Barn remodel with metal roof

[Harkon]

Hi there!

Thank y'all for taking the time to read my post and hopefully sharing your thoughts.

I am in the process of remodeling my barn into a living/work space. It's a two story building and downstairs is done and turned out so great that I wanna do upstairs now, too.
It has a metal roof, soffits on side, ridge vent on top. 900 sqft.
NO wood between Metal and attic. Just bare metal sheets on 2x6 rafters.
The "attic" will be super small and not high at all. The highest place between drywall ceiling and ridge vent/top of the roof will be around 2-3 feet.

I installed extra 2x4 to hang drywall, so there will be some sort of "attic" space between the drywall and the roof at least towards the middle of the roof/room.
I was thinking to spray foam a little bit to the metal directly (already have two foam kits (Vega Bond V600 Closed Cell Spray Foam Fast Rise 600 Board Feet Kit)
in order to add some R - Value and to fight condensation. (and to seal the roof against leaks)

And then put regular fiberglass insulation between the extra 2x4s / above the drywall ceiling. So that would create some extra "attic"space towards the middle of the roof/room.

So, I am wondering basically two things:

a) will the foam be a waste as it does NOT add any insulation value as there are open soffits and ridge vent (ridge vent will be with these foam things in the shape of the metal rood to keep put critters and insects)

b) what are the alternatives?

Thanks!

 

[billconner]

Knowing what climate you're in would help a lot.

I think venting between the foam and fibreglass makes no sense. You want a clear thermal barrier. I'd do it all at the ceiling and vent the space between that thermal barrier and the roof. You could close the soffit and ridge vents an put all the insulation against the metal roof, but more potential for problems.

I don't think the diy foam idea is very often successful. Those kits are for gaps, maybe band sill, but not a whole roof. And definitely not a good or permanent fix for leaks.

 

[Harkon]

Hi Bill,

first of all thank you so much for your quick response! Much appreciated.

I am in Northern Florida.

So what you are saying is to leave the roof the way it is with open soffits and functioning ridge vent and just do ceiling insulation?

Will that also get rid of potential condensation on tye underside of the metal roof? As i don't want it to drip on the fiberglass insulation.

Thanks for all your input!

 

[billconner]

I don't know. If the venting works, it should keep the temperature difference between the metal and both attic and outside pretty much the same. But, zero experience and not much study of buildings in your climate.

I think you'd really like the foam or a vapor barrier on the top or outside of the fiberglass, since you're probably air conditioning interior space and you don't want moist exterior air condensing on cooler drywall.

 

[Hank11]

I think the batts as shown will help a lot. It won't be the highest R value, but the bang for the buck and effort is high.
Don't spray foam unless you can do the entire roof deck and close off the ventilation.