In our coastal VA climate I find the benefit of insulating garage walls is that the garage stays a little warmer during our (relatively brief) winters especially if the water heater is in the garage. I don't perceive any benefit in the summer months.

Insulate the garage and do not mush down the blown in insulation at all.

Having lived in Texas, install insulation. Your garage will get hotter than hell. The heat will melt anything rubber. I would consider a radiant barrier material, too.

We just built a home in central Texas and had the three car attached garage insulated. The builder decked the space above the garage for storage. We already see the benefits in living here less than a month.

The radiant barrier is a good suggestion (in addition to insulation). Insulation is worth it if you can afford it now, if not DIY it at a later date. Do not lay anything on top of blown-in. Actually, with blown-in good bet you probably have trusses and shouldn't really be using them as attic storage anyway. You should have proper passive attic venting and shouldn't need any additional mechanically activated vent.

I don't know - insulation creates a bit of a hot box environment. Would not do in a hot environment but orientation matters.

I don't know - insulation creates a bit of a hot box environment. Would not do in a hot environment but orientation matters.

Agreed.

My husband and I built a tract house in Central Texas almost 4 years ago, and the garage's exterior wall faces north (the door faces west). We declined insulating it, since the north side is the coolest, anyway. The door itself isn't insulated, so I didn't want to trap heat in. :-/ I may have faulty logic, in which case, I'm sure someone will correct me. lol

OK I'm confused. I don't understand how insulating a garage will keep the heat out at all or make the garage cooler in the slightest?

At best I would expect it might take slightly less time to heat up during the day than an un-insulated garage. So maybe you reach 120 at 1P rather than noon? But then if insulated it's just going to trap and retain the heat that much longer in the evening/night.... Or am I missing something here?

The house attic (foam insulation in roof) will be segregated from the garage attic. Likewise the garage attic is essentially sealed from the garage space below. My thought was to introduce a modest amount of airflow from an exterior garage wall via a vent, into the garage, then another vent in the ceiling up to the attic and finally from there - soffit vents out... Might take the edge off a little in the Summer in theory...

Definitely planning on putting a few sheets of decking up there to store stuff like boxes, maybe some decorations or whatever. Given blown in is typically over the joists - it will be compressed slightly - or use something else - or simply skip the insulation altogether...

thanks

The radiant barrier sheathing one poster suggested is a good idea. I'd avoid any mechanical ventilation of the attic over the garage. Just soffit and ridge vents.

I would do it. We didn’t and I regret it. I would also add a window that opens

QUESTION: If I go w/ spray foam in roof space over garage instead of blow in over ceiling... would they typically NOT have soffit vents?

The attic space over the garage would still be segregated from the foam insulated attic space over the living space?

Drive a hot car into the insulated garage in the dead of summer and you'll understand the hot box discussion. (and the larger the motor, the more heat soak happens - park the diesel truck

in there and it's crazy hot...)

I think rigging up an exhaust fan to clear out fumes and some of the hot air after coming home in the summer might be the nicer thing. And depends on how cold things get / garage orientation....

Worse yet, drive that hot car into a garage in the late afternoon in a region where the lows are 89 and the highs are 105 in the Summer...

Perhaps the best solution in hot climates is some sort of combination of insulation and ventilation.