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Foam, Dehumidifier & Garage Post New Topic | Post Reply

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Dennis Oakes
Posted: Oct 05, 2014 05:27 AM
Foam, Dehumidifier & Garage
I'm having an intense discussion with my builder on the placement of the dehumidifier. Open cell foam has been installed on all rafters to include the garage. Currently, there is a foam wall built between the living area and the garage of which he plans to cut two large holes to allow the attic air access to the dehumidifier that will be installed over the garage. The builder has no plans to install insulation in the ceiling of the garage (floor of the attic). To me, it seems insulation would be installed on the garage ceiling to complete the insulation envelope of the house otherwise, there is only 1/2 inch drywall. Moisture and heat will make its way through the garage ceiling defeating the purpose of the insulation envelope. The builder insists he is correct in not installing garage ceiling insulation. Thanks for your comments.
Posted: Oct 05, 2014 09:24 PM
Are the garage exterior walls insulated?
Dennis Oakes
Posted: Oct 06, 2014 04:40 AM
There is no wall insulation in the exterior walls of the garage. There is insulation in the wall adjacent to the garage and the living area.

My limited understanding is two large holes in the attic foam wall. Then again, there could only be two ~16' holes with one drawing air from the living space attic and one for a return. This latter makes more since as the installation involves an AprilAir unit.

Mark Mouton
Posted: Oct 06, 2014 09:52 AM
What city and state is the house located?
If it is in hot humid, Don't bring garage attic into conditioned space, keep the attic wall separating conditioned attic from unconditioned intact and ventilate the garage attic (ridge vent or whirly bird).
If A/C is correctly sized,(not oversized) you don't need a dehumidifier.
And you are correct about the ceiling needing to be insulated to complete the envelope (if you bring the garage attic into conditioned space), which I don't personally like to do.
mark moyer
Posted: Oct 08, 2014 07:25 AM
dont draw garage attic air into a home,,ever,,anywhere...
Dennis Oakes
Posted: Dec 21, 2014 10:03 PM
Location is NE Florida.

Note about finished insulation. To install the whole house dehumidifier (not sure I really needed this but with open cell, the builder and HVAC company talked me into it) a 4 foot x 5 foot whole was opened in the foam wall that divided the garage from the living area. So much for the two 16" holes for the dehumidifier ducts.

I can do two things.....1. Hire an engineer to attest that the garage ceiling needs insulation at ~$250 or 2. Insulate it myself. Question is can I get away with bat insulation or should I go with something else? And if I use bat insulation, which side does the vapor barrier go? Towards the attic side?

Mark Mouton
Posted: Dec 22, 2014 10:56 AM
From what I can understand you explained, they want to install the dehumidifier in the area that doesn't need to be dehumidified.
And then try and dehumidify the the living area of the house through the sheetrock ceiling of the house, which it will do.
So if moisture will move through the ceiling of the house, what is going to keep it from coming through the ceiling in the garage?
The dehumidifier needs to be installed in the conditioned area of the house, attic or living area, and plug up the 4x5 hole.
You SHOULD go to the engineer.
Dennis Oakes
Posted: Dec 22, 2014 07:39 PM
Billygoat, thanks for your interest.

The dehumidifier is installed over the garage and the duct work for this is passing through the large hole that was cut in the foam wall separating the garage and the living area attic space. This large hole, in my opinion compromises the integrity of the closed attic system when the garage ceiling is not insulated. The dehumidifier duct work is connected to the house HVAC duct work removing humidity from the living area not the attic. A thermostat with humidity control is used to cycle the dehumidifier utilizing the HVAC fan.

I found an ICAA engineer who I plan to call to inspect the installation and make recommendations.

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