Garage is too Hot!!

Old 08-23-16, 11:25 AM
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Garage is too Hot!!

I have a similar situation to the thread below called, "Converted garage is too hot!". Except its not a conversion, just a plain old two car garage with no ceiling (just like in the pictures). The rafters are 2x4's, 24" on center. If I staple standard fiberglass roll insulation (R-15, normally used in 2x4 walls), will that even help or would that just be a waste of money? Is there an easy way I can put thicker insulation here (say R-30 attic insulation), even though its only 2x4?

By the way, the garage door is insulated already, so not much more I can do there. Any ideas to help cool this garage down is appreciated.
Old 08-23-16, 11:26 AM
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Are the walls insulated? Is there any source of cooling into the space?
Old 08-23-16, 11:51 AM
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Insulation may help if the heat gain is from the sun, but more insulation often just holds in the heat from parking hot cars in the garage.

Often the solution is to add a thermostatically controlled vent fan with appropriately sized inlet vents for makeup air. Good sized wall fans with automatic shutters are relatively inexpensive.
Old 08-23-16, 12:58 PM
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I have a well insulated garage and it gets extremely hot in the summer. Since I don't run the garage AC very often the coolest it ever is is either the average outside temp (if the doors have not been opened) or the outside temp (if the doors have been opened). So, in the summer you start with a pretty hot baseline.

Then pull in a couple hot vehicles and shut the doors and you've soon got an oven. As a fix I've installed a large vent that I open in the summer that opens into the attic and have vents low near the floor. With the vents open there is good airflow to cool (relative) things down.

In my case the roof is 15-30 feet above the garage floor so I'm not sure my insulation is helping much in the summer. The roof is high enough that I doubt I would feel a lot of radiated heat, especially with the sheetrock acting somewhat as a barrier.

The biggest benefit of insulation for me is in winter. Even during the coldest periods it never gets below freezing and pulling a hot car in does quite a bit to warm it up.

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