Red iron building insulation questions

[breynolds]

Hoping someone can give some insight on whether this is an ok idea or not. I have a red iron type building. Had a quote for spray foam last year and it is more than I’m looking to spend, had insulation company do quote on silvercote type as well but being girders are all not the same size an kind of odd ball size that came out even more costly than spray.

So my idea is would it work if I ran 2x4 in between my girders flush and then rolled in 23” r19? I will put up tin when finished so no concern of fire hazard. Concern a question is girders are 7-1/2” wide would the 1-1/2” gap between insulation and outside tin cause problems. Do I need to install plastic over insulation on warm side even though it would be faced, no insulation expierence just looking for inexpensive way to DIY.

 

[My Old Tools]

I did that in a barndominium that I lived in for 10 years. The building was fiberglass roll insulated when build. Then I did 2x4 stud walls inside and recessed them inside the I-beams and girts so that the sheetrock would be flush with the beams,. I roll insulated the stud walls independent of the shell insulation already in place.

 

[StefanNH]

You'll want a vapor barrier as the tin on the outside probably isn't air tight. I'm putting up my building and the insulation gets roll out before the tin so it's in direct contact with it, with a vapor barrier facing the inside. If you don't put a vapor barrier you will get condensation on the back of that tin and mildew on the insulation.