Best way to insulate an existing pole barn that has metal siding and no wrb?
I have read many versions of this question (as well as many answers) on your site, and at this point I am looking for the most current responses and solutions to this age old problem. I am well aware of the inherent pitfalls associated with pole buildings but it is what i have and i am hoping to make the best of it.
I reside in Central Oregon (Zone 5) and I am planning on making a workshop within a 30’x50′ pole barn. The shop will be approximately 20’x30′ and i plan on heating it during the winter. It has metal siding mounted on 2×6 horizontal girts. The girts are mounted on the exterior of 6″x6″ poles which are spaced 10′ apart. There is no sheeting or weather barrier under the siding. I realize removing the siding and starting over would be ideal, but that is no an option. I do plan on framing interior walls to hang either OSB or drywall on the interior.
What are my best options to insulate my walls?
Thanks,
Darryle
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My 2 cents on pole barn insulation: I have insulated a pole barn by applying polyiso sheets on the inside of the 2x4 girts and trusses, butting up to the 6x6 posts. After taping all of the joints I applied osb to all of the walls to give a durable surface that I could hang tools on, add shelves etc. It would be very difficult to install the insulation in thicknesses that meet code, however the taped installation provides a tight envelope. The exposed polyiso on the ceiling also may be a code problem. And the concrete slab at the perimeter will be a definite heat loss.
I suppose you could strap the ceiling and install cellulose over the polyiso if you want to get closer to code. There would need to be good ventilation detailing to avoid ice dams. If you haven't built it yet, use energy heel trusses.
A friend of mine is looking to build a similar building. He decided on a traditional foundation with framed walls and a pole barn roof structure on top.
Thanks Joel, I appreciate you taking the time to answer. Unfortunately my barn was built about 20 years ago. That much polyiso: seems expensive? Almost comparable to spraying foam?
That's what is confusing about all this. Previous post outlined similar tactics as yours, but they were shot down and/or modified.
Darryle, there are various ways you could address your situation, so there are many possible answers. The simplest would probably be to spray polyurethane foam against the back of the siding. The new HFO-blown, closed-cell foam is much more environmentally friendly than conventional foam, and is higher R per inch. It should be able to be installed for about the same price as conventional, though it's still new enough that some companies may charge a premium for it.
Alternatively, and more environmentally friendly, would be to just build a more or less conventional wall assembly but do it from the outside in--start with a good WRB sealed to the girts and posts, then add sheathing (ZIP system osb installed inside-out would allow you to air seal effectively from the inside), then frame the wall and insulate the cavities.
Michael, thanks for giving me your inout. I realize spray foam would be the best option, but costs always enter into the equation. However, If I did use spray, do I use batts in my wall on top of the foam? No need for WRB or any sheeting with spray foam right?
Do you see any advantage of framing a 2x4 wall on top of (or to the inside of the building) the poles? Creates bigger wall cavity, more insulation?
Is it ever good of beneficial to put rigid foam on the inside? Starting from the outside moving in, would it be problematic to place WRB, osb sheeting, fiberglass batts, then rigid foam over everything, including the poles before finishing the inside with osb or drywall?
Thanks again
Darryle, I wouldn't trust spray foam to be a perfect WRB, or to remain one long-term, without knowing a lot more about your project. A flash-and-batt design could work, as long as your R-value proportions are correct to avoid moisture accumulation.
Providing room for additional insulation is usually a good idea. Just watch that ratio if it's a flash-and-batt assembly.
Rigid foam on the inside can work fine, if you're not in a cooling-dominated climate, and the wall can dry easily to the exterior.
It's hard to give solid advice because every pole barn is different, especially at places like the floor-to-wall and wall-to-roof intersections. Do you have a good architect, engineer or builder friend nearby who could look at what you have and provide advice?
Thank you again Michael! I know without standing in the building and looking at what I am seeing, it can be difficult to advise.
When you refer to the flash/batt as we discussed, are you referring to the issue with condensation accumulating because there is not enough spray foam. It is my (very basic) understanding that if you use spray of rigid foam against the metal siding it has to be thick enough to prevent that dew point from happening on the inside of your foam. In other words, I have to have enough spray foam or rigid foam to keep the warm air away from the outside air???
At this point the wall will sit on an existing concrete slab and I planned on adding the framing so i could hang drywall or osb on the ceiling, leaving a cold attic space above blown in cellulose.
Unfortunately I don't have any help around here. I actually checked with a pole barn builder and they said the way they are insulating their buildings is just to place batts against the metal siding and closing it up. When I asked about the condensation issue and moisture ruining the fiberglass batts, he said there would be moisture, and that is how it is designed to behave. He said it would dry to the outside. He claimed the insulating companies are the ones doing it that way for them??? Maybe I'm wrong, but what little i know is fiberglass doesn't like moisture. In fact I always thought there were only a couple of types of insulation (aside from foam) that even tolerated moisture.
So that's what I am dealing with. I certainly appreciate the advice and knowledge you are sharing. I know pole buildings are very difficult to seal/insulate, and I know I will never get my pre-existing barn anywhere close to 100%. I just hope to put my best foot forward while trying to come up with a reasonable solution that fits within the parameters of my building.
Darryle
Darryle, yes, you need to be concerned with moisture condensing on the interior surface of the foam. You can read more about it in Martin's article here: https://www.greenbuildingadvisor.com/blogs/dept/musings/calculating-minimum-thickness-rigid-foam-sheathing, and in a Fine Homebuilding article I wrote: https://www.greenbuildingadvisor.com/fine-homebuilding/why-flash-and-batt-makes-sense.
While I often learn things from tradespeople--in fact, I make a point of trying to learn something new from everyone I work with--I do not put blind faith in their understanding of building science. I've put significant effort into learning about the fine points of building science for over ten years and still learn new things regularly. That said, if your siding is either corrugated or rib-panel (aka agricultural style), it does have built-in ventilation channels; if those are open at the bottom, and especially if they're also open at the top, they can provide a lot of drying potential. If they're closed with flashing or trim strips they may still offer some drying; it's hard to know without seeing it in person or at least a photo or drawing.
Most insulation materials do ok with a little moisture accumulation now and then. If fiberglass or cellulose get saturated, though, they can compress and lose R-value. Mineral wool is more rigid and dries readily after being loaded with moisture. Foam, either open-cell or closed-cell (same resin, different blowing agents and different finished qualities) is not affected by water, but open-cell foam can hold, and pass moisture, while closed-cell foam blocks water in all forms, as long as it doesn't crack. (The pole barns I'm familiar with are not the most rigid of structures.)
Foam in all forms has a higher carbon footprint than other insulation materials, especially standard closed-cell sprayed foam and XPS rigid foam (the blue, pink or green type), so like most green builders and designers I try to minimize my use of foam, but sometimes it's the only thing that will do the job both effectively and affordably.
Assuming your structure is already rigid (it probably is if still in good shape after 20 years), you need to worry about four things, in this order:
1. Block water. Your siding blocks most of it, but not all--so you need a surface below your siding that will stop stormwater from entering your wall assembly.
2. Block air flow through the wall. The exterior sheathing is usually the easiest location for this, but the air barrier can be anywhere in the assembly, and you can have more than one air barrier. (Just no more than one vapor barrier.)
3. Slow thermal transfer. Once you have liquid water and airflow blocked, you can add insulation.
4. Control water vapor movement. There are many options, but the key is to keep water vapor from condensing inside the wall cavity. Either let it pass cleanly through, keep the interior of the condensing surface warm enough (in your case, with a flash coat of foam) to keep if from condensing, or stop it from entering the wall. In a heating-dominated climate it usually enters from the interior. You can't keep it out entirely, so it's a good idea to use a variable-permeance membrane that allows the assembly to dry to the interior if necessary.
There are many ways to solve your problem so it would probably be most effective if you drew out what you think would work best and post that here for comment.
First and foremost, Thank you again Michael! I know I am not doing a good job of helping you help me; no drawings, no photos.
Starting from the outside and working in...
My existing steel siding, 2x6 girts that the siding is nailed too, WRB, OSB (both fitted between the 6x6 posts), batt insulation, all closed in with drywall or OSB.
1) Does the OSB act as my air barrier and vapor barrier?
Thanks again,