Roof insulation Question

[powellscooter]

Ok I have been searching and reading on this subject without finding answers and have a few questions.... I have a 11x37 carport that is attached to a mobile home that I converted to a shop/gym/bar. I enclosed the carport with 2x4 frame and siding, with garage doors on each end. I insulated the exterior wall and want to do the celing. Roof is the same construction, 2x4 with a plywood covered with rolled roofing and elastomeric coating, slight slope.
NOW TO THE QUESTION ! Can I insulate the roof/celing with fiberglas with a kraft paper facing? After insulation I will cover the walls with 1/4 melamine. I live in the high desert of Arizona little rainfall, low humidity. I keep hearing about mold issues and air space etc. I use a salamander heater to knock the chill off on winter nights. I think insulating it in this way should be fine but would like to hear others thoughts. Thanx!
Heres a link to some pics. http://www.garagejournal.com/forum/showthread.php?t=15213&highlight=powellscooters

 

[powellscooter]

Nobody? Oh well Ok.

 

[vartz04]

You need an airspace. And venting.

 

[Hotrod barn]

Does this area have a ceiling ,or are you insulating the roof trusses? If roof is what you doing you will have to allow for some air flow above the insulation.you will need a ridge vent and vents along the soffit.hope for some more response from other GJ members in your area of the country.colder than **** here right now,25 in my barn right now...maybe 15 outside.

 

[Chris705]

My $.02.....

Sounds like you want to insulate to keep space comfortable. Given your space is small, not exactly air tight (two OH doors). I would not think mold growth to be the main concern here with your question, but longevity of your roofing material. Rolled roofing (assume granular rolled roofing) with an applied elastomeric coating could suffer w/o the air space and proper venting to keep roof deck cool, if you insulated directly to underside. However if longevity of the roof is not your primary concern I would say go for it.

 

[pattenp]

How about using rigid foam board? Place it right to the underside no air gap needed. A couple of layers, 2 inch plus 1 1/2 inch should give you about R22. The down side is it's $$$.

 

[38Chevy454]

You do need an air gap. Since it sounds like this is trying to be a simple project, how about this for an idea: put a ceiling in that is flat, use 2 inch thick rigid foam along the bottom of the flat ceiling. Yes it requires a few more 2x4's to frame out. Then cover with your same 1/4 melamine. This leaves an triangle shape air gap between roof and the rigid foam. You still need some way for the air to escape from the space, so the slope on the roof, with the flat ceiling give a triangle space of air. Put a vent at one end and a powered fan at other to draw air through. Just removing the extra hot air in that space will make vast improvement for summer heat. Seal up the area good to hold heat in winter.

You could also put the rigid foam against the bottom of the roof joists, but you need some venting like a ridge vent which it sounds like you do not have.

 

[Gunnert]

Don't know about Arizona, but in Virginia you don't need an air gap in the garage. You can attach directly to the roof... Air gaps and ventilation codes are based on houses with kitchens/bathrooms, e.g. humidity sources. Your're fine to install as you suggest. My .02...

 

[powellscooter]

Thanks all !