Wood Shop wrk area Vapor & Moisture Barrier Question

[SpiderDave]

I'm building a work space in my shop to keep the dust out and the heat in the rest of the shop. 2 walls are exterior and 2 are interior. I have a 2,800 cfm dust collection that'll be used in this area. I do have heat in both the shop and this work area too. I keep it around 38-40* ( keep plumbing safe) when i'm not around in the winter. When I'm out there, it's gradually bumped up 10*-15* to make it comfortable enough for me to work.  The outside is metal siding - insulated pole barn with concrete floor. 

One exterior wall of this room is insulated with r-31 fiberglass insulation, has roofing felt (asphalt?) paper over the pole barn structure under the metal siding. Insulted with r-31 and 1/2" OSB sheet on the inside wall with sheetrock over that and no vapor barrier that I can find. This wall is different than the other walls for some reason, but never had any issues yet.

The second exterior wall has plywood and also with metal over it. I think there is Tyvek under it, where I've seen. Has R-31 insulation, 1/2" OSB sheets on interior up to 8ft, and no interior vapor barrier. 

The last 2 walls are the interior walls which have R-31, sheeted with 1/2" OSB. 

My concern is moisture in whatever form it takes turning into condensation. Especially here in Oregon where mold is the leading cause of damage or usually linked to it somehow.  I was imagining the Dust Collector in the winter pulling all that cold moist air through the open vent in the wall. And then rapidly dropping the room temperature, creating condensation. Our winters average 20's-30's, and can vary either way at times. 3 seasons out of the year, humidity is always an issue. We're up in mountains a bit too, so it can be cooler on average. Mold, slime, fungus. mildew and moss on both buildings and landscaping are a constant battle. 

Anyway, The interior walls will likely already be warm from the shop when that DC unit's turned on. And here comes all the cold air rushing in. The one wall that has been done with sheetrock and roofing paper on the exterior. I'd like to paint it with some oil base paint to make it more of a vapor barrier rather than tare it all out. Is that a bad idea? My concern is trapping moisture inside the exterior walls with a roll of poly stapled on whether I paint that one wall or not. I haven't had problems inside the walls yet. But until now they will have never been very air tight before, either. They've always been able to breath and dry out before. I'm going to caulk and foam seal everything I can find along the way. I haven't found it in the walls yet. But crazy enough my rafters and joists get black mold occasionally. Much less since I started heating. I clean and kill it inspecting everything once or twice a year,..its a pain. So it worries me.

Okay before I ramble on and mix anybody up here - hopefully this made sense enough. Is that asphalt felt paper on the one ext. wall going to be an issue? Should I Vapor Barrier every wall on the inside, or just the two exterior walls? Is it acceptable to put the barrier sandwiched between the OSB and sheetrock if I do it, or behind the OSB (both)? no doubt most of the wood workers here have a Dust Collectors and work areas. So, I was hoping maybe we could debate on how to handle this build with the knowledge of someone who's done it before? Or came across the same issues? Even if you haven't, I'd still like to hear your opinion if you can spare it. Any help would be greatly appreciated so I don't do more harm than good here. Thanks ALL for reading! Have a good one!!

[jasfrank]

If your exterior side of the walls has a vapor barrier don’t put one on the inside walls. That would trap moisture inside the wall. I would consider asphalt paper to be a barrier.

[MstrCarpenter]

If your exterior side of the walls has a vapor barrier don’t put one on the inside walls. That would trap moisture inside the wall. I would consider asphalt paper to be a barrier.

I agree. As a rule there should only be one vapor barrier. The vapor it restricts is moisture vapor. We install these barriers to reduce the chance of that moisture vapor condensing when it meets colder air or surfaces. You are asking for mold if you install two vapor barriers. If kraft faced insulation is used, an additional vapor barrier should not be installed. If it's absolutely necessary, the paper should be sliced/shredded to allow cooler air to temper a bit before coming in contact with the warm inner wall surface and to create an easier path for moisture vapor to the exterior, where hopefully there is only an air infiltration barrier. (They're designed to allow moisture vapor to pass thru.)

In southern climates it's usually warmer with higher humidity outside; so where should the vapor barrier go? That's an ongoing debate that luckily needn't be addressed now. However, on your second question; in my opinion, your interior partitions do not require any vapor barrier, and I wouldn't go crazy making them air tight either. Put all your efforts into making the shell air-tight; R value doesn't matter if there's air flow.

[daddo]

I've never done this in a shop, but it would be interesting to see how a makeup air duct system would work. Along side of the collection duct, have a outside air duct next to it as to circulate the air at the collection site, thus preventing outside air distribution into the entire room.

 Another might be to run the outside air duct through the/a heater to heat the entering outside fresh air, and have a possible condensation trap.

Or more easily, do away with using outside makeup air and just recirculate the DC air since it is filtered to microns anyway.

[SpiderDave]

I agree. As a rule there should only be one vapor barrier. The vapor it restricts is moisture vapor. We install these barriers to reduce the chance of that moisture vapor condensing when it meets colder air or surfaces. You are asking for mold if you install two vapor barriers. If kraft faced insulation is used, an additional vapor barrier should not be installed. If it's absolutely necessary, the paper should be sliced/shredded to allow cooler air to temper a bit before coming in contact with the warm inner wall surface and to create an easier path for moisture vapor to the exterior, where hopefully there is only an air infiltration barrier. (They're designed to allow moisture vapor to pass thru.)

In southern climates it's usually warmer with higher humidity outside; so where should the vapor barrier go? That's an ongoing debate that luckily needn't be addressed now. However, on your second question; in my opinion, your interior partitions do not require any vapor barrier, and I wouldn't go crazy making them air tight either. Put all your efforts into making the shell air-tight; R value doesn't matter if there's air flow.

Sigh,.. Looks like I'm going to be tearing some sheetrock out soon. Heh. The insulation behind it all is kraft faced unfortunately. This building's had a lot of different hands in it. I'm getting it all straightened, out as I go. The insulation with kraft facing was my doing. It originally had kraft faced 2x4 r-11 in it with OSB over that. It looked good inside so I didn't question anything, just took care of a few issues while I was in there. Then upgraded the insulation with 2x6 r-31. I was glad to just get it done and move on to the next - because of all the hiccups I've encountered along the way. 

For the sake of myself understanding clearly. I do plan on heating this smaller room from time to time when the shop is previously colder, instead of the whole shop. Since the cold and warm sides will be randomly switching. Just makin' sure.

I've been insulating everything because I'm trying to reduce as much noise escaping as possible. That's why the interior walls are insulated now. Same goes for the layer of fire rated sheetrock. Which will also protect the OSB from welding sparks. It was cheaper than roofing and withstands more than I'll being throwing at it anyway. 

Thank you so much!!

[SpiderDave]

I've never done this in a shop, but it would be interesting to see how a makeup air duct system would work. Along side of the collection duct, have a outside air duct next to it as to circulate the air at the collection site, thus preventing outside air distribution into the entire room.

 Another might be to run the outside air duct through the/a heater to heat the entering outside fresh air, and have a possible condensation trap.

Or more easily, do away with using outside makeup air and just recirculate the DC air since it is filtered to microns anyway.

Heck yah, If you had an in and an out hose connection and some sort of self contained dust collection built into each machine, that would greatly reduce the amount of shop air removed. Certainly no simple task. One of those things you do, just to see IF you could do it. ha! But yur right, investing in a really great filter system would be the way to go for sure. It's on my bucket list. 

For now, I'm piping it outside after the cyclone and bringing fresh air in from the other side. Fits my budget at the moment. Nothing visible will be coming out of that exhaust pipe. And I live kind of in the country edges with minimal neighbors. So, I'm lucky there.

[MstrCarpenter]

Sigh,.. Looks like I'm going to be tearing some sheetrock out soon. Heh. The insulation behind it all is kraft faced unfortunately. ...
Thank you so much!!

I don't think I would worry about using a moisture barrier paint (Which by the way, will meet code requirements) or any paint for that matter. When I cautioned about using poly over Kraft faced, I was referring to stapling poly to the studs; right against the tar coated Kraft paper. I have frequently seen thick black mold between them. We never put a vapor barrier on ceilings, but cathedral ceilings, more often than not, get Kraft faced and don't cause any problem. So, moisture condensing on your insulation or in your walls is bad, but it's going to happen at times. Not letting the moisture get out is real bad, and will only get worse because the R-value decreases as insulation gets wetter. Just keep sealing and caulking to stop the airflow and you'll be greatly reducing the amount of moisture that gets in the wall in the first place.

[SpiderDave]

I don't think I would worry about using a moisture barrier paint (Which by the way, will meet code requirements) or any paint for that matter. When I cautioned about using poly over Kraft faced, I was referring to stapling poly to the studs; right against the tar coated Kraft paper. I have frequently seen thick black mold between them. We never put a vapor barrier on ceilings, but cathedral ceilings, more often than not, get Kraft faced and don't cause any problem. So, moisture condensing on your insulation or in your walls is bad, but it's going to happen at times. Not letting the moisture get out is real bad, and will only get worse because the R-value decreases as insulation gets wetter. Just keep sealing and caulking to stop the airflow and you'll be greatly reducing the amount of moisture that gets in the wall in the first place.

Thanks MastrCarpenter, I really appreciate the patience and help - from everyone. I just want to get this right considering the mold issues with this structure. I've been researching extra hard on this and becoming more eduacted, a bit more confused and worried than when I started frankly. I may be chasing my tail a little bit here, but I 'will' end up with something I feel good about. If I sound a bit thick, I apologize. Ha!

You know, I've seen that black mold behind the karft paper you're talking about when removing some of the old insulation. And it had nothing over it at all. The places I've seen it the most is where it wasn't sheeted over. Just stapled and exposed above the OSB sheets reach. Is that the cold from outside conducting through the stud and hitting the inside air? When I've removed OSB, I don't  see any between there, not that I noticed I should say. Maybe because there's little to no air space and colder air's trapped there that doesn't meet the warmer air?  

So far I think havng to remove the OSB & Sheetrock, then putting up interior poly, and re-sheet is the right move for the exterior walls is the majority vote here? Does that sound right? I'm not disagreeing at all here, just asking because I'm just nervous about putting poly on a wall that's inherently damp to begin with. But I'm absolutely willing to do it, if it's the right thing to do - no matter what 'I' think. This walls never been closed up so tightly before, so I'm nervous after all the other things I've wrong with this shop. Tired of chasing problems with this building. Wondering if I'm makin' it better or worse?

If I go with the poly, would putting soffit vents along the lower wall kinda throw a monkey wrench into the poly's function? That was my original plan to get air to the main posts which are in the ground and whatever moisture comes up through the concrete. I know the wall will be able to breathe slowly from the outside, as Roofing Felt is a vapor retardant, not a barrier. And so is Kraft backing of insulation from what I've learned. But will that be enough escaping with the moisture coming from below? That's assuming I never get additional moisture in the wall from a leak someday. I can't help but wonder if leaving it as it is might be okay?? The kraft may slow the vapor down enough to prevent condensation, but allow moisture to escape over time? I did tape up pretty tight. 

A surprising number of people have told me to leave it as it is because the roofing felt is slow to allow moisture to escape and you don't want to double up the barriers any more there, so it's fine. But more have said to re-do it. To cut and slit the kraft and then use poly sheet under the OSB and sheetrock. I wish I would've set up some kind of vote on this to see the over all opinions - out of curiosity. If I do go with the poly behind the OSB & Sheetrock. Should I remove the stud over lap from the Kraft on the insulation also. to avoid the black mold issue you say you've seen? Or would it make a difference?

[SpiderDave]

I don't think I would worry about using a moisture barrier paint (Which by the way, will meet code requirements) or any paint for that matter. When I cautioned about using poly over Kraft faced, I was referring to stapling poly to the studs; right against the tar coated Kraft paper. I have frequently seen thick black mold between them. We never put a vapor barrier on ceilings, but cathedral ceilings, more often than not, get Kraft faced and don't cause any problem. So, moisture condensing on your insulation or in your walls is bad, but it's going to happen at times. Not letting the moisture get out is real bad, and will only get worse because the R-value decreases as insulation gets wetter. Just keep sealing and caulking to stop the airflow and you'll be greatly reducing the amount of moisture that gets in the wall in the first place.

I just re-read your post after typing that reply out. You said to just keep caulking and stop a much air as I can. Were you were telling me to just leave it as it is?