Detached heated garage - do I need a vapor barrier?


Old 11-09-18, 08:38 PM
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Detached heated garage - do I need a vapor barrier?

  • Climate: Chicago, 0-35 degree F winters.
  • 2-car detached wood-framed garage, unfinished, concrete slab.
  • Pyramid hip asphalt shingle roof, plentiful ventilation through soffitt vents and roof vents.
  • Installed a natural gas ceiling-mounted blower heater, will be running about 50% of the time, possibly 100% if gas bill doesn't get too high.
  • Planning on blown fiberglass insulation in attic, fiberglass kraft-faced batts in walls, 1/2" drywall over everything.

My question is, do I need a plastic vapor barrier on the ceiling in between the drywall and the framing? I've read that you should ALWAYS use a vapor barrier and that you should NEVER use a vapor barrier in similar situations...grrr.

Please advise, thank you!

Last edited by swedespeed7; 11-09-18 at 10:48 PM.
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Old 11-09-18, 11:26 PM
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Current convention is not to use a vapor barrier. That said, air sealing before installing the insulation can do almost as much as the insulation itself. Personally, I prefer mineral wool to fiberglass.
Old 11-10-18, 04:22 AM
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A little late I admit, the critters do not have any love for rock wool( wear a mask when you install itas with fiberglass)
One problem with an unheated garage would be "sweating" when humid warm air was introduced to the structure, we have a similar situation as yours and I left the vapor barrier on and have had no problems.
Consider this( I know its late) treat one wall differently than the others and see if problems develop.
Old 11-10-18, 04:40 AM
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Unless you have a way to manage moisture in an enclosed space never use plastic, it will completely trap moisture which can lead to water/mold issues.

All houses need vapor barriers, this slows down the transfer of moisture but does not block, big difference.

However, you are insulating a garage with huge doors with big gaps so the issue is sort of mute!
Old 11-10-18, 05:20 AM
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Got it - thanks guys!

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