Best way to insulate sloped attic ceiling for cannabis grow?

[KONY]

Want to have a veg space in attic space of a garage. I've researched insulating it and seems there are bunch of different ways including old fashioned vented, and newer methods of non vented.

My question is non of them take into account the humidity from growing?

Can you still do an unvented insulation and be okay with growing? I assume as long as you have dehumidifier or a/c or both it's fine?
I'm thinking 4" of spray foam right against the sheathing, then 4" of fiberglass bats under that to save on cost?

 

[NoSativaction]

Venting is to keep the sheathing/roofing material cool, not the attic space. Extends material life, but will also lower temps a bit inside if done right.

If you use spray foam, 2/3 of the total R value would need to be foam. Otherwise you will start getting condensation buildup between layers leading to mold. Foam doesn't stop air, it just slows it down. So say if going for R21 total, R14 of that would have to be foam. Almost pointless. Bite the bullet on cost and keep building up foam layers.

Look at woolrock insulation. Better R value per inch and water just beads up on it, doesn't penetrate the material.

Or build pseudo tents up there using extruded foam panels and pump cool air into them.

 

[prune]

If it's your house I would use through venting along the under deck from eave to ridge, to protect against humidity and heat damage. Cap that with your choice of fill insulation (batts, spray or blown) and then sheath the rafter bottoms with foam panels before covering with sheetrock or appropriate capping.