Insulating a pole barn *loft*
Hi,
I’ve read many posts about insulating pole barns, but nothing seems to address my particular scenario. I’m building a 24x36x16 gambrel-style pole barn near Seattle, WA. It will be two stories — the ground floor (concrete with visqueen underneath and the back 12’x12′ will have foam underneath the concrete) will be a shop, and the upstairs is planned to be an ADU. There will be a door separating the ADU from the shop, at the top of the stairs.
My question is whether or not this will present a more insulatable space than the normal barn being referred to in other threads here. I plan to frame in the ADU completely with 2×6 studs, with 2″ cut out so that it will be flush with the posts. The roof will have a continuous vent, and I’ve signed up to have the building wrapped in tyvek as well. The floor system for the loft will be glu-lam beams making the 24′ span, and TJIs running perpendicular spanning the 12′ between glu-lams.
Is there a way to efficiently insulate this space despite it being a pole barn that’s not spray foam?
GBA Detail Library
A collection of one thousand construction details organized by climate and house part
Replies
Reimhagen,
I assume you read my recent article, "Insulating a Pole Barn."
As the article makes clear, the key to designing any insulated building -- including a pole barn -- is to make sure you have a continuous air barrier. The missing element in many pole barns is sheathing -- wall sheathing and roof sheathing. These days, builders depend on OSB or plywood sheathing to act as an air barrier -- so if your building lacks sheathing, it can be hard to insulate.
You haven't fully described your planned wall and roof assemblies. If both your wall assembly and roof assembly have OSB or plywood sheathing, you're in good shape -- as long as you think through the necessary steps to make your air barrier continuous, without any gaps or hard-to-address penetrations.
By the way, I'm not sure how your 2x6 studs intersect your posts. A sketch would help.
Hi Martin,
Yes, I read your article. I signed up for GBA Prime just so I could read it! Looking forward to more great content in the future.
The building isn't built yet, but the company building it is hesitant to deviate from their standard way of doing things without giving me an exorbitant upcharge. I was happy enough that I could get them to install tyvek around the structure for me. I'm not exactly sure how they're going to do it, but I imagine I'd just be looking at the backside of the tyvek in between the girts. I can ask for further details if needed.
I've attached a rudimentary diagram of a wall assembly I was thinking about. Nailing OSB to the girts, sealing the seams with canned foam or caulk sealant, and then framing in a 2x6 wall assembly and then insulating with rockwool. Let me know if it's unclear or if I'm just overlooking something.
Reimhagen,
If you build inset wall panels between the posts, your wall won't have any continuous air barrier except the Tyvek. (The vertical seams between the posts and your proposed OSB panels will be impossible to seal -- there will be seasonal movement in the posts that cause the cracks to open up.)
Can Tyvek be an air barrier? Maybe. It's really, really hard to get it right -- because builders always rip Tyvek (with hammers, fasteners, and ladders) during siding installation, and because the perimeter of each piece of Tyvek needs to be joined with the rest of the air barrier (at the floor assembly and roof assembly) with some type of durable method of air sealing.
I suppose the problem must be similar to installing finless windows. If the caulk sealant does a kind-of OK job in that case, would it also do a kind-of OK job here? Granted for windows they're more concerned about water than air, but seasonal movement must be a concern too. A caulk sealant like DAP dynaflex sounds like it has greater tolerance than canned foam as well to movement.
If you think the caulk sealant will not be sufficient, then what about caulked/canfoamed + taped foam boards instead of the OSB? Would that withstand movement more?
Just had an idea -- what if instead of nailing the OSB to the girts, if I nail the OSB to the studs along the backside of my 2x6 wall assembly? The assemblies would be raised into place between the posts and the perimeter would be sealed using sill plate gasket tape and caulked, if necessary.
I believe this would make the OSB move less as the assembly would be very rigid, and the foam gasket is more forgiving to movement. It may even contribute to reducing movement as the overall structure would be more rigid...
Diagram attached.
(more thoughts)
Perhaps using structural screws (e.g. GRK fasteners) instead of nails when attaching the wall assembly to the posts will help a bit in preventing movement between the posts and the wall assembly to keep that seal airtight.
While I get the impression that it's typically seen as an outdated approach, perhaps the "Airtight Drywall Approach" would be appropriate for establishing a continuous air barrier in this particular case.
Here's a GBA article on the subject: https://www.greenbuildingadvisor.com/article/how-to-hang-airtight-drywall
And a BSC article: https://www.buildingscience.com/documents/information-sheets/air-barriers-airtight-drywall-approach
Worth a little research at least.