cooling a detached garage with limited ventilation

[poundkey]

Hey y'all,

I have a single-car detached garage that I'd like to keep cooler during the southern California summers. Its metal door faces south, it shares walls with other garages on each side (there are four single-car garages under the same roof), and there are only two vents on the north-facing wall, both about two feet from the floor. The roof has no insulation. It regularly gets up to 110F inside during the summer. I only use the garage for storing a car and some non-important belongings, so it doesn't need to be cool enough for me to work in.

Assuming that the HOA won't allow me to install any additional vents, what are my best/easiest options to keep it from getting so hot?

I understand that the roof is the best place to start, but I've thought about tackling the door first since it gets too hot to touch during some summer days. If I were to install Reflectix radiant barrier (with the sealed air gap, per recommendations), do y'all think that would do much given the lack of ventilation? Do y'all think that the Reflectix would prevent effective heat dissipation during the summer nights?

Thanks for your help!

 

[u2slow]

AC normally works best when isolated and insulated from the outside. Roof/atic should vent itself separate from the interior. Work on that, and probably a mini-split unit so you don't need ducting. Will need a condensate drain line for sure.

 

[nadogail]

Welcome to the forum from the shore of San Diego Bay.

Try reducing the heat gain by adding insulation to the door, maybe you could add a reflective coating to the roof.

Without adding additional vents, can you have a thermostatically controlled exhaust fan?

Can you add another cover over the roof, maybe with 3" of open space and lots of air circulation to keep the sun from beating directly on the roof? Think of a Ready Service Box or Pyrotechnics Locker such as on a Navy Ship.

 

[poundkey]

The HOA won't allow any roof modifications.

However, there is power in the garage, so your idea of a thermostatically controlled fan is great!

Thanks!

 

[Shiftless]

The bare concrete floor will absorb some heat but is obviously overwhelmed by the complete lack of insulation.
Since you can’t modify the roof, it seems to me that your only option is to build walls inside the existing walls and insulate the heck out of them. I think foam has the highest R value per inch.
How much space can you afford to give up to add insulation to the walls and to the ceiling?

The fan is a good idea but realize that the fan can’t get the temperature below that of the outdoors.

Will the HOA permit you to install a mini split AC in your garage? Where would you put the outside heat exchanger?

 

[PoorUB]

Is it a wood truss frame roof? If it is, then sheetrock the lower cord of the trusses and insulate the top of the sheetrock. Insulating the walls will help as will the door. If you have a couple vents you could put a fan on a timer and run it from say midnight to 6 AM.

 

[poundkey]

PoorUB: Yes, it is a wood truss frame roof. I had considered adding a "ceiling" to the lower cord of the trusses - and I still might do that. And the fan on a timer is a great suggestion as well. Thanks!

Shiftless: The AC isn't an option, unfortunately. Also, my main goal is to keep it from getting above about 90F, though this is somewhat arbitrary. I'm not storing anything super temperature-sensitive, but I figure that anything I can do to minimize the heat absorption/retention will help.

 

[PoorUB]

If you have a couple vents available, actually you just need an intake as you could exhaust through the sheetrock ceiling you may be putting in, but there are two ducted portable air conditioners that will run on a 120 volt 20 amp circuit. After properly insulating the space it would do well, but probably over kill for your intentions.

https://www.homedepot.com/b/Heating-Venting-Cooling-Air-Conditioners-Portable-Air-Conditioners/Dual-Hose/N-5yc1vZc4m4Z1z17ztx?storeSelection=