Condensation/Vapor Barrier

Hi all, I've been building my garage studio for a while now and have followed Rod's book as closely as I can. I hope my question is straightforward enough and if I'm asking something that's been covered a bunch please forgive my inability to track the right info down... My walls are as follows: Concrete block --- 1" gap ---- 2x4 framing --- R25 Earthwool Insulation - RISC1 clips+hat channel --- 5/8" gypsum board --- green glue --- 5/8" gypsum board --- green glue --- 3/4" maple flooring (as a finish layer). My roof is : Ridge and soffit vented Standard shingle/tar paper/OSB --- 2" air gap --- 5/8" gypsum board --- green glue --- 5/8" gypsum board --- R38 Earthwool insulation --- RISC1 clips+hat channel --- 5/8" gypsum board --- green glue --- 5/8" gypsum board --- green glue --- 3/4" maple flooring (as a finish layer). So my question is around vapor + condensation forming between the outer leaf and inner leaves of my design... I'm not concerned with the uppermost roof layer as it's vented, but what should I do about the inner area (where the insulation is) ??? Do I try to seal up the concrete walls? Or add a vapor barrier? If so, where do I attach it? I feel a pit in my stomach having advanced to the drywall stage and now realizing that I may have caused myself untold troubles. My Earthwool is paper faced, so I assume that is a vapor barrier... If so, is it just a matter of which way it faces? In or out? Im in Nashville so we have (on average) 7 months at 72 or below and 5 above that topping out in the mid 90's generally. (climate change might *change* that in the future but if we're all going to die i dont think as many people will be making records)

Welcome to the forum! However, we need you to read the forum rules and fully fill out your profile. Also, it would be nice if you put your name at the bottom of your posts so we know your name.

I've been building my garage studio for a while now and have followed Rod's book as closely as I can.

Can you post your 3D model and calculations for us to review? How far along are you in "building" your garage? Is it a single room for mixing? Or jamming? or tracking? or what?

My walls are as follows: Concrete block --- 1" gap ---- 2x4 framing --- R25 Earthwool Insulation - RISC1 clips+hat channel --- 5/8" gypsum board --- green glue --- 5/8" gypsum board --- green glue --- 3/4" maple flooring (as a finish layer).

Ditch the clips and hat. Ditch your "finish layer" for now. Also, adding green glue is expensive. It is awesome. But you probably won't benefit much more by adding a second layer of it if you apply a healthy amount in the first layer. The reason I say to ditch your finish layer is because depending on what the room is used for, you don't entirely know what your walls or ceiling need for treatment devices.

My roof is : Ridge and soffit vented Standard shingle/tar paper/OSB --- 2" air gap --- 5/8" gypsum board --- green glue --- 5/8" gypsum board --- R38 Earthwool insulation --- RISC1 clips+hat channel --- 5/8" gypsum board --- green glue --- 5/8" gypsum board --- green glue --- 3/4" maple flooring (as a finish layer).

This makes no sense. You haven't described any roof truss or joists for your OSB sheathing or your RISC-1 clips to mount to! Also, if your room is fully decoupled, you don't need the clips and hat!

So my question is around vapor + condensation forming between the outer leaf and inner leaves of my design... I'm not concerned with the uppermost roof layer as it's vented, but what should I do about the inner area (where the insulation is) ??? Do I try to seal up the concrete walls? Or add a vapor barrier? If so, where do I attach it? I feel a pit in my stomach having advanced to the drywall stage and now realizing that I may have caused myself untold troubles. My Earthwool is paper faced, so I assume that is a vapor barrier... If so, is it just a matter of which way it faces? In or out? Im in Nashville so we have (on average) 7 months at 72 or below and 5 above that topping out in the mid 90's generally. (climate change might *change* that in the future but if we're all going to die i dont think as many people will be making records)

Simple. Put the barrier directly on (touching) the cold side of your inner leaf sheathing. Greg

Thanks Greg! I’ll fill out my profile, thanks for the heads up. So I get that my roof assembly etc are hard to understand - I had some help from one of the ‘gods’ of studio construction on that aspect... There are two layers of 5/8 Sheetrock with GG mounted into each rafter bay on 2x2’s - that way my ridge/soffit vent system works + meets code. The structure is basically decoupled but unfortunately because of what I had to work with it’s not completely decoupled, hence the clips and track. Which I won’t be ditching! We’re literally putting up Sheetrock next week so the vapor barrier help is much appreciated. In terms of your other suggestions - thank you. The one about GG especially May prove hugely useful. My ‘finish layer’ of maple is a large part of the studio aesthetic but point taken about tuning the room from there. The room is a live room, primarily for tracking of live bands. Best, - Ben

In terms of your other suggestions - thank you.

No problem. You have my opinion on how I feel you should be building your space so that it functions as you require. Please use this thread to post pictures of your progress so we can see how you make out and it will keep us up to speed in case you have more questions to ask the forum members! I look forward to your pictures! Greg

Gregwor wrote:

Simple. Put the barrier directly on (touching) the cold side of your inner leaf sheathing.

Wait a sec -- I've always thought vapor barriers should be on the warm side which in most climates is the innermost wall against the drywall. It shouldn't matter whether you have one leaf or two. A google search should confirm this. I found a quote from Rod here: http://johnlsayers.com/phpBB2/viewtopic.php?f=2&t=14795&start=0 In a properly insulated wall cavity a vapor retarder (polyethylene sheeting is NOT a vapor barrier) placed directly behind the drywall on the building interior (in cold climes) or directly behind the building sheathing (in hot climes) will never cause (or allow) a condition where vapor will condense in the sheet covering it. that sheet will be one with the space it is within - ans the relative humidity will be constant throughout (small variations in stratification that exist notwithstanding. Not trying to gotcha, I'm doing a build myself and already spent some time agonizing about placing drywall against my exterior wall w/o some kind of vapor barrier. After much research I finally went with unfaced insulation in the beefed up leaf and plan to use faced for the inner leaf - facing inward and touching the drywall. I'm also planning to ventilate the void space somehow. Now I am a little confused about how to handle this if I end up doing an inside out wall. I'm guessing, for an inner leaf it would be (from outside to inside): Normal: studs-insulation-vapor-drywall Inside out: drywall-vapor-studs-insulation (but maybe? vapor-drywall-studs-insulation) Didn't mean to hijack the thread, but I do think you got it backwards.

Didn't mean to hijack the thread, but I do think you got it backwards.

I believe you are not understanding what I wrote. The COLD side of the INNER leaf sheathing. That means that the barrier is against the INNER leaf drywall inside the cavity --- aka the cold side of the inner leaf sheathing. If you put it on the warm side of the inner leaf sheathing and it wasn't inside out, you'd have plastic all over the walls instead of nice looking paint. That would be silly. Does my comment make sense now? Greg

Ah yes, makes sense now, thanks. So for an inside out wall, would the barrier some how be attached to the drywall inside the air gap? Borrowing this drawing from John I suppose the 50mm insulation shown could be faced (facing the drywall).

The barrier has to be tight up against the drywall. So, you would fix the barrier to the drywall before standing the wall up. It should be really easy when the wall is lying on the floor :wink: Greg

Gregwor wrote:

The barrier has to be tight up against the drywall. So, you would fix the barrier to the drywall before standing the wall up. It should be really easy when the wall is lying on the floor :wink: Greg

Wouldn't it be better to put it between the studs before you put in the insulation? You will have a hard time to make a good airtight seal between the ceiling and the walls I think.

Wouldn't it be better to put it between the studs before you put in the insulation? You will have a hard time to make a good airtight seal between the ceiling and the walls I think.

It has to be on the COLD side of the inner leaf drywall. Also, the airtight seal between the ceiling and walls happen similar to how "normal" frost walls work where you sort of bag it. Greg