The right way to do a window between 2 inside-out walls?

Is this the correct way to do a window between two inside-out walls? I could not find any references for doing a window between two inside-out walls, only for normal walls, so I did a design myself, but I'd like to get a sanity check on this, to see if I'm on the right track, or maybe forgetting stuff. It is based on Rod's book design for windows, but modified for inside-out walls. I tried to make the SketchUp very detailed, and labeled everything with layers. Please take a look and let me know what you think.

Stuart - there is no difference between inside out walls and normal walls as far as window construction is concerned.

Thanks John! That's more or less what I figured. The only big difference I made here was to put the glass on the "other" side of the wall from the drywall, in order to get the greatest depth possible between panes. Does it make any difference to not have the glass in the same plane as the drywall? There is still plenty of mass around the glass, so I reckon it should be OK. The other thing that confused me a little is the "continuous rubber seal" that Rod mentions in his book: With normal construction, that is easy to do since it is held in place by the framing, but with an inside-out wall, there is no framing in the middle, between the two leaves, so I just figured it would be OK to extend the window frames into the gap a bit, and put the rubber seal around those extensions, sort of like a "sleeve" that seals them together. I plan to staple it in place and seal it tightly with caulk, all around. Will that work? Those were my two big concerns. Apart from that, it's almost identical to Rod's book, page 88. Are those two mods OK? Or should I do something else with the rubber seal? - Stuart - (PS. John, did you happen to see my question to you about your soffit design, here? : viewtopic.php?f=1&t=11122&p=98105&hilit=soffit%2C+behind+front+panel#p98105 ).

stuart, I think it depends on how thick your rubber seal will be. if it's 1-2mm you could route your "LR - Window - Frame" from the bottom (all around). then you can glue and staple the rubber (the red stuff :)directly onto the main frame and install your window frame on top of it: (the gypsum shouldn't also be flush with the main frame, like in my drawing) for additional seal-safety you could also put some sealant in this routed trace. I did it with all my trims on windows and doors, too ;) greetings, carsten

Thanks, Carsten! I considered that originally, and I reckon its the best idea, but I honestly can't figure out how I'd be able to do that in practice, due to the extremely limited space in there. I couldn't figure out any installation sequence that would let me get the rubber inserted in there, tucker between the frame and drywall, then glued, stapled and sealed, since there doesn't seem to be enough room to get my hands in there (around to the far side of the window frame). That's why I went with the idea of stapling it to an "extended" frame, and even then I'm not certain I'll be able to do that successfully.

for additional seal-safety you could also put some sealant in this routed trace. I did it with all my trims on windows and doors, too ;)

Cool idea! Thanks! I'll definitely incorporate that. Did you just fill that with a bead of caulk before putting the trim in place? Or did you put a strip of rubber / neoprene in there? - Stuart -

well... maybe I'm wrong but I think it's pretty easy. step 01: build your walls as planned. step 02: glue and staple your rubber seal on the frame step 03: according to the thickness of the rubber and the place on the main frame where the rubber sits route your window frame parts. step 04: install your window frame into the mainframe question is: will you install a.) the entire (pre build) frame or b.) piece after piece? if a. -> then your routing should go to the end of the lumber (don't know how to say it in english. the pic should clear it up). otherwise you cannot push your frame in the opening. the rubber seal will block the frame. or simply use smaller lumber (100mm instead of 143mm) b.) would be a lot easyer to build. first bottom and top frame and then left and right. and ready 8) --- yes. just a bead of caulk. carsten

Damn! Now why didn't I think of that???? Here I am, banging my head on the wall, trying to imagine how to get my hands in between the walls to put the rubber in, and there you go, showing me that I don't need to do that! It is actually a piece of cake to do it, right through the window opening. THANK YOU!!!! :) :) :yahoo: OK, you convinced me. Time to modify the SketchUp... :) - Stuart -

actually it's a different sequence Stuart. check this .skp file and scroll through the scenes.

john, I had in mind that your step sequence starts when my proposal ends. carsten

Thanks for the animation, John! Very useful! That's pretty much what I had in mind for the latter stages, but I'm more concerned about how to do the continuous rubber seal around the entire package (between the two frames) that Rod shows in his book, and which has to come in first, based on the method Carsten came up with. After that is in place, then I'll be following your build sequence for the rest of it. - Stuart -

Stuart, Maybe I didnt do it the right way, but at least it worked for me in the Drum room I've built. Basically I didnt bother with the rubber seal but I applied a reasonable amount of caulk before, during and after placing the glass. I dont have any weak points through the window and it isolates perfectly. Our 146 noise evaluation resulted "null" meaning the noise was less than the ambient noise outside. Basically what I did is after you finish your inner and outer framings (inside out), you place the inner stops, that can be a 1x2 strip or whatsoever. Then apply a NICE amount of caulk all over the perimeter for sealing any gaps.. then, apply some more caulk "over" the stop where the glass is gonna rest on. . Then place your glass (the caulk is gonna compress and seal completely). After you set your glass, apply some more caulk now between the glass and the window frame.. and place your outer stop (that can be another 1x2 strip, stained, or those "quarter rounds" that also look cool). It worked for me, i dont know if thats the right methor or not, but it worked my 0.2 cents

hola jbassino, it's not that kind of "seal" stuart is lookinig for. the "continous rubber seal" in rod's book is only meant for stopping dust (from the isolation) to trickle between the window panes and onto the nice black cloth. cheers, carsten

From stoping dust? I dont get that I guess... What dust? Fiberglass particles? Doesnt the inner stop acts as a barrier as well for that? I see the rubber seal for something like the glass is sitting "comfortably" over a flexible surface instead of the hard wood below... am i wrong? Or perhaps the rubber strip also provides much more sealing when the glass compress it against the stop, like for door rubber seals. but since this is a fixed window, i think the caulk provides the same function..

jbassino wrote:

What dust? Fiberglass particles?

yes. exactly. if you open and close a door a heavy pressure is buildup in between your walls 'cause it can't go out of this absolutely sealed cave. this pressure trys to find a way out but it can't. if your space between the window isn't sealed this pressure will also push the air through the cloth wrapped rigid insulation stuff and therefore it's just a question of time that small particles may be pushed through the cloth and right between the windows... the windows should sit on glazing blocks. carsten

quote from rod's book: build it like the pros. page 87 on the bottom, last stanza: "[...] through the use of a rubber seal surrounding the opening between the window frames (which I use to keep dust from settling into the window opening over time and also to increase the effect of the air spring within the window panels themselves) [...]" carsten

Yep, that's the seal I'm talking about, Carsten! The continuous rubber "sleeve" that joins the two independent frames across the air gap, and keeps out the dust. I don't plan to take out those windows every few months to clean them! Rod didn't mention it, but I guess it will also help to keep out humidity, and therefore condensation on the glass. Yes, I'll be putting plenty of silica gel beads in there, but they only have a limited capacity for absorbing moisture, so I'd lie to keep humidity out of there as well. Basically, I want the entire air gap between the windows to be totally sealed off from the rest of the air gap between the leaves. - Stuart -

I don't see any point in the rubber - the soft fiberboard stops any dust.

Stuart, As far as Im concerned, you don't get condensation problems with windows on a MSM system. That only applies when puting two windows on the same leaf (lets say a thick brickwall wall) so there you might have condensation issues due to different temperatures and pressures between the air cavity and the exterior. And thanks for the clarification Carsten, now I see your point. But like John said, the fiberboard will stop the dust, and even a closed cloth will do as well, unless you use a really thin, open cloth. You could even use EPS covered with cloth

jbassino wrote:

Stuart, As far as Im concerned, you don't get condensation problems with windows on a MSM system. That only applies when puting two windows on the same leaf (lets say a thick brickwall wall) so there you might have condensation issues due to different temperatures and pressures between the air cavity and the exterior.

This is correct for the most part. As long as the temperature is the same on both sides of the glass, that is, the environment is static from one room to the other, then you will not have any issues with condensation. Glass is a barrier so vapor can be extracted from the air (H2O) between the two pieces if the temperature where allowed to moderate on different sides.

The other day I was recording vocals and it was a very sunny and hot day, almost hell outside. Due that I havent installed AC yet in the vocal room (just fresh air supply), the room was VERY hot because air from the outside (hot) was going inside the booth plus the heat from the singer as well. However, In my control room, I've got the AC running pretty cold. End of story, each room with extreme temperatures and no condensation or whatsoever inside the window :)

I don't see any point in the rubber - the soft fiberboard stops any dust.

Assuming you can actually get soft fiberboard here in Chile! I have my doubts... I know Javier looked for it for a long time for his hangers, and if I recall correctly, he didn't find it. So I was going on Rod's plan, which calls for "Fabric-wrapped rigid fiberglass" and "fiberglass over continuous rubber seal". As Carsten pointed out, opening and closing doors can cause some pretty major pressure changes inside the walls, so I guess that's why Rod recommends the rubber seal: Even with fabric-wrapped 703 you could conceivably get dust coming through, surely? - Stuart -

Stuart, Why don't you spray some kind of sealant (Laca?) under the surface of the cloth, so you seal completely any micro-gap between the cloth cells, that way its impossible for dust to pass through My guess! Just to avoid an unnecessary headache :D Also, check www.textinsa.cl out (I bought the cloth there..), They provide beautifull cloths and most of them have very closed weavings as well

Stuart, Why don't you spray some kind of sealant (Laca?) under the surface of the cloth, so you seal completely any micro-gap between the cloth cells, that way its impossible for dust to pass through

Cool idea! Yeah, that should work, I reckon. Much easier than the rubber sleeve. Thanks for the tip! Thanks also for the "dato" about the fabric guys. - Stuart -

jbassino wrote:

The other day I was recording vocals and it was a very sunny and hot day, almost hell outside. Due that I havent installed AC yet in the vocal room (just fresh air supply), the room was VERY hot because air from the outside (hot) was going inside the booth plus the heat from the singer as well. However, In my control room, I've got the AC running pretty cold. End of story, each room with extreme temperatures and no condensation or whatsoever inside the window :)

Forgive me if that seemed like I was correcting you. I was not. Still, a simple test like you describe is not enough to define if or not moisture will collect in this manner. But this is a good example of what you do not want to do on a regular basis. It is not a matter of if, but when.