I live in northern Wisconsin and am getting mold on my ceiling in my 900 sq ft. garage. The garage is a dry walled and has r19 in walls with plastic barrier over the insulation between the dry wall and insulation. Same goes for the ceiling has drywall , plastic barrier then r40 blown in over top. I am getting mold on the ceiling only every now and then where do you think my problem is ocuring from.

  • What is the R19 insulation made from? Is there a source of warm, humid air in the garage? Commented May 16, 2017 at 1:01
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    When did it start? What time of year? Is there a water source in your garage? Does your car have A/C? Commented May 16, 2017 at 1:26
  • Do you heat the garage? Does the roof leak (or - does the mold happen after lots of rain, since it might be a small leak into a lot of insulation and this not so obvious as a leak)
    – Ecnerwal
    Commented May 16, 2017 at 1:36
  • When mold shows up, see if the area actually feels wet. I agree with Ecnerwal that this sounds like it might originate from a leak. Water can follow very long paths from an entry point to where it gets into stuff. You can also get dripping from condensation on ductwork or overflowing condensate from an attic HVAC unit. If the mold is only on the ceiling, it suggests that the moisture might be coming from the other side rather than collecting from sources inside the garage.
    – fixer1234
    Commented May 16, 2017 at 16:37

1 Answer 1


If you run the engines of the cars in your garage then that is probably source of the high humidity and the moisture. If this is the case, then you need to vent that area when the engines are running and for a short time after the engines are shut off. Burning fuels create a lot of water vapor. If it is not from the cars engines, Then i would check for water infiltration from the roof area. With all that insulation and the vapor barrier you have created a tight atmosphere in the garage. Any operation in the garage that gives off moisture will allow that moisture to collect on the ceiling and walls which can allow for mold to grow.

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