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

[ovrszd]

Open studs, with no insulation.

That's your problem.

A metal sided building without insulation is a "pop can".

You didn't say what your siding is. But it doesn't matter.

Without insulation your building is only going to be comfortable when the temperature is adequate that you could work outside. What's the point in that??

Insulate the snot out of it. Then save up your money. And insulate the snot out of it again.

My shop has 12" of insulation in the roof. 8" in the walls. I'd add more if I could figure out how.

Insulation is every bit as important when it's hot outside as it is when it's cold outside.

 

[AGRIMAN]

I would put 3" of closed cell foam in the roof. It you plan to leave it exposed, I would also paint it white. This will add UV protection and brighten up your work area.

 

[CNC Dan]

Paint the roof white.

 

[brown40]

If its an unheated space the bubble foil insulation works blocking radiant heat transfer, especially with an air gap. Light, easy to handle, cuts with a knife, no fiberglass and mess, and comes in foil or white.

 

[tractchores]

I have the same issue. I need to put a fan in the upstairs space, it gets 20-30 degrees hotter than outside. Until I do that I just use a big window ac over my work area.

 

[bigdeano]

I put 8" of fiberglass insulation in the ceiling joists of my wood garage. It made a huge difference keeping it cool in the summer. The walls aren't insulated. I didn't want to go to all the work of putting plaster board on the ceiling, so I stapled heavy weight clear plastic sheet to the joists so there isn't fiberglass raining down. It's been there 15 years and still working good.

 

[AGRIMAN]

If its an unheated space the bubble foil insulation works blocking radiant heat transfer, especially with an air gap. Light, easy to handle, cuts with a knife, no fiberglass and mess, and comes in foil or white.

I have this in one of my buildings and I agree it's easy to install and does seem to work good. I was pleased with it for the first few years, but now I'm not and wouldn't recommend it.

After 5 or 6 years it started falling apart. The white backing material cracks/flakes off in little round circles (same size as the bubbles) and it looks bad. It's a never ending battle trying to keep it cleaned up.

There are several areas were it has started to pull apart and sag. I have also noticed that many of the bubbles have busted and I doubt it has much value any more.

I'm going to cut it out and replace it with foam.

 

[ray66v]

90% of the heat comes from the roof.

If you put any kind of ceiling up, with even just R19 insulation, it will make all the difference in the world.

Going further, like more insulation in the ceiling, attic fan, or insulating the walls, will all obviously help. But, a basic ceiling will give you the most bang for your buck.

My shop has only had a drywall ceiling, and with R19 in it for 5 years. It never gets hot in there anymore. And, it never gets much below freezing in the winter, even with no heat.

 

[Cord]

Insulate the walls and ceiling and install a attic fan with a thermostat. The fan does a really good job of cooling the attic which in turns lowers the temps in the building.

 

[GManBart]

I partitioned off a 24x40 section of my pole barn, so I'm dealing with a similar size area. I insulated between the trusses with 32' long rolls that my neighbor gave me, added a vapor barrier, then hung metal liner panels on the ceiling (13' 4" or so). Next step there is to use blown cellulose to get it to R40+. I insulated the partition wall with R13 and then covered it with OSB on the barn side. I insulated the exterior walls with R19, and covered that with R5 foam board between the girts for the inner liner panels, and then hung steel on the walls. I have an insulated overhead door to the outside, and I'm going to install an insulated overhead door in the partition wall soon. Even the way it is I can walk from the partitioned side to the open side and feel about a 10*F change in temperature. I'll be adding a 30K BTU Mini-split here before long so that next summer I can really work on finished the bathroom, etc and not get cooked.