Hello,
We are going to build a 40×48 steel pole barn.   I am going to frame out about 1/2 of it as a living space while we build our home on the same property.

It will be a permanent living area as we will always keep it for guest and friends family so I do want to build it well.

Is spray foam good enough on the walls to create the vapor/air barrier? (closed cell).

I have had one insulation contractor suggest and quote me for open cell foam and I know it does not act as a vapor barrier.

Should I install a stand alone vapor barrier on the outside prior to installing the metal siding?
Climate zone 6.  Low wind area, surrounded by full growth hardwoods.   Morning sun, afternoon sun, that will mostly be on the south side of building about 4 months of the year.   Hot & humid in the summer 90/95 with 85 ish percent humidity and winters that average 2 feet of snow, frost that carries 12 inches and an average temp of 20F.   We do get into the -20s.

THank you!