Garage ceiling insulation question

[NJMatt50]

Hi, I am insulating my detached garage roof. Its a flat roof with 2x12 beams across. I am putting R-30 in between the joists. I am going to put 6mil plastic sheeting below, fastened to the joists, nothing else. I will be heating this off and on while out there. Do I need some kind of venting between the plastic and the roof materials? There will be about a 3 in air gap between the insulation and the roof. I have soffits on the side but the seem to be blocked from the where the walls meet the roof. Thanks.

 

[GaBull]

Flat roof, with insulation against the roof decking and plastic sheeting on the paper side of the insulation facing the inside of the garage. If this is true I would put the styrofoam air channels in between the roof decking and the r-30, make sure they extend to the soffets. This insures there is air flow between the fiberglass insulation and the roof decking.

You can also call a local insulation company up there and ask the regulations.

 

[NJMatt50]

Well the insulation is not against the roof decking. I have 2x12's with 9 1/4 thick insulation. Also using unfaced insulation. Do you think that the 2 3/4 inches of gap between the insulation and roof decking is enough to move air? As long as there is some room between roof deck and insulation is that good enough?

 

[bazzateer]

Hi, I am insulating my detached garage roof. Its a flat roof with 2x12 beams across. I am putting R-30 in between the joists. I am going to put 6mil plastic sheeting below, fastened to the joists, nothing else. I will be heating this off and on while out there. Do I need some kind of venting between the plastic and the roof materials? There will be about a 3 in air gap between the insulation and the roof. I have soffits on the side but the seem to be blocked from the where the walls meet the roof. Thanks.

Sounds good to me. I#ll be doing much the same with my garage once it's built.

 

[socapots]

i recently put up some insulation in a shed, I had to put string (used some wax coated stuff) to keep the insulation up. Wasnt to much of a pain. And this way i know there will be virtually no weight on the vapour barrier.