Metal building living space ceiling insulation

[titus211]

Sorry if this has been answered before - my search-fu on the forum didn't find much that was helpful.

I have a 40x60x16 metal building on slab that I'm wanting to convert an upstairs area to a living area. Currently the construction is typical I-beams running north/south, with 2"x8" C-purlins running on top perpendicular to that. There's about 1-2" of closed cell foam sprayed on all of it.

To close in and make an air conditioned space under that, I'm thinking of using 6" blanket insulation (about 4' wide) running between the purlins, hold it in place using metal straps or similar. Then place a layer of 1" rigid foam insulation, and then add metal of some sort (probably CF panel).
I'm taking this approach because I'd like to keep as much vertical space as possible (not lose it to additional ceiling structure), and I'm afraid extra wood strips+drywall would be too heavy to add on to the ceiling.

Is this a completely insane approach? Suggestions?


EDIT: dagnabbit, meant to put this in the General Garage Discussion - somehow I'm in General Tools. Can I move it or does a mod have to step in?

 

[Voi]

Sorry if this has been answered before - my search-fu on the forum didn't find much that was helpful.

I have a 40x60x16 metal building on slab that I'm wanting to convert an upstairs area to a living area. Currently the construction is typical I-beams running north/south, with 2"x8" C-purlins running on top perpendicular to that. There's about 1-2" of closed cell foam sprayed on all of it.

To close in and make an air conditioned space under that, I'm thinking of using 6" blanket insulation (about 4' wide) running between the purlins, hold it in place using metal straps or similar. Then place a layer of 1" rigid foam insulation, and then add metal of some sort (probably CF panel).
I'm taking this approach because I'd like to keep as much vertical space as possible (not lose it to additional ceiling structure), and I'm afraid extra wood strips+drywall would be too heavy to add on to the ceiling.

Is this a completely insane approach? Suggestions?


EDIT: dagnabbit, meant to put this in the General Garage Discussion - somehow I'm in General Tools. Can I move it or does a mod have to step in?

I have a couple of concerns. One is having a moisture trap between the spray foam on the roof deck & the 1" rigid foam. I believe poly iso is the most vapor open rigid foam so if you do go this route it might be your best choice.

Second would be dew point control with such a thin layer of closed cell. This is not as big of a deal in Texas as it is further north so I'm not sure what to recommend.

You might also get another set of opinions over on Green Building Advisor.

 

[Old Man Roger]

I've seen companies that sell metal building houses. Maybe see what they use?

 

[titus211]

I see some people using all closed cell foam. I could have up to 8" of that which would provide R50+ and not use the rigid foam board. Not sure how expensive that would be. Any ideas if that would cause vapor barrier or moisture issues?

 

[scubadoober]

Spray foam.

 

[Voi]

I see some people using all closed cell foam. I could have up to 8" of that which would provide R50+ and not use the rigid foam board. Not sure how expensive that would be. Any ideas if that would cause vapor barrier or moisture issues?

You wouldn't have to do all closed cell - you could also do a combination of closed & open to save some money.

In your climate you might even have sufficient closed cell already for dew point control.