I'm building a room into our (existing) barn; how should I best go about insulating it?

The barn is a Morton building -- pole barn construction, metal siding. It's closed on three sides but open on the fourth, so it's not as much a closed-in building as a glorified run-in. The room I'm building will be against one corner, so two sides are defined by the walls of the existing barn, and the other two sides are framed up and built inside the existing structure. The floor of the room is a concrete pad; the rest of the barn is a dirt floor.

I'd planned on doing standard kraft-faced fiberglass, just like I'd do in a house. However, I've read that the moisture in a metal building can build up on the insulation and cause it to mold. I've certainly noticed that on certain days there's plenty of humidity that builds up in the barn (enough to cause water to condense on the inside of the metal siding).

So: is the fiberglass a bad idea? If so, what should I do instead? Should I do a moisture barrier on the outside of the room (between the framing and the metal barn sides)? Or...?


The links in the other answers are very informative!

In answer to your question:

So: is the fiberglass a bad idea?

The answer is yes, at least in the exterior walls.

In answer to your question:

If so, what should I do instead?

You have a bunch of options, none as cheap as simple fiberglass batts. My personal recommendation would be rigid foam on the exterior walls and ceiling with fiberglass batts on the newly built walls. Pricey but effective.

Essentially, you're going to be building a little tiny insulated house inside the barn without the need to weatherproof it. At the risk of losing a few square feet of floor space, why not just build the room free-standing in the corner, with maybe a couple of framing attachments (e.g. longer ceiling joists) to the barn walls? That way you can do a simple wall with sheetrock both sides and fiberglass insulation in all four walls and the ceiling.


Sounds analogous to insulating the interior of a basement wall. Rigid or spray foam next to the metal, then a stud wall with drywall, according to here: http://www.greenbuildingadvisor.com/blogs/dept/musings/how-insulate-basement-wall

  • Answers that rely too heavily on content from an external link, become useless if the link ever dies. – Tester101 Dec 18 '12 at 17:34


This article seems to indicate that a product called "Prodex" isn't affected by humidity or water.

  • Answers that rely too heavily on content from an external link, become useless if the link ever dies. – Tester101 Dec 18 '12 at 17:33
  • Fair enough. The basic idea is that it isn't susceptible to deterioration by heat, and its insulation properties aren't affected by humidity, as it also serves as a vapor barrier. – Justin Abrahms Dec 19 '12 at 9:54

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