Garage Ceiling - Help Needed!

[kbaum187]

My Husband and I are moving our t-shirt print shop to our home garage. We had a heater installed last week. It’s critical we keep the inside temp at 65° for the printing machines. We have insulated the walls. We are stuck on the ceiling. We want a way to insulate it and add some R Value, but we have no way to ventilate. Our garage was built in a way that makes it impossible to vent out. If we left it exposed there is just too much heat loss. Any suggestions would be greatly appreciated!!

 

[DGersic]

I have a flat roof, with t&g planks. I’m considering using 2” foam board for the insulation.

 

[kbaum187]

Would you install the foam board to the actual plywood, or install to the joist?

 

[The Cobbler]

spray foam under the roof deck, no vapour barrier or ventilation req'd then

 

[red]

Would you install the foam board to the actual plywood, or install to the joist?

It could be done both ways. Typical way to to cut the foam to fit between the rafters (joists). Personally that's how I would do it with leaving a inch air gap between the plywood and the foam.
You might want to consider using Rockwool comfort board. Water doesn't affect it and it's as close to fireproof as you can get. Basically burns at it's melting point.