Hi all, I'm looking for potential solutions to a problem at a client's house.  The south facing 2 car garage gets extremely warm in the summer months.  The heat coming from the attic thru the uninsulated garage ceiling is the primary culprit.   Any advice on how we can lower the temperature in the garage is much appreciated.

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Easy... insulate the attic ceiling. I'm not sure how much good it would do to air seal a garage ceiling, especially if walls are typical uninsulated but it would be relatively inexpensive to air seal the ceiling before insulation goes in. Also, if the door(s) face south and are not already insulated, I would consider replacing with insulated door(s), or surface-attach some foil-faced polyiso to the back of the door. Pretty? No.

There are only two methods - block the heat before it gets in & exhaust what gets in

Blocking - numerous methods like David pointed out - you can also shade it, use cool roof coatings, go with a hot roof....

With that, your garage can still get hot from things beyond what manages to get past the insulation, from cars, to people, to machinery, to... so that leaves 

Exhaust it - want to spend a ton, put a AC unit in, if not consider a fan to pull the air out & pull "fresh" in which are readily available, check out for garage exhaust kits with some even being temperature controlled

Just curious: why do you care if the garage gets hot? Do the folks spend a  lot of time in there?

Also, do you know if it is affecting indoor thermal conditions (including radiant temperatures) and energy use? I have been wondering how much my  hot garage affects the adjoining rooms. I have done some insulating & air sealing, added a roof turbine vent, and shaded a small W facing window.

BTW, detached garages are recommended for reducing pollutant intrusion into homes, but it might be hard to retrofit in your case and mine.

TIA, Tom

Is A Garage Air Conditioner Worth It?


Obviously, the answer to this question will vary from garage to garage, and person to person. For many people, it may simply not be worth the time, money and effort to install an air conditioner in the garage. For others, this may be a life-saver that makes your day-to-day more comfortable.

No matter what scenario you find yourself in, ask yourself these three questions when you are trying to make your decision on whether it’s worth it for you:

How hot does it get where you live?
How many hours do you plan on spending in the garage each day?
How many months will you have to deal with the warm weather?

If the temperature outside often gets extreme in your area and you plan on spending a lot of time in your garage, it may be worth the effort to install some type of cooling device in your garage. If you don’t spend much time out there, it may be easier to just get a simple fan to keep the air circulating around you.

Mini-Split Air Conditioners

A mini-split air conditioner is another cooling option worth considering. As the name suggests, this type of air conditioner is split between the inside and outside.

They are appealing as a garage air conditioner because they don’t require ducts and are known to be extremely energy efficient. They are also mounted high up on the wall, allowing your floor space to be preserved.

Is the roof ventilated, if not a couple vents would help get rid of a lot of heat. If the lower portion of the garage is fairly tight some make up air would also help.

A two garage can be 400 square feet or more, so if its not insulated, it should be. If the roof over the garage is lower pitch, then the residence time of the heat over it will be longer, so we install a lot of solar attic fans down here to keep the hot attic air exchanging faster. I am in climate zone 2, Houston Texas.

Another culprit is the garage door. We cut radiant barrier to fit each panel on the door. Clean the metal support, top and bottom, of each panel, then attach the barrier. I tell you, THIS WORKS AMAZING! My customers love it. You can also, lay the barrier down over the garage attic, if the home owner wants to go that far.

My personal garage had the same problem.  No drywall ceiling in garage.  So I put a ventilation turbine in the roof deck.

Hot air rises, as we all know, so remove it up high and bring in cooler outside air from lower.   

Take a page from the Code.   Garage requires 100CFM ventilation per car.  So install that much,   I would think about half ventilating the attic 24/7, and half on a timer in the garage itself.  Read the iCode, not what is adopted in your area.  You may want to recommend a trip on for 5 minutes when the garage door opens to remove the CO.

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