Non-typical insulation of barn / garage
I live in Interior Alaska Zone 7/8. I have a rather large barn pole barn that needs to be insulated so it can be heated. Since it is rural there is no code but i want to ensure that i do not do something that damages or ruins the building over the long term with that said money is not unlimited. The space is intended to be heated to just above freezing 35 to 40 typical with the ability to warm even more during use. Not a business just personal use during the week.
Barn size is 50×60 with 14 foot walls.
Exterior sheathing is metal with 2×6 girts used to attache the metal to the poles in the barn.
Poles are very large
Interior is 2×4 stick framed leaving a 15 inch gap between the back of the stud to the back of the girt… add another 1.5 inches to get to the metal. Total gap is 16.5 to 17 inches
How can i economically insulate these walls for this type of non living area to meet my needs without in the long run compromising the building to mold rot etc.
My initial plan was 1 inch Rtec Foam places against the girts (1.5 inches ) from the metal sealed up with tape and spray foam. Then R13 batt insulation in the walls. Wait to see how that works for heating efficiency with the possibility of filling the large space with blown in cellulose (would be difficult to dense pack that large volume area.
I was only thinking of using the foam to keep the insulation from touching the metal.
Worried about condensation. Also spray foam is really not much of an option . very rural here so cost is double to triple normal applications in the city.
Want to do this right but can not spend all my budget on just this phase of insulation.
Thanks
Greg
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here are some pics for visual reference
one more picture of outside... distance is deep on previous picture as stated in the post.
James,
Since you live in interior Alaska, any investment in careful air sealing and insulation will pay you dividends. Your climate is extreme, so it's worth investing more in this work than it would be for a homeowner in Massachusetts.
The most difficult aspect of insulating this type of building (a pole barn with steel cladding) is to make sure that you have a very good air barrier on both sides of your walls.
One of your photos shows that you have already started framing up your 2x4 walls and installing fiberglass batts. That's too bad, because the photos don't show an exterior air barrier.
Your suggestion to install an exterior layer of rigid foam with taped seams is a good one. (However, I don't see any taped foam in the photos.) If the foam you plan to install is R-Tech (not Rtec), that is a brand of EPS foam with some type of facer. It will work as an air barrier, as long as it is very carefully taped with high-quality tape.
If you intend to use thin R-Tech as your exterior air barrier, you should contact the manufacturer to get information on its vapor permeance. Thin exterior foam needs to be vapor-permeable, especially in your climate, and I'm not sure whether the facers on R-Tech are vapor-permeable. If you install a type of rigid foam that isn't very permeable in this location, you need much thicker foam in your climate. For more information on this issue, see Calculating the Minimum Thickness of Rigid Foam Sheathing.
If you decide that you don't want to install rigid foam in this location, there are other air barrier options: plywood with taped seams, OSB with taped seams, or housewrap with taped seams. Housewrap won't perform as well as plywood or OSB, however, because it is harder to make housewrap airtight.
You might want to consider increasing your framing size from 2x4 framing to 2x6 framing -- in interior Alaska, 2x4 framing with R-13 batts is pretty wimpy. If this were my garage, I would install much more insulation than you are contemplating.
However you decide to detail your walls, remember that paying attention to airtightness is the most important aspect of your work.
Thanks Martin. What you see in the picture is the way i got the property from the previous owner. I have put in an all stop to plan this out some.
Ok now i am a little confused. I thought i was trying to conduct stop vapor from going out and then would install with no interior vapor barrier to allow it to dry to the inside.
What i am reading here is allow the vapor to pass through to the outside. Would this not create condensation on the metal and the wooden girts leading to problems?
Also the articles are good in concept for me but they do not cover metal exteriors so that is a little different and they do not cover the size of the gap i have only 2x4 and 2x6. Although it is not really a stud cavity my area is 2x19 ha.... Remember i am open to blowing this cavity full of insulation if needed but i would rather just batt it since it is not a home or living area and just a occasional use shop. BUT do not want condensation damage either.
Understanding the physics here is a little difficult for me.
Thanks all
James,
The principles are explained in the article I linked to: Calculating the Minimum Thickness of Rigid Foam Sheathing.
It's perfectly OK to choose a type of rigid foam that is vapor-impermeable, and to install it on the exterior side of your stud wall if you want. But if you do that, you have to make sure that the R-value of the rigid foam is high enough to keep the interior surface of the rigid foam above the dew point in winter.
In your climate zone, that means that the rigid foam must have a minimum R-value of R-10 for 2x4 walls (and actually, probably more than that for interior Alaska -- I'd go with at least R-15), or R-15 for 2x6 walls (let's call it R-20 for interior Alaska).
Exterior foam works fine -- but it has to be thick enough.
James, I don't understand why the stud wall was built so far from the girts, but with that large of a gap between your inner stud wall and the girts, the foam would be a waste unless you insulate between it. I think the best choice might be to install the foam against the girts, making sure to air seal as you go with tape, caulk, acoustic sealant, etc. your foam would become the exterior air barrier. Then I would use housewrap as the air barrier on the outside of your stud wall. Then I would blow cellulose or fiberglass between the foam and house wrap. Your stud wall could remain uninsulated and be your mechanical and wiring chase. The air barriers on both sides would have no holes.
Since that assembly would have excellent drying potential both ways and has no sheathing to condense on, I don't think you need a minimum thickness of foam against the girts. However I would double check with Martin or Dana on that.
Also, Dana would suggest foam without a foil facer...preferably eps, which has stable long term r and better permeability than xps.
Rick,
If the rigid foam layer isn't thick enough, condensation can form on the interior side of the rigid foam. In some cases, enough condensation can form to run down the foam and puddle on the bottom plate. You don't want to depend on inward drying to handle that much condensation.
Instead, what you want to do is to specify rigid foam that is thick enough to avoid the condensation problem.
Thanks all for the comments... although it was not good news economically at least i now know what it needed. Does this also apply to the shed style roof in the back of the barn. I think the pictures show what i am talking about. Similar to cathedral ceiling... totally unvented and really no way to vent.
Also can someone explain why a 2x4 wall only requires R10 and 2x6 requires R15. I am really trying to understand the science behind all of this and even read the long technical post on dew points.
Finally, since this is a metal clad pole barn similar to commercial buildings... why is it that big commercial buildings get away with like R19 roll batt style insulation with a white vapor / protective barrier.
Thanks again guys...sorry to be dense just not an engineer by trade and trying to understand the reasons not just looking for an answer.
James,
You don't have to install rigid foam insulation on the exterior side of your wall if you don't want to. In your case, you could use carefully installed housewrap as your exterior air barrier, or plywood.
But if you want to use rigid foam, your wall will no longer be able dry to the exterior. So it has to be thick enough to avoid condensation. This is explained in my article, Calculating the Minimum Thickness of Rigid Foam Sheathing.
The article also explains why 2x6 walls need thicker foam. (Basically, the thicker fiberglass in a 2x6 wall keeps the surface of the foam colder than the thin fiberglass in a 2x4 wall. So the rigid foam has to be thicker, in order to be sure that the interior of the foam is warm enough to avoid condensation.)
If you want to know how to build an unvented cathedral ceiling, there is an article that explains everything you need to know. Here is the link: How to Build an Insulated Cathedral Ceiling.
Martin: Thanks for all your help. I now understand the foam course of action now much much better. Still trying to understand the whole science. I am excited (economically) to hear that foam is not necessary but after reading the technical blog concerning dew points it would seem that the Tyvex option with either blown or batt insulation would still create condensation on the Tyvex. I am not overly concerned about it since this is a profession forum just once again trying to fully understand the science.
1. With this option i assume that the Tyvex in position "C" would be installed as it would on any exterior building IOT ensure it operates correctly.
2. Is a vapor barrier needed in position "A" or "B" or would Tyvex be a better choice, if so would it be installed in the same manner or would it need to be turned the other way.
3. I would like to phase the cost of this and would like to install batt insulation first prior to the blown. I am assuming that the "DEAD" airspace would not really work since it is not really dead. Just wanted to make sure that batt only would cause problems.
I will ensure that the Tyvex is properly sealed with either blown insulation, chalk or acoustical chalk
I have attached a cross section drawing of the barn to paint a visualization to make sure i understand.
Again thank you for all your help.
James,
Ideally, you need a really good air barrier at the exterior. That's going to be hard at location C on your drawing. How will you keep your air barrier intact at the intersection between the girts and the posts? Do you intend to wrap the housewrap around each post? I suppose you could -- but it will be hard to keep this layer airtight if that is your plan.
Although the Tyvek will be cold in winter, there will be no condensation on the Tyvek, because Tyvek is vapor-permeable.
In your climate, a vapor barrier (polyethylene) at location A is a good idea.
The use of batt insulation rather than cellulose is worse for many reasons. If you decide to use batts, you have to come up with an insulation plan that has no "dead air spaces" between your interior polyethylene and your exterior Tyvek.
Martin: It has been a while and finally it is spring here in Alaska and work can begin again. Your help above has been great. I am preparing to begin the insulation process on my barn. I attached a power point to make visualization easier.
My plan is to go with what you suggested in earlier post and install house wrap as foam was just to expensive (recent quote of 7300 for 3-4 inches.
My plan is to use house wrap at position C and seal it very well. Seam tape for all joints and thinking about spray foam at the bottom and at the junction at the post. then I will blow cellulose to fill the void and ultimately placing poly at position A.
As I prepare to do this I just wanted to check back to make sure that I understood correctly that I am good with this procedure. I Do Not want to jeopardize my girts and have ultimate rot, or have wet insulation leading to mold and reduced R value.
Also I wanted to ask if 15 or 30 pound felt might be better. As I understand it felt would allow any condensation that might collect to wick to the outside easier as Tyvex only allows vapor out. Just a thought I am not partial to either. If felt is an option is there a preferred way to seal the seams.
Just for some information on Alaska construction cost in this case.
OSB = 15 a sheet equalling 840 for the project
House Wrap = 175 a roll (9x150) for approx 350 for the project
30# felt = 25 roll (216 soft) = 225 for the project
All these cost are less staples and tape
Like i said just wanted to check back before i pulled the trigger on construction.
thanks for the assistance with this project
Greg
James,
Ideally, you need an exterior air barrier. You are going to try to get a tight air barrier with Tyvek. That's going to be tough, but it's not impossible. (You can forget your idea of using asphalt felt instead of Tyvek. It's impossible to seal the seams of asphalt felt in an airtight manner, so you can't use asphalt felt as an air barrier. When it comes to allowing your wall to dry to the exterior, Tyvek is better than asphalt felt. You wrote that "Tyvek only allows the vapor out," but that's how walls dry to the exterior -- by evaporation, which means by allowing the water vapor out.)
There are two problems with your approach:
1. How will you tuck Tyvek into the corners where the girts meet the pole? Do you plan to smush the Tyvek in there, and then wrap the Tyvek around the pole? That's the only conceivable way of maintaining an air barrier. It's possible, but tricky.
2. There will be some air leaks, inevitably, due to the fact that the Tyvek will be hard to seal at the bottom (I assume there is a concrete slab floor -- you need to buy Siga Wigluv tape if you expect to seal the Tyvek to concrete), hard to seal at seams (because there is no plywood to press against), and due to the inevitable holes near fasteners.
It's a barn, so perfection isn't really necessary. However, the success of your plan depends on how fussy you are creating this exterior air barrier.
Creating an exterior air barrier would be a lot easier if you installed plywood or OSB on the interior side of the girts. Then you could tape the plywood seams, and seal the seams between the plywood and the posts with high-quality European tape like Siga Wigluv.
Martin: thanks again for the reply. As for the sealing of the Tyvex I happen to have a girt that is just the correct height for a seam and would use that for the seam to seal against and give me a firm surface to place tape. As for the floor and post my plan was to seal this with spray foam. I would shoot a small afar along the bottom and between the post and wall girts to seal these areas off and tie that into the house wrap. I was thinking that might work to seal the area.
thanks for the reply on the felt, i had a sneaky suspicion on this but I am really concerned about condensation and water and wanted to make sure i was able to move out and not collect. Like i said i do not want rotted girts or wet and moldy insulation. Once this is done having a rot issue or mold issue will be difficult to repair.
Finally, I re read some of your post and saw where you said that Tyvex would not condensate in the winter due to vapor permeability. I assume OSB which is what i would use would do the same because wet OSB is ultimately a no go. I now understand the air barrier piece and also the foam thickness piece if I were to have gone that route and dew point just trying to make sure that I have the final details to make this happen. If you think the OSB is the better route then definitely would go that way... either way it is WAY cheaper than spray foam and spending the extra money now would be better than problems down the road that are impossible to resolve.
Again thanks for the post and help. I am sure I will be back for more help on different items... this southern boy is still trying to learn construction in Alaska.
Hopefully someone can chime in and hopefully Martin will see this as he was very helpful on this long thread attempting to solve my pole barn issues.
Bottom line as you read this thread I was ready to begin construction and then was sent out of town on business for 4 and half months... needless to say i did not get anything done, missed the beautiful Alaska summer and just got back to reports of snow. I have decided that i can not wait another year and I am going to continue.... with all of that said while away i had a brainstorm on how to complete this construction a little easier and maybe more economical in the long run but want to run it by the professionals to ensure i am not off track...
If you read the thread I am not deviating dramatically from the original plan but tried to improve on it to make it easier to seal the area.
Please chime in on the plan and refer to the attachment to cross section as a visual of the proposed project.
The NEW plan is to construct a a NEW stud wall minimally 5.5 inches from the existing wall that i am stuck with from the previous owner. I can increase the gap based on the amount of insulation wanted or needed. 5.5 inches would give me 9 inches of space to blow in cellulose for insulations ...rather than the 15-18 inches in the original plan.. referring to the cross section now i will fill between A and B. Originally B and C was the insulation fill plan. Although this adds wall construction cost it is actually a saving in the long run over filling the large cavity with insulation but comes at a cost of reduced R value. I believe the original plan was greater than R60. I would use TYVEX at position B on the interior side of the existing stud wall. I could stay with OSB but would rather go with TYVEX since it is a good deal cheaper and in this position should be much easier to install correctly and air seal. Position A would be 6 mil plastic with the cavity cellulose insulation. This cavity should provide R30 in the walls and I am kicking around making the gap the width of a 2x8 giving me around R38
Doing it this way makes it much easier to install the TYVEX product due to the fact that i would not have to work behind the existing stud wall and it would cut out the post as an obstacle to work around. As with the original plan i would still work to achieve the best air seal possible but after looking at it and re reading Martins post this seems to be more feasible.
Question: Do you think this is a better option than originally planned? If i am way off I will just go back to plan A and cover the girts with OSB, tape and seal, put plastic over the existing stud wall and blow large amounts of insulation in the cavity. Also with the cold weather already here this plan negates the need for spray foam that might be an issue with the cold weather and I could use tape to seal the TYVEX. The original plan calls for spray foaming the areas around the poles and the bottom of the OSB where there is irregularity in the concrete and gaps.
The unknown on my part is .. WILL the large gap behind the insulation be an issue... I had not plans to put effort into air sealing the gap behind the insulation and to put all air sealing efforts to the existing stud wall hence will be drafty behind the TYVEX.
Hopefully this all makes sense and provides a vivid picture that enables a response.
Thanks again
James,
It sounds like you intend to use Tyvek to confine your blown cellulose. That may not work. If you want to install cellulose with the dense-pack method -- and that's the best way to do it -- any flexible membrane needs to be very well attached (with close staples) to resist the pressure of the dense packing. It's possible that Tyvek would work, but I haven't heard of anyone who has tried it.
You need a really good air barrier in this location to make the assembly work. I would advise you to use OSB with taped seams, not Tyvek.
Your idea (to build a new building inside your old building) will work, as long as (a) you maintain continuity of the air barrier at the wall/ceiling juncture, and (b) you come up with a way to address the huge thermal bridge at your slab edge. The best way to address heat loss through the slab would be to add insulation above the slab where it is exposed to cold air (between your multiple exterior walls) as well as to add vertical insulation at the slab perimeter.
Why add another layer of 2x4, if you have such a fantabulous cavity already ? Suggested buildup:
diffusion open fiberboard 35 mm attached to inside of the girts
diffusion open air barrier, wrapped around the inside of the poles
cellulose in the cavity
OSB on the room side of the 2x4 studs to tame the cellulose, and act as a vapor barrier. Tape seams, add sheetrock to taste.
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