New garage, but it's too hot to work in it.

[PutnamVictor]

When it's 80 degrees outside, its 90+ inside my garage, with the doors open. The temperature on the celling is 125+. What is the best method of lowering the inside temperature?

Insulate the trusses/celling.
Insulate the walls.
Gable vent with or without fan
Cupola with or without fan

Garage specs:
30'x24'
2' high blocks wall and a 10 2"x4" wall on top of that, total 12'
6/12 scissor truss roof
Full soffits and a full ridge vent
Concrete slab floor
2 - 8'x9' insulated garage doors (south facing)
1 - 34" back door
Open studs, with no insulation
The building faces south with only the one tree on the west side.

 

[N2DFire]

I would insulate the under side of the roofing / trusses and install a Gable vent w/ a fan (opposite the doors if possible)

My "logic"

Ceiling / Truss / Roof Insulation:
With only one tree to provide any shade, then the roof surface is going to be the one "side" of your cube that gets the most sun light - from sun up to sun set. Therefore it will be the side that gets hottest and stays hot thus radiating heat down into your work space.

Gable Vent / Fan
As we all know, moving air feels cooler so the fan part is a must.
I chose gable over cupola by making the assumption that your garage doors are parallel w/ the trusses and thus you could maximize the air flow in the doors, across the upper ceiling area and pull; the hottest air out by venting opposite the doors instead of mid span with a cupola.

I'm not a building expert, just my uneducated thoughts.

Good Luck.

 

[bigtiller]

Your soffit and ridge vents will be adequate for ventilation. You just need to hang a ceiling and blow in some fiberglass insulation for an R42 rating or higher.

 

[s219]

What part of the country?

At my old house, the attached garage was insanely hot in summer. I replaced the garage door with an insulated one, and added insulation on all the 2x4 walls (ceiling was joists with drywall, bonus room above, conditioned space). That made a real noticeable difference -- went from stifling/unbearable to tolerable.

In my new house, the attached garage is insulated well (2x6 walls), and I also have an AC/heat unit that I fire up if I am doing any sort of detailed work for a period of time. But even without the AC, it stays comfortable/tolerable in that area and slightly cooler than the outdoors in summer.

Neither of the garages has ventilation, so based on that experience, I'd say insulation alone can make a difference.

I also have a pole barn at my new house. Wood board/batten siding (with house wrap underneath) and asphalt roof. No insulation, but it has five small windows that I leave open all summer, as well as eave venting and ridge venting. It never really gets hot in there. So based on that, I'd say good ventilation alone makes a difference.

I suspect in your case, the soffit/ridge venting is only enough to minimally vent the underside of the roof, and is not adequate to handle the heat in the volume of the building or to vent a working/living space below (roof venting is really just meant to prevent moisture issues and keep the roof from baking, and not intended to vent the structure). So you could try increasing ventilation somehow to circulate cooler air through the space. To me, if it's getting hotter than outside, that means poor ventilation. But I'd also suggest insulation, since the heat is obviously getting in through the walls in the first place. Which to start with, hard to say. Maybe consider the material costs and labor for each, and decide what makes more sense. If time/cost/labor isn't an issue, I'd insulate and ventilate.

 

[aeblank]

I'm a big fan (pun intended) of whole house fans.
3500-ish CFM sucking from the house/garage space into the attic. It does 2 things. 1) pulls in cool air from outside (run it in the evening/night) and 2) pushes the hot air from the attic OUT.

I think I'm going to end up putting one in my garage (over 1700 sq.ft.). If I can do math, that's fresh air everywhere every 5 minutes. Even in hot weather, the movement is nice.

Or throw in a mini-split. Even awesomer.

Of course, insulate first, no matter which of these.

 

[Jim Timber]

I have a whole house fan that's latched via relay to my power attic vent. When the whole house fan is turned on, it turns on the attic vent to pull everything up and out of the building. This system works remarkably well, except when the humidity is too high to matter. For days that the outside air isn't any better, there's a 240v A/C unit in the wall! I bought that thing in August at Lowe's on clearance for $350 and I can't believe I didn't make getting it a priority when budgeting the build. It's 27,500 BTU's and handles the shop (24x35x11) with ease.

As others have stated, you need to close in your ceiling to keep the radiant heated air from the roof out of the working area. Insulating the walls/ceiling will help with heat loss/gain to the outside, but mainly you want to keep the airspace isolated. Leaks are your enemy here since you're not talking about keeping it warm/cool year round. I went nuts with insulation on my shop because our heating season is often 6+ months, and I keep the building at 55F or higher year round for rust and freeze prevention (I have water in two machines cooling systems). If you're just looking to keep it warm/cool while you're out there, you could get away with plastic sheet on the ceiling and call it a day.

 

[PutnamVictor]

s219, I'm in New York. I don't mind the cold, it's just the heat that is in issue.

aeblank, I put in split system in my house, and yes it does rock! It's a bit more then I want to spend for a garage.


Sounds like Insulation is key. I kind of thought so too, but did not want to change the look of the open studs.

 

[sixdogs]

You should insulate it but you don't have to. You'll still need a big fan and a door. Get the fan at Sam's Club and you probably already have a door. It solved most of my problems. New York state is probably hot just a few days a year.

 

[RalphVa]

I'd put radiant barrier up against the rafters. Then insulate the ceiling. Been there. Done that.

Ralph

 

[George2615]

In the front part of my garage (24 x 24 x 14) the side walls are insulated (3 1/2") and sheet rocked. The ceiling just has black tarp stapled up to the rafters, no insulation. That section of the garage stays about 8-10 degrees cooler than outside. Attached to the back of the 24x24 garage is an 18 x 32 x 10 garage. The 18x32 is insulated with 6" insulation in the side walls and ceiling. Then the walls were covered with 1/2" wafer board. That section stays about 10-15 degrees cooler. That is only when the doors stay closed. I also have a large window A/C unit in the side wall of each garage if needed. With both A/Cs on full blast I can keep the garages at least 18-20 degrees cooler than outside with the doors closed. Both overhead doors are insulated doors.

A gable exhaust fan will help a lot removing the heat up top.
Insulate your walls and ceiling then cover with wafer board or plywood. (sheet rock damages too easily in a garage). One day I'm going to replace my sheet rock with board.
Add A/C units in the wall. I just came in from the garage, no A/C is on, 86 degrees outside and 74 in the garage. I'm sure if I cranked the A/C's on I could have pulled it down into the 60's. Adding A/C wasn't required but I spend a lot of time in my garage and just want to work in comfort on those 80 plus degree days.