It depends on your town building codes. I couldn’t shut off my loft because then it would be considered a bedroom (even though there were no closets).

We need 10,000 sq ft of land for each bedrorom. So, check with your town’s building dept.

^^^ That reads like the beginnings of another ridiculous rumor started by Houzz. Closets never were required for bedrooms, and I suspect that it is not the 10k sq. ft. of land for each bedrorom that is the actual requirement, but that you are required to have a sufficient amount of drain field from your septic tank for each room that could be considered a bedroom. If you had an extra 10K feet of swamp land, it would not allow you to have an extra bedroom, and soil with a better perk test would make for a far more efficient drain field, needing less space.

What do you use the loft for? Any pics of that space? And the horizontal railings will definitely be used as a ladder, even on the stairs. So you would still want to use some of the clear plastic sheeting there.