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Insulating a pole barn question(s)

I have a 24’x34’ pole barn that I want to insulate so I can add some intermittent heat while working out there. I live in Iowa. In the winter, we park our cars in the front and my wood shop is in the back. There is a ridge vent along the entire ridge (34’). No soffit vents or gable vents. I do not want to add a ceiling. This isn’t our forever home and only need it insulated enough to trap some heat in while working out there - maybe 3-4 times per month, for a couple hours at a time, during the winter months. I can’t justify the cost of spray foam (So please no advice on spray foam). The pole barn is a wood frame, poles are 6’ on center, and steel on roof and walls. No house wrap between wood and steel.

I was going to start with the roof, since that’s where most of the heat will escape, and plan to insulate the walls later. Here’s my plan....

I was going to start by putting R-13 unfaced rolls of fiberglass insulation between the purlins, right up against the steel. I got a really good deal on some 1.5” ISO foil faced foam sheets (R10). Planned on nailing those to the purlins over top of the insulation. (So from outside in - steel, R13 between purlins, foam sheets). The foil face should act as a vapor barrier. Was going to tape the seams between the sheets and the seam between the foam and top chord of the trusses.

Any potential problems with this plan? Should I be doing it differently? Do I need an air gap between insulation and steel? Trying to avoid condensation - however is condensation even an issue since I won’t be heating it very often? Thanks!

Asked by Doug Kremer
Posted Nov 15, 2017 2:11 AM ET


8 Answers

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This question is posted frequently on GBA. The bottom line seems to be that pole barns are hard to insulate, but it is possible to improve how your structure performs (especially if you are trying to convert the barn to living space).

Search for "insulating a pole barn" to find related threads. Here is one to get you started: http://www.greenbuildingadvisor.com/community/forum/green-building-techn...

Answered by Steve Knapp CZ 3A Georgia
Posted Nov 15, 2017 10:19 AM ET
Edited Nov 15, 2017 2:09 PM ET.


Thanks for your response, Steve. I’m not trying to convert my pole barn into living space. Just want to raise the temp a little during the winter months maybe 1-2x/week. I’ve searched the forums and haven’t found my answer yet, which is why I posted a new thread. Hopefully someone will have some insight on my specific building.

Answered by Doug Kremer
Posted Nov 15, 2017 10:44 AM ET
Edited Nov 15, 2017 11:05 AM ET.


I find it's easier to do searches using Google (green building advisor, [topic]).

The big issue with pole barns (and most retrofits) is air sealing. Here is how Martin Holladay summed it up in a recent thread:

As you probably know, the big problem with trying to insulate a post frame building is establishing an air barrier. T-111 isn't a great choice for siding, because (lacking sheathing) it is hard to air seal.

If you have the patience for a cut-and-cobble job, you are likely to have less air leakage than an approach that just uses batts. Although I generally try to avoid the use of spray foam, there is no doubt that spray foam would do the best job of air sealing. (If you go this route, you should specify open-cell spray foam or one of the newer environmentally friendly varieties of closed-cell spray foam.)

For more information on these options, see these three articles:

Cut-and-Cobble Insulation

Flash-and-Batt Insulation

Next Generation Spray Foams Trickle into the Market

I would urge you to fur out the stud space to bring everything even with the posts. The easiest approach would probably be to run some 2x6s through a table saw, ripping each 2x6 into two studs, each 2 inches wide. Install these new studs vertically, to reduce thermal bridging.

Read more: http://www.greenbuildingadvisor.com/community/forum/energy-efficiency-an...
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The cut and cobble method he mentioned would probably be the most affordable and effective approach (assuming you use reclaimed foam). Spray foam would be a lot simpler and faster though.

Answered by Steve Knapp CZ 3A Georgia
Posted Nov 15, 2017 10:58 AM ET


I did read that, but still doesn’t answer my question about my roof. That has to do with the wall and t1-11 (not steel). I’m not trying to heat my pole barn all winter long - just intermittently. Just want to insulate it enough to help hold some heat in, and avoid condensation.

Answered by Doug Kremer
Posted Nov 15, 2017 11:06 AM ET
Edited Nov 15, 2017 11:08 AM ET.


Doug, the way you worded the question sounds like you don't want to heat the building 24/7 to keep it at, say 40 degrees, and then take it to 65 when you want to use it. If you just want to apply heat when you use it, have you considered a woodstove, and skipping the insulation altogether? It's not exactly the green solution, but most of what you read on this site applies to spaces that are used more often than your proposed once or twice a week for a couple hours. Any expense and effort you undertake to insulate won't pay for itself, and the "green" perspective might suggest it doesn't justify the embodied energy and chemicals. Plus, any heat source properly sized for an insulated space will take forever to bring it up to temperature on a cold day. Without insulation, a woodstove won't heat the far corners but will have a nice circle of comfortable radiant heat to work in. With a can or two of spray foam, seal up obvious air leaks, although if the room becomes too tight your stove won't draft.

Answered by Andy Chappell-Dick
Posted Nov 15, 2017 1:58 PM ET


Andy makes a good point. A wood stove makes a lot of sense since this isn't your forever home and you only need heat periodically during the winter.

Answered by Steve Knapp CZ 3A Georgia
Posted Nov 15, 2017 2:12 PM ET


Anyone interested in Pole Barns might enjoy this video from 475: https://foursevenfive.com/475-on-site-net-zero-upstate-ny-passive-esque-...

Answered by Ethan T ; Climate Zone 5A ; ~6000HDD
Posted Nov 15, 2017 2:18 PM ET


You don't want to install fibrous insulation (like fiberglass) directly against the underside of your steel roofing, since steel roofing regularly gets damp due to condensation. The moisture will saturate the fiberglass.

If you got a "really good deal" on some 1.5 inch thick polyiso, that's the insulation to use. Install the polyiso on the underside of the purlins, and tape the seams with a high-quality European tape from 475 High Performance Building Supply. Install as many layers of polyiso as you can afford. Remember to finish off your work with a layer of 1/2-inch drywall for fire safety.

Answered by Martin Holladay
Posted Nov 20, 2017 7:27 AM ET

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