Sealing an Inside-out Wall

Hello all, I've been reading this forum for quite a while, and i'm still amazed at the amount of info there is in here, and for free! so first i'd like to start by thanking all the contributors here! I'm aiming at building a basement home studio and right now i'm in the phase of "learning as much as i can before i do anything stupid". which means i'm afraid i'm gonna ask a lot of silly questions in the coming months but i guess this is more or less the only way to learn. I have read about the inside-out wall construction designed by John in his manual, and i keep asking myself the same question: how do you seal such a construction air-tight? With a conventional stud wall, you are facing the gypsum plates and you connect all the wall/floor/cealing sections with acoustic sealant to make the room airtight. In an inside out wall that would'nt work as i understand. so, how do you get the room air tight? Florent

I say, first build your frame on the floor, and do all the sealing stuff, then get some people in and put it up.... that how I would do it.

John says it's pretty simple really.

thanks to you both! i ran quite a few search over the forum before asking the question but i didn't find the thread adam mentioned. so all the sealing is done on the inside of the room, caulking the wall frames where they meet the gypsum / floor boards / ceiling panels. that means a lot of caulking:), do i have to use an acoustic sealant (i.e some kind of acrylic caulk that will keep its elasticity) for all of this or can i go with some cheap latex that will harden with time? i read the stickies on caulking, but couldnt figure out which type to use on different parts of the room, and given the difference in price, it's worth asking! Florent

john, thanks for reposting the figures! i guess it is the first drawing that should be used when doing an inside out wall, right? the only difference is that the isolation is glued to the outward facing side of the gypsum boards.

the only difference is that the isolation is glued to the outward facing side of the gypsum boards.

I don't see that on John's diagram, and I doubt that gluing insulation to drywall is a good idea anyway. Just lay the insulation in the cavity freely. It doesn't need gluing. - Stuart -

Hi stuart, now i'm a little confused. if one look at the recording manual, it says that in an inside out wall, the insulation is glued to the plasterboards, and that the cavities are left empty for treatment (http://johnlsayers.com/Recmanual/Titles/Acoustics3.htm). is there an alternative to gluing if you build inside-out walls? Florent

Perhaps you linked to the wrong page in John's old manual? The page you linked to is about normal construction, not inside-out construction, and nowhere does it mention "gluing insulation to drywall". In fact, the only mention it makes of gluing at all is this: "The options are: * Adding another layer of gypsum which is glued (not nailed) to the first sheet ...". But there is nothing at all about gluing insulation to drywall on that page. And there is also nothing about inside-out walls on that page. It also says nothing about "the cavities are left empty for treatment". In fact, it clearly shows the cavities between the two leaves being filled on both sides with insulation, and later studies (that came years after John originally wrote that manual) show that taking this even further by filling the entire cavity with insulaiton, increases isolation eave more. Perhaps you are confusing the cavity inside the wall ("the "S" part of the MSM equation) with the space between the studs on an inside-out wall, which also usually has some form of insulation in it, as part of the room treatment? Isolation and treatment are two entirely different things. - Stuart -

Stuart, maybe Florent meant that 50mm insulation glued to the drywall layer at the back of the inside-out wall. see picture and also what John wrote about it: "This system halves the thickness of the wall (100mm(4") instead of 200mm(8")) and makes the 95mm(4") cavity in the wall available for acoustic treatment. (Slat resonator depicted in drawing) Construction requires building the wall panels on the floor, applying the outer cladding and gluing the insulation to it then standing the wall panels up into place. You end up with a wall with the cladding on the outside and a 100mm (4") cavity for internal acoustic treatment. Obviously the panels must be sealed when connected to each other and if you are using a double or triple layer you can seal it like this." -janne

stuart, sorry, it was the wrong link indeed. i just copied what stood in the URL field of firefox but did not realised that it was a frame page. here is the correct url http://johnlsayers.com/Recmanual/Pages/Walls.htm janne, this is the paragraph i was talking about.

Stuart, maybe Florent meant that 50mm insulation glued to the drywall layer at the back of the inside-out wall.

That's what I assumed he meant. You can do either - you can glue it to the back of the frame, or you can attach it to the outer wall before you stand up the frame. check out this page viewtopic.php?f=11&t=6968&start=15