Garage Heat Out of Control!!

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Old 06-13-10, 10:06 AM
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Unhappy Garage Heat Out of Control!!

Help! The summertime heat in our garage is miserable, and I would appreciate any suggestions where to start improving the situation. We live in a coastal region of SC, and it is not unusual for the garage temp to exceed 100F by noon. I'm not looking to create a comfortable working environment in the garage, just tolerable temps that won't turn rolls of tape into solid, unusable lumps.

Our single-story house is built on a slab, with a small storage attic above the garage. Although the garage is attached to the house, the attic area above the garage is closed off from the overhead area for the remainder of the house, which is insulated. Rooms interior to the house are comfortable and seem to be adequately insulated.

Garage walls and ceiling are finished, with fiberglass batting insulation in the walls, but no insulation above the garage, between either the ceiling joists or rafters. The garage is very small, with room only for narrow shelves on each side, then two cars. There is a distinct increase in garage temps whenever a hot car is brought inside, which made me question the benefits of adding overhead insulation. The overhead eaves are well-vented, and there are no signs of moisture problems.

Do I insulate the attic or not? Between ceiling joists or rafters? I'm also open to the option of some type of exhaust fan, either directly in the garage or attic, if it will help my situation. Building codes take into account hurricane concerns, so I'm not sure what is allowed regarding wall/roof openings for fans. Where do I start? Thanks for your help.
 
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Old 06-13-10, 11:49 AM
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I would opt for a continuous ridge vent with soffit vents. You must move the air above the garage to keep it from opressing down on the garage. Insulate between the ceiling joists with R25 or so and move the air above it. Don't let your insulation loft up too much to prevent air movement. Use Owens Corning insulation baffles to prevent that.
 
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Old 06-13-10, 04:37 PM
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Chandler - Thanks for your response. The soffit vents and a full-length ridge vent are already in place. I was concerned that ceiling insulation would trap heat in the garage, but I guess that's a dumb concern at this point. Thanks for mentioning the baffles, I would have missed that.

Moisture has not been a problem in either attic or garage, so is there any need to consider faced insulation for this job? Thanks again for your help.
 
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Old 06-13-10, 07:16 PM
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Yes, if you use batt insulation, put the paper toward the garage, or "down". You have to separate the temperate temperature of the garage from the unreasonably hot "attic" heat, and allow the fresh air from the soffits to evacuate it through the ridge.
 
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Old 06-14-10, 08:21 AM
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Thanks again for your help. Looks like it's project time.
 
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Old 06-15-10, 10:57 AM
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I would check to make sure your venting system is working as designed. A lot of times good intentions don't add up to good execution.
 
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Old 06-17-10, 07:30 AM
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If you are in the garage alot and need it as cool as possible, I'd start by installing attic foil first. Radiant Barrier Foil Insulation Do-It-Yourself Radiant Barrier Tips This will keep most of the heat from radiating down into the attic space and insulation. The foil is superior to the rad. barrier paint. My attic only gets 110* in the summer.
After you get the garage done, do the remainder of the attic...
as it also lightens the load on your a/c ductwork.
 
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