Insulate over girts or between them?

Hindsight is 20-20.. I have a post frame building that was built in 2003 on a concrete slab. Looking to create an "office" inside that will be heated/air conditioned If i knew then what i know now i would have had Tyvek and foam put on the exterior before the steel went on, but that is not the case...

Soooo my plan is to install rigid XPS foam on the inside of the exterior wall, then frame next to that and fill wall cavity with R19, cover with Visqueen vapor barrier and then/drywall

My question is do i place the and seal the rigid foam between the 2x6 girts, or put them on top of the girts then build my conventional wall system? Either way there will be an air space between the exterior wall and conventional wall system.

Spray foam is not an option....

Thanks..

When I built my pole barn (in Whitehall, MI) I used 1.5" Styrofoam between the girts and then added 1" foam over the whole wall. Then I put 1/2 drywall over the whole wall between the posts. This with 2" of Styrofoam on the ceiling kept everything toasty by Lake Michigan. It's a lot cheaper than your method and faster too.

A continuous layer of the foam insulation is going to be more effective than the surface being broken by the 2x material. So if you have the option and space to accommodate it that way, you'll have a better end result relative to insulation effectiveness.

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Originally Posted by Chris Damm

When I built my pole barn (in Whitehall, MI) I used 1.5" Styrofoam between the girts and then added 1" foam over the whole wall. Then I put 1/2 drywall over the whole wall between the posts. This with 2" of Styrofoam on the ceiling kept everything toasty by Lake Michigan. It's a lot cheaper than your method and faster too.

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Great idea...That why i love this forum.....

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Originally Posted by Jim Becker

A continuous layer of the foam insulation is going to be more effective than the surface being broken by the 2x material. So if you have the option and space to accommodate it that way, you'll have a better end result relative to insulation effectiveness.

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Excellent advice.... I am gonna do as Chris says... and then put a continuous layer on top! The money i save on the studs and batt insulation will allow me a lil thicker foam on top of the girts! :-)

D

Yes, Chris's suggestion is really good because it fills up the wall and having "some" foam between the girts is a lot better than "none" behind them! It doesn't raise your cost a huge amount, either.

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Originally Posted by Jim Becker

Yes, Chris's suggestion is really good because it fills up the wall and having "some" foam behind the girts is a lot better than "none" behind them! It doesn't raise your cost a huge amount, either.

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i think you mean "between" the girts?

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Originally Posted by David Ruhland

i think you mean "between" the girts?

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Yup...that right there is a "fat finger"... LOL Sorry about that... Fixed it.

Here's another idea for you. My shop is a pole type construction building. Over the purlins, is 2" ISO board with the edges sealed to each other with spray foam. That gives you an R12. I then ran purlins on the inside of the poles and sheeted over those. Finally, the walls have blown in cellulose. That is R19ish. The whole package ends up being about R30 or a little more. Because it has purlins, instead of studs, the cost of the lumber is quite a bit less and it takes minimal time to frame.

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Originally Posted by Lisa Starr

Over the purlins, is 2" ISO board with the edges sealed to each other with spray foam. I then ran purlins on the inside of the poles and sheeted over those. Finally, the walls have blown in cellulose.

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So if I understand correctly... you have boards running horizontally from pole to pole, covered with osb, plywood, etc the space behind is blown in insulation? Did you blow it in yourself? Do you have a vapor barrier? Any pics? Thx

Think Morton buildings is doing something similar to Lisa's.

David, Yes you are correct. The 2 x 4's run horizontally, between posts. They are on 2' centers. The foam, since it is sealed, acts as the vapor barrier. Additionally, because it is on the outside purlins, there is an air space behind the foam for ventilation. Yes, my DH and I did blow the cellulose ourselves. I'll try to locate the photos and post.

I am soon undertaking a similar project. My building is still bare frame and walls. My intention and still is at this point is to put plastic sheeting up as a vapor barrier before anything else. This way moisture can't pass through to the cold steel and condense and cause major problems. Then I was going to "bookcase it like Mike Hedrick did on his building. Then use R-19 kraft faced fiberglass in the walls. I could use 1-1/2" foam board between the purlins before adding the fiberglass. I already have the fiberglass so that's going in regradless of any other steps I may take. I'm not trying to hijack the thread. This just seems like very similar needs. Am I on point using the plastic moisture barrier to keep from having problems with condensation on the inside of the metal siding?

So my understanding of Lisa's build is 2x4s horizontally with 2" closed cell foam pushed to the outside and sealed with Great Stuff or similar then drywall. That leaves air space on both sides of the insulation.

This sounds good, 2" of foam is plenty and there is room to run wiring behind the drywall.

It may require some shims between the poles and the 2x4s to get a flat wall.