardless of which wall you decide to keep, fill the space with sound absorbing insulation.
Hey Mark you're getting some good tips around here . If I may just add: If you do decide to keep the outter wall and increase the mass of it, it would probably be easier to attach a new layer from the outside (over the fibreboard) instead of between the studs. that way you have something to screw the new layer into (ie. your studs).So are you leaving just the two walls you have now (outter and the built frame) or...??Is that inner frame (pictured) floating or...? If it's not you could still keep it and use the RC on it!?
I just did some quick calculations. With the fiberboard and vinyl on the ouside, 10" airgap, and 4 layers of gypsum on the inside, the STC is 59 with TL 23dB@50Hz. Assuming that the compound shifts the resonance frequency down half an octave, the STC will be in the mid 60s.
Changing the airgap to 15" doesn't affect the STC significantly but it does increase the LF TL by 3dB.
Andre . . tis very kind of you to check this out for me. What are you using to run the calculations? Are you putting the 4 drywall layers on the studs in my last photo?
I guess I could do that . . I am considering putting drywall between the outside studs first. Possibly putting Homasote 440 and then Drywall between the studs. I guess that's the only alternative. Sounds like I blew it on the studs.
The thing is . . what do people normally do with a separate building that already has external wall coverings (ie. siding and fiberboard). I feel like I am stuck to some degree. sigh . . .
I guess I could do that . . I am considering putting drywall between the outside studs first. Possibly putting Homasote 440 and then Drywall between the studs. I guess that's the only alternative. Sounds like I blew it on the studs.
Why the homasote? It is not as dense as gypsum. Put an extra layer of gypsum.
The thing is . . what do people normally do with a separate building that already has external wall coverings (ie. siding and fiberboard). I feel like I am stuck to some degree. sigh . .
Either a new exterior or exactly what we are writing about.
Ok cool . . well for shits and giggles, if I was to take down the vinyl siding, which ultimately I wil be doing for aestethics, what can be put on the outside? Drywall would not be tolerant of the weather even if covering with an additional barrier such as plastic and then ????
Also if I do put the drywall between the studs as you suggested, will I need to caulk that tightly between. And can I glue that to the fiberboard, or possibly tightly fit it and put some coarse thread screw through the drywall into the fiberboard?
Thanks again Andre . . I will sit down this evening and read the white paper you suggested. I am by trade an electical engineer, but this world of sound isolation is fairly new and most interesting. Thank God for people like you to go the extra mile and are willing to lend a hand. My son is outside right now putting up a temporary wall for the winter behind the garage doors as we have decided to close things up and focus on the existing building and make the addition in the spring.
I was thinking of putting liquid nails around the perimeter of the area where I will be adding the drywall to the interior and squeezing it into the crack between the studs and the fiberboard and then adding the second exterior layer with my viscoelastic material applied on top of that. Then I will use the new walls I put up with RC and 2 or three layers of drywall along with the visco material.
Here is what the building looks like and the foregone addition until spring.
thanks again . . I hope I can someday help out as well.
. If I may just add: If you do decide to keep the outter wall and increase the mass of it, it would probably be easier to attach a new layer from the outside (over the fibreboard) instead of between the studs. that way you have something to screw the new layer into (ie. your studs).So are you leaving just the two walls you have now (outter and the built frame) or...??Is that inner frame (pictured) floating or...? If it's not you could still keep it and use the RC on it!? 