How to cool a hot texas garage?

[stonewall]

New house and detached garage built last year. South central Tx. Both are spray foamed walls and roof deck

Fwiw- I wish I could have seen this thread before we built

Spray foam insulation

Does anyone have it in their attic? I've been told it's great on the electric bill. Also been told it causes mold and moisture problems. One ac guy told me not to use it because the ac unit wouldn't run efficiently. Another told me he's never had a problem. I'm not sure which way to go. Thanks

rokslide.com

The garage is insanely hot. It keeps the daytime heat in and is scorching even at sun up

My parents detached garage was built late 80s early 90s range. Bat insulation in walls and ceiling. Soffit vents and fans in gable vents. Don’t remember if there’s a ridge vent. I can feel the heat being blown out of the gables when standing outside. But in their garage the temp is always noticeably more pleasant (much cooler)

I asked the builder to insulate our garage thinking I’d have same experience my parents have had. And since the house was spray foamed we spray foamed the garage. And in my little mind I thought the garage attic would then not be so hot for storing things. Way way wrong

Is there anything I can do now to keep it from being so hot? Should I insulate the ceiling and attempt to vent the attic somehow? Or will that cause moisture problems in the attic?

 

[AndrewD]

From what I know, which ain't much, spray foam sprayed on the bottom of the roof deck (ceiling) of metal unvented roof structures, is ideal for preventing condensation and mold, which you would have with fiberglass insulation since foam bonds directly to the roof deck and fiberglass settles and leaves lots of airgaps for temp differentials to occur.

Vented DOES not mean that the ridge cap allows the small amount of air between the roof deck (plywood or OSB usually, what the metal roof rests on) and the metal roof itself (the air inside the raised ribs of the roof) to vent out the cap. That is great, but what a real vented roof system does is allows air to flow up through the eaves/soffits and into the area below the roof deck, and escape through the cap. This requires that there is a gap between the insulation and the bottom of the roof deck, so that the air above the insulation is temperature equalized with the air above the roof (basically, it allows outside air to flow underneath the roof deck). This not only keeps the roof cooler, but it also stops condensation.

So, does your garage have a true vented roof, or was it unvented? If it was a simple, unvented roof, then spray foam was absolutely the right choice because it is best way to prevent condensation. But you don't get the cooling you get with a vented roof. If this is the case, then you need to look at cooling the garage space in other ways, like putting an exhaust fan at one gable end and a passive vent at the opposite gable, so the hot air in the garage space that rises up towards the ceiling gets vented out with fresh air. Pretty doable DIY project if you're handy.

Edit: Just reread your post and saw that the garage has an attic above it. I think your first step is to vent that attic, prbably with the exhaust fan at one end and passive vent at the other, like I described above.

 

[Rich M]

You can install a solar powered vent fan. Get the hot air out. Insulating the attic floor might help keep as much heat from toasting the main building part of the garage.

Not sure if your garage is in full sun or not - I know that a building in FL sun, without AC will heat up pretty quick.

 

[Jstumbaugh]

Put in a minisplit and be done.

 

[Wireman07]

Put in a minisplit and be done.

This 100%

 

[Mike Islander]

Put in a minisplit and be done.

Plus 1. I have a 30 x 20 insulated "chill room" for storing a product we manufacture. 1 ductless AC keeps it around 60-65 degrees. It's built inside my 100 - 105 degree warehouse.

If you don't want to pay for cooling your insulation is working against you. You need venting, and lots of it. You have to literally move air through the space to cool it to ambient temp. Impossible to get it below ambient, except for mornings after the slab has cooled overnight. Pure physics.

 

[stonewall]

Thanks for the replies.

Garage is brick. Roof is asphalt shingles. Full sun

Mini split has been a thought I had as well. It does seem a little strange to spend that extra energy on just a garage but it may not be so bad. I’ve seen ads for DIYing thoughs - has anyone done that or should I just have a pro do it?

 

[Dos Perros]

You ever considered putting solar on the roof? Take some of that heat and make electricity. I don't know the economics of it but my buddy in the Hill Country does that. Has a Tesla battery station. Sells surplus to the grid.

 

[Wrench]

Attic fans on thermostats and a mini....in that order.

You insulated to reduce the conductivity of your roof.....but it's texas and hot. You will have heat build. The fans will draw out the hottest air up high. Remember that the fans can only move air that can be replaced by new air...so the building has to be vented enough to allow the fans to work.

 

[CRJR45]

Thanks for the replies.

Garage is brick. Roof is asphalt shingles. Full sun

Mini split has been a thought I had as well. It does seem a little strange to spend that extra energy on just a garage but it may not be so bad. I’ve seen ads for DIYing thoughs - has anyone done that or should I just have a pro do it?

I installed a Mini Split , it's a piece of cake . Just get the purge kit to purge the lines before you open the freon reservoir .

 

[Theringworm]

You created a sealed envelope by foaming the roof deck down the walls to the foundation, smart choice. Without some sort of coolant/refrigerant inside, why would it stay cool. Instal a couple of mini splits and be done with it. The idea/goal with spray foam is to have a conditioned space all under one roof just like inside your home. To add in ridge vents and soffits in this setup would be wasting the expense of what you did with the foam. If super concerned about moisture also install an HRV to move fresh filtered dehumidified air in and out of the building. Obviously this will be less effective compared to your home given the garage doors and large shifts of unfiltered dehumidified air, but it’s a relatively cheap solution.

 

[Braaap]

I solved that problem by moving out of Texas .

 

[dtrkyman]

Insulate the door as well if you haven't, vent fan would be a great idea, I would imagine a mini split would run all day without some type of venting to get the heat out.