Confused on Vapor Barrier / Ceiling Insulation

[kmacht]

I need some help. Reading the recent posts here about various garage ceilings being insulated has left me confused. I have a 2 car garage with a gembel style roof and a 2nd floor and am located in Connecticut. Think 90 degrees in the summer and 30 degrees in the winter. I have turned the 2nd floor into a shop area with various tolls and workbenches up there. As money frees up I want to insulate the ceiling to help keep it warmer in the winter with a heater running and cooler in the summer. Being a gembel style roof, the ceiling makes up most of the side walls on the 2nd story as well. This makes the 2nd floor get quite hot in the summer when the sun is hitting the roof because all that heat from the black shingles radiates right through the plywood. My initial plan was to buy sone 24" wide fiberglass insulation that has the craft paper on one side. I was going to put the insulation between the rafters and have the paper side facing the inside of the building, stapled to the joists.

That leaves two questions. The first is, do I need to allow any sort of ventilation behind the insulation for the roof? In a normal attic you have soffit vents and ridge vents to help keep the attic cool during the summer time. I am concerned that if I put up insulation that it will ruin the plywood and roof quickly because the heat will have nowhere to go in the summer. If I do need some sort of vent then how do you do that without making the room cold in the winter as well?

The second question relates to the vapor barrier. My garage is essentially unheated. I have a torpedo style heater that I am going to use to warm the place up while I am working out there in the winter but when I am not in there, there will be no heat. In the summer I will probably put in an air conditioner. So which side do I put a vapor barrier on? In the summer the outside is the hot side but in the winter when I run a heater, the inside is the hot side.

Keith

 

[banzaitoyota]

Here is some interesting information:
http://www.energybooks.com/pdf/D1142.pdf

 

[HomeBrewA4]

you want kraft paper towards the inside.. putting it on the roof gives it a double vapor barrier and it will sweat and mold.

you will need to stick a proper vent where the insulation is going to be.. we do half a vent sticking out on both ends of the fiberglass for ventilation.

Also keep in mind that Kraft paper exposed is considered a fire hazard. If you're good with not covering it up for awhile, just make sure you keep an eye on it. IDK what a homeowners insurance policy would say if, god forbid, your house catches on fire, related or unrelated to that space and they see that.

Depending what your framing is, we stick whatever its framed out for. If its 2x8, that's enough for a vent and r19, just make sure you dont try to shove something bigger in it and crush the vent. The vents Lowes sell, we are forced to use through 1 of our builders due to their tie with the insurance companies. Anyways, they are brittle and collapse or break. Our vents we get from a wholesaler, we can stick a r19 and a venter in a 2x6 due to their design.