Vapor Barrier and Insulation in Ceiling?

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TheTooth

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To me, it still seems like if, in the ceiling or the walls, you have a vapor barrier against the warm space, then insulation then your green board or sheet rock, your gonna trap the 70% moisture in your storage room between the vapor barrier and the insulation. Won't that eventually destroy the insulation properties of fiberglass batting?
As I understand it, the moisture barrier is to avoid your scenario. Condensation appears on the warm side of an object (think of an operating propane tank or a cold glass of water or item taken out of a freezer). That is why you want the moisture barrier on the warm side of the equation, so that the moisture is kept away from the insulation that is on the cool side.
 

sly22guy

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How much of a temp difference are we talking about? if the house is 80 and the room is 50 ok vapor barrier. if the the house is avg 70 and room is 60 just insulate your joists. if you do go witha vapor barrier i would first insulate the area between the joists, then i would take firring strips ie 1x3's and run them across the bottoms of the joists, then staple your plastic to that you can tape the edges if you want, then i would just stick a sheet of 1/2" drywall or wanes coating or whatever you want to use for your ceiling. vapor barrier between floors is not as critical as walls. if you are finishing a basement typically you put your vapor barrier up then use a foam insulating panels then frame then drywall. id just take an average of you temperatures and see if it is really necessary.
 

Dugger

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Dinolan - I take it you are only interested in insulating the storage room since it will be kept at 55 degrees and 70% humidity and the making area will be more or less room temperature. I'm a little out of my expertise here, but I don't think the humidity in the storage area will condense at that low temperature - it's warm moist air that gives up its moisture when it hits a cool surface. So I believe the barrier on the warm side is what is needed. However, to hedge your bets, I still suggest rigid foam on the joists to provide a barrier to both sides, with no fiberglass to worry about.
I wouldn't worry about any moisture created in your making area - that will simply migrate through to the upper living area at relatively the same temperature. You will, however, face the same problem on your walls of the storage area.
I must say again that I am certainly no expert at this and you will probably benefit from talking to someone who has actually done this, as I believe you intend to do.
 

mmadmikes1

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Most of the humility in the air in Houses is produced by humans. If you are looking for a continues 70% humility you will need to use a vapor barrier paint period, most moister damage happens to Drywall in form or deadly mold. If you put vapor barrier behind drywall and then keep room at 70 % mold had a perfect place to grow. Super SpecLatex Vapor Barrier/Primer Sealer 260 from BENJAMIN MOORE is what we have been using. We have torn down whole building because of drywall mold. There is no need to go to a spendy rigid insulation unless you have a clearance problem and need the extra R-factor. Fiberglass will work fine. Floor joists always have enough room for R-19. Walls in older houses with 2x4 construction can use rigid to get to R-19. Also remember to get an insulated door. Cheap home depot door will counter all work to maintain room environment
BTW I did put up vapor barrier because I chose to do my walls and ceiling in T&G cedar siding. It is a great look
 
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