Roof Condensation, Shop Insulation question

Hey All,

I am in the middle of redesigning my shop. I’m drawing out the electric and studs, planning for insulation, etc. The shop will be heated and cooled. I’m writing this post in hopes to solve a potential condensation issue.

The issue that I’m running into is the roof. I want a vaulted ceiling in my shop. I would like to insulate between the rafter perlins that hold the metal roof on, but I’m afraid of putting fiberglass batting right against the roof. There will be a metal roof, 2×4 perlins with insulation, and then alluminum sheeting on the inside of the shop.

I am afraid that this method will not be adequate enough, and it will eventually draw condensation on the inside of the shop, under the metal roof, and soak the insulation (then drawing more condensation due to lack of effective or wet insulation, etc).

Would it be better for me to drop below the bottom of the perlins, and stud in 2×6 rafters that will hold the 2×6 fiberglass batting? It would be the metal roofing, 6” of air void, 6” of insulation, then the alluminium sheeting for the interior finish.

Will this be enough for air to move if I vent it on the ridge, and on the gables through vented sofit to avoid any condensation? The drip edge has no vent.

I am really perplexed by this… I would really like to plan and begin rough design of the interior, but I don’t know where to begin with this roof.

I have thought about having a professional use spray foam, but I still don’t know if it would be enough (and I’m having trouble finding someone in my area). The last thing that I want is to have a moisture issue in the shop after I’ve worked so hard to prevent it. Since the ceiling is vaulted, I don’t think that loose, blown in insulation won’t be an option because I think it would settle to the bottom over the years, creating condensation at the peak.

Putting a flat ceiling in my shop isn’t really an option for me, I need the working height that the vaulted ceiling provides, or that would be an obvious answer for me. A flat ceiling would give me less than 7’6”.

Thoughts?

Thank you all in advance for ANY help or thoughts that you can provide….

Steve.

-- --Steve