air and vapor barriers for pole barn batts insulation. Also pole barn framing. Pros?

[bob112]

I am designing a pole barn for myself. I am in the engineering field so doing things by the numbers but this is not my specific area of work.

I have a couple questionable areas and hoping some can help. My insulation is my primary issue right now. Not so much the insulation, as the membranes on each side. Please don't try to sell me on spray foam. I know the pros of it but there are specific cons that make it not work for me. To obtain optimal R values with glass, you need to obtain air seal on BOTH sides on a wall space. What I see around here is guys buy glass with a vapor/air barrier on the interior side and push that against the barn sheeting. This presents a real and quantifiable issue with wind washing and convection losses in the batts. In an effort to combat this, I have spec'd a Tyvek House wrap layer on the outside of the framing to be between the batts and metal siding. This will serve to seal the air on the outside yet provide a reasonable perm rating for vapor migration through the wall.

About all I can find for batts locally has this vapor/air barrier that faces the interior. Now, this technically gets me the air seal that I need BUT I need to examine vapor migration through the wall. Simple physics dictates that high moisture will move to low moisture, high pressure to low, and high temp to low. I need to somehow determine how moisture will move through the wall. My midwest climate has it ALL..... From nasty colds to hot and muggy. This means moisture will move in both directions. Now the Tyvek should help limit wet coming in but vapor will work through the layer. It would work into the batts and hit the interior layer where it could not leave, but that still has to be better than the locals way of using nothing on the outside so humid air is free to invade the batts at will. In the Winter, any moisture that works through my int walls could easily migrate and vent to the outside of the building. I need to determine a balance here and predict the outcome to ensure I have the right layers in the wall construction.

I have learned through research data by Building Science Corp that most people are getting it wrong, not understanding how to air seal, or that vapor will move in both directions. I wish I could have a chat with them but they are a big deal.





#2. I am still working on the framing structure of the building. We have design a custom glulam truss to span 12ft oc, and intend to use hangers in the walls and roof. 2x8s on edge 2ft oc in the roof, and 2x6 on edge in the walls. The hangers present a couple questions and challenges and curious who here that hung them and can help with procedure planning? I intend to build custom jigs to install them on the poles and trusses but that is still a LOT of them. I plan to shoot specific ring shank nails. However, one issue is coming up realizing these will see some amount of tension forces that the hangers are not really rated for? At least I cannot find it. It should be minimal but does concern me.

Any of you guys that might have a flush wall/roof system in hangers like this, what do you think? Is there a faster hanging system?

 

[timswi]

I certainly don't have any answers beyond the research that you stated...my question is: what are you doing with this building?....I and almost everyone I know have pole buildings and haven't had any moisture/rot problems...Personally, I used Tyvek under my vinyl siding....Surprising thing is, it falls apart over time..The weave gives way...had to remove some siding once and was rather surprised but not shocked by this.

Anyway, there is more thought and observations in the post above than I personally have generated in a lifetime of DIY---Kudos to you!!:drink:

 

[tjkubota93]

Most houses built in my area have siding, then a moisture barrier (tyvek), studs with fiberglass, then clear plastic sheet, then sheetrock.

I have been told the reason you don't caulk between your siding boards and seal up 100% or the reason brick veneer has weep holes is to let moisture out. (Because it will get in, from rain or condensation)

 

[bob112]

Tim, I am curious?! Was this actually Tyvek brand? Tyvek I thought was a spun fiber type product, not really woven. I know there are a LOT of knock offs and I really wanted to go that route due to costs but seems you can't get the air seal and perm rating with the junks stuff. I would be severely pissed to learn my expensive Tyvek craps out in short order, leaving me with a leaky building.


To clarify a couple things, I will certainly be generating a large amount of moisture in the air inside the building but I intend to build ways to manage that. My primary reason the the air seal is efficiency! If you go buy batts that are rated to R-19, that *assumes* a perfect air seal on both sides. Open one side up and you will probably have about an R-5. The entire building is designed as an efficient structure, all the way down to the insulated and radiant heated floor.

 

[bob112]

"Most houses built in my area have siding, then a moisture barrier (tyvek), studs with fiberglass, then clear plastic sheet, then sheetrock.

I have been told the reason you don't caulk between your siding boards and seal up 100% or the reason brick veneer has weep holes is to let moisture out. (Because it will get in, from rain or condensation) "




Appreciate that! That seems to be right inline with my thinking and reasoning here. Gotta know water WILL move through someone. With my Tyvek layer, there is free air movement between the metal and Tyvek for any air drying. I think where things have went wrong for others is using a plastic (no vapor perm rating) on the outside which effectively locks moisture.

I only wish I had other options than Tyvek. Stuff is wimpy thin, and stupid in price for what it is.

 

[timswi]

Tim, I am curious?! Was this actually Tyvek brand? Tyvek I thought was a spun fiber type product, not really woven. I know there are a LOT of knock offs and I really wanted to go that route due to costs but seems you can't get the air seal and perm rating with the junks stuff. I would be severely pissed to learn my expensive Tyvek craps out in short order, leaving me with a leaky building.


To clarify a couple things, I will certainly be generating a large amount of moisture in the air inside the building but I intend to build ways to manage that. My primary reason the the air seal is efficiency! If you go buy batts that are rated to R-19, that *assumes* a perfect air seal on both sides. Open one side up and you will probably have about an R-5. The entire building is designed as an efficient structure, all the way down to the insulated and radiant heated floor.

Been 10 years that's why I'm not really complaining but I'm pretty sure that it was Tyvek although it might have been Lowes brand not really sure...looking at them in the store at the time they looked like exactly the same thing appeared to be a weave --Burlap if you will...

Perhaps things have changed/improved over that time...Back then only the OCD's used wrap on a pole building so there were no real test cases for me to ask about. I plead guilty to the OCD thing.:grumpy:

Either way, no rot with or without the Tyvek..a J channel caused me a small problem, nothing else.

 

[tbrooks26]

Tyvek is an air barrier, not moisture barrier, as above stated. I have seen the cheaper woven products breakdown as well, but not actual tyvek. I hear that tyvek will be going away soon as it is believed to trap moisture in cases. I find this total BS personally. If there is that much moisture in the wall, there are problems elsewhere with construction, flashing, sealing, etc.

You are correct you do not want a true vapor barrier on the interior of your walls. They do have breathable smart barriers now for this purpose, I can't think of a name off the top of my head, but they are not too expensive. The real problem with all buildings is that you want to air seal and stop infiltration, but it is all but impossible because any amount of moisture finds its way in much easier than it finds it way out. If you are generating lots of moisture inside, I hope you are building with pt lumber, just in case. It sounds like you plan on an air gap between the metal and tyvek? -thats a great place for condensation and moisture.

On my home, I will be using felt paper on the interior of my exterior walls. Mainly because I am using reclaimed lumber with lots of holes and cracks for wall covering, and I need something black behind it. I will be running it vertically, on 16" oc studs, so it will be lapped every 32". It will help to seal air better by installing vertically, but as most people do not know felt paper is also permeable and will not serve as a true vapor barrier.

As to your framing, I can't exactly picture what you mean. I will say it is amazing how some things that are way under-engineered can last a very long time, so you may not need be as concerned.

 

[Tractor Seabee]

Bob,

Take a look at this stuff. I have seen it used on many PEMBs herb in the NW. There are several brands available. The manufacturer's give you free advice and engineering help on Psychometrics which is your expressed problem. Stuff up here like fiberglass batts; if not vapor sealed very well on the inside face it is not long condensed moisture puddles on the vapor barrier, overloads the tensile strength somewhere and the dominos start to fall.
Ron

Object moved

 

[timswi]

I know the OP didn't want to discuss foam, but open cell spray would do a nice job...Stay away from closed cell, cheaper but disaster causing where there is potential moisture involved. Don't listen to the sellers.

The amount of effort and research involved in this might be a cause for checking on this approach...Just sayin'

 

[Jim Timber]

If you're going to run a high moisture producing heating source or have a wash bay, you want a vapor barrier or you will have condensation issues.

I put a membrane under my steel roofing because it can condense and drip when the humidity is right in the spring and fall here. You get rain. Then if you have insulation under that, you get water pooling inside it; which results in disgusting black pools sagging down from your vapor barrier. I've been in more than enough pole barns where they just stuffed the ceiling and put plastic up and it was a bad decision. The paper backed fiberglass doesn't provide a good barrier unless it's sandwiched between sheet rock and the studs, and even then I think it pales compared to a proper 4mm (or thicker) plastic with taped seams.

Tyvek allows water vapor to pass from inside to outside, but not the other way. It's hardly "going away", but they have found that when it's installed under un-insulated vinyl siding (insulated is the way to go with vinyl btw) the sharp edges of the vinyl abrade it when they move from temp swings, thus negating it's effectiveness. So, yes, they're moving away from Tyvek in those applications, and in traditional facade's like brick which have always used 30# felt instead - but it's not because the Tyvek doesn't work when used correctly in other applications.