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Old 05-27-2009, 01:32 PM   #1
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Basement Garage with Concrete Slab: To Vent or not to Vent


We are in the North GA mountains where the summer is extremely humid and can be quite warm. The winters are cold and generally low in humidity. Our problem is the summer months mostly in our garage, not so much the finished basement.
Both have concrete block walls and concrete slabs.
Each have one wall that is below grade.
The garage has a heated/cooled living space above it.
The garage does not have conditioned air.
There are no foundation vents in the garage
The air is extremely musty in the garage.
There is a problem with green mold which finds a home on sandply stock (cabinet-making wood stock) which is exposed, sitting on-end on the garage slab.
I have not seen mold on the joists, just that wood that touches the garage floor for about three feet up.
This is where the controversy begins.
One expert says do not to put in foundation vents,
another says to air condition the space,
one says to put foundation vents in,
one says to put in a dehumidifier,
one says to finish the garage with insulation on the walls and paneling.
Air conditioning doesn't make sense to me because the space is already cooler than the rest of the house, and we only run our A/C perhaps four weeks an entire season.
A dehumidifier would cost an arm and a leg to run, as it would be on 90 percent of the time during the summer.
Finishing the space doesn't make sense if most of the moisture is coming up the concrete slab.
What to do? Thanks for your input and help!

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Old 05-27-2009, 10:17 PM   #2
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Basement Garage with Concrete Slab: To Vent or not to Vent


I would put 1' of foam board on the below grade walls, then wallboard. Cut a high and a low vent in the walls, on opposite ends of the space. Similar to FHA's requirements in garages, 35 years ago. Try to get some air movement to reduce the moist, stagnant air. Leave it natural, unless you live in your vehicles. Seal the concrete slab with a quality sealer. Be safe, G

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Old 05-28-2009, 08:34 AM   #3
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Basement Garage with Concrete Slab: To Vent or not to Vent


Dear G:
Thanks for your posting. What type of Wallboard do you install if you were me? We assume the paperless type, or a PVC-type wallboard?
And, what type of concrete sealer might you suggest? Thank you.
N-GA
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Old 05-29-2009, 06:13 AM   #4
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Basement Garage with Concrete Slab: To Vent or not to Vent


Cool masonary surfaces and high humidity equals condensation, which gives rise to mold/mildew. To test for hydrostatic water pressure under the floor, tape a 16" piece of aluminum foil or plastic to the floor, seal all sides. Check after 2-3 days, if dry, you cna do most anything you want with the floor; damp, you have a small problem and the floor will need special treatment for any type floor covering; wet, forget it, major work to instll floor coverings. Wall can be insulated with rigid foam, but it must be covered with drywal for fire code. Owens Corning, the pink stuff, has a 2" foam with slot in the panels for furring strip. Tapcons secure the foam/furring strips to the walls, and yiou can install drywall directly to the furring strips.

Ventilating a garage can be tricky, depending on fire codes. Wall openings between living space and garage are carefully regulated to prevent fire travel. I found nothing in IRC about openings to the outside, provided there are no combustible materials around the opening. So a vent fan to the outside might be OK, check local code.

Last edited by Just Bill; 05-29-2009 at 06:19 AM.
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