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Help - Garage too hot to Work In

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SomeGeoffGuy

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Joined
Mar 23, 2012
Messages
7
Location
Southeast Michigan
So I built my dream garage a couple years ago. It is 40 x 28 with three stalls and a work area on one side. About 10 feet of each side has a little storage loft with floor joists, and the center of the garage has scissor joists so I could put a 13 foot two post lift in. I really haven't been able to start any projects, though, because it is just too hot in there. Like today, it was 82 and sunny outside, but in the garage it was literally 100 degrees.

I built it with a ridge vent and soffit vents. What I think is happening though, is that since the whole inside is open, all the heat just radiates in from the hot roof, and the vents aren't really working properly because they are not isolated from the rest of the garage.

What I am thinking about doing is insulating to keep the roof cavity separate from the parking/working area. I was going to "finish" the ceilings with 3/8 MDF, and then get Ace and Sons to come out here and blow in some insulation. I included a pic of the ceiling area for reference.

Any thoughts or ideas on this plan? How much insulation do you think I need to get the roof separate from the rest of the garage? I am not interested in heating the place in the winter, I just want to keep from overheating in the summer.

Thank you.

-Geoff
 

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speedoo51

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rocky hill, ct
6" bat at the bottom of the trusses, then 1/2" sheet rock, makes insulated barrier for roof cavity...Soffet vents between every truss to let air in to flow up roof sheathing and out the Ridge and Gable vents..Will make a huge difference, even just adding the soffet vents should help.....
 
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mike93lx

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Richmond, VA
Mdf is a terrible material for that as it will absorb all of the moisture and end up moldy. Sheet rock is the right stuff.

You might also consider rolls of bubble insulation. It might help enough and would be much cheaper and easier
 
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Fixin'Stuff

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HotterNHellHouston
Bubble insulation is pretty close to R-Zero. Insulation works by having millions of tiny spaces that trap air. Bubble "insulation" has 2 spaces. Just stapling plastic sheeting to the ceiling would be nearly as effective, and a hell of a lot cheaper. :(
 
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SomeGeoffGuy

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Mar 23, 2012
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Location
Southeast Michigan
speedoo51 said:
6" bat at the bottom of the trusses, then 1/2" sheet rock, makes insulated barrier for roof cavity...Soffet vents between every truss to let air in to flow up roof sheathing and out the Ridge and Gable vents..Will make a huge difference, even just adding the soffet vents should help.....
Click to expand...

It has a fully vented soffit - plastic with with the recessed holes inside the groove. How far up do I go with the insulation, or am I just trying to make a seal against the wall. They make a 24" insulation batt, but it would have cost a small fortune to do the whole garage.

The reason I didn't consider sheet rock is that the garage has 24" joists I though it might sag. Is 1/2" thick enough so it won't close-line on me?

Thank you for the tips.

-Geoff
 
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Shiftless

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East Bay SFO
I agree with ducksface:

Install a thermostatically controlled monster exhaust fan in one or both of your gable ends and perhaps add a few large louver vents down low in a north facing wall. Relatively cooler outside air will flush out the hot air and keep you cool enough to get some work done. Then save up some $$$$ to get the place well insulated.
 
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Firebrick43

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May 12, 2015
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Location
West central Indiana
How about pole barn liner for the ceiling? It cheap, lightweight to put up, pre painted white and good light reflector.
https://www.menards.com/main/building-materials/pole-barn-post-frame-materials/steel-panels/dura-panel/p-1444448673649.htm?tpt=5_en
Cellulose is the best value for insulation and air sealing abilities. Shoot for 20-22 inches. Even though you are not heating it, the more insulation the better. 12 inches would make a huge difference however. But for a few hundred more you can future proof things for when you do decide to heat and cool things.

I would still staple up a plastic vapor barrier between the truss and ceiling. Remember you need insulation blocks and chutes to keep insulation from getting into the soffit and allow ventilation
 
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PFSard

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Sep 12, 2013
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Mesa, AZ
ducksface said:
It was 102 here today.
Interior of garage was 62 this morning at 6am and 68 today at 7pm.

Open your garage tonight at 11pm,close it at 6am, refrain from opening anything but the man door.

I am super insulated and you skipped that step initially.

Until you get it insulated open the doors and plant a fan.
Air exchange won't allow temp to rise past ambient.
Click to expand...

Wow!!! What was the low of the ambient air temperature outside that allowed your garage interior to hit 62? With these 85-90 degree lows around here, my garage won't cool down below 88 degrees.
 
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ddurrett896

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995
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VA
ducksface said:
It was 102 here today.
Interior of garage was 62 this morning at 6am and 68 today at 7pm.

Open your garage tonight at 11pm,close it at 6am, refrain from opening anything but the man door.

I am super insulated and you skipped that step initially.

Until you get it insulated open the doors and plant a fan.
Air exchange won't allow temp to rise past ambient.
Click to expand...

Mind adding what you did as far as insulation,etc? With temps like that, I don't see a need for any central air.
 
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bzinsky

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Oct 27, 2014
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5,565
I would think the first step would be a reflective paint on the roof, minimize the source of the heat before trying to get rid of it
 
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kckndrgn

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Apr 13, 2017
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Somerville, TN
I just finished a 24x48 build. I had a powered attic fan (roof mount, not gable) installed when the roofers where doing their job.
No insulation, yet.
Highs have been in low/mid 90's. The attic fan is set to kick on/off at 100*. I have not had any issues working in the garage, the attic fan does a great job of pulling the heated air out of the attic space. It's rated for 1000CFM and up to a 1600SF attic.
While my attic space does have some flooring laid down, there is plenty of airflow from the work area to the attic.
 
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soapii

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SE Michigan
PFSard said:
Wow!!! What was the low of the ambient air temperature outside that allowed your garage interior to hit 62? With these 85-90 degree lows around here, my garage won't cool down below 88 degrees.
Click to expand...

In the summer my garage operates the same way as ducksface. As long as I keep the garage doors shut most of the daytime it stays 65-68 due to the slab staying cool. My garage is insulated well (spray foam walls with batt and blown in insulation in the attic and 2" insulated doors).

--Joe
 
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yeldogt

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Jan 2, 2012
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The soffit and ridge vent is not intended to keep the whole garage ventilated -- and never would it cool it. The vents are designed for keeping he roof deck cold in the winter -- they do very little in the summer. That's why in many claimants the attic is closed or is made into a conditioned attic.

You have to insulate the space -- go from that point on what conditioning is required.


did you insulate or VB the slab?


A well insulated/ tight building with a slab that's not properly isolated from the earth can end up needing humidity control if no AC .. even with on the shoulder seasons.
 
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SomeGeoffGuy

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Mar 23, 2012
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Southeast Michigan
yeldogt said:
did you insulate or VB the slab?
Click to expand...

Thank you everyone for the tips.

The slab is not insulated but they laid down a layer of heavy plastic underneath it. It hasn't sweated on me once in four years. It is a full 6" pour and very well drained (they built up the base almost four feet). Plus the footing is monstrous - it is 42" deep and has three truck loads worth of concrete in it plus #5 re-rod.

Funny story about the foundation pour. They originally dug it out to 12" wide with a tiny back-hoe, but there was a problem with the permit, so it was almost a month before they poured it. So in that month, it eroded and eroded, getting wider and wider - almost v-shaped. They came back a month later and squared it best they could, but ended up just pouring it full. That footing is going to be on this planet longer than I am! It is 3 feet wide at the top at some points! So the floor is poured on that footing edge all the way around. With the whole thing filled with good draining fill (no clay) and crushed concrete.

-Geoff
 
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akpingel

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Huntersville NC
yeldogt said:
The soffit and ridge vent is not intended to keep the whole garage ventilated -- and never would it cool it. The vents are designed for keeping he roof deck cold in the winter -- they do very little in the summer. That's why in many claimants the attic is closed or is made into a conditioned attic.

You have to insulate the space -- go from that point on what conditioning is required.
Click to expand...

Ill save you 100 bucks and the headache of install by confirming this, and adding that a gable fan won't help. 2 weekends ago I installed one, and have noticed it only slows the rise of the temperature and really only works in the first truss area. Here is a shot from my thermal camera with the fan in action. Notice that the second and third truss bays are significantly hotter.
2017-07-17_01-24-11 by Alex Pingel, on Flickr

I did this in attempts to save a few degrees and get my shop closer to workable. Bottom line is it will be stupid hot until I get sheetrock and insulation in!
Cheers,
Alex
 
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SiGmA_X

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Portland, OR
Gable fan helped substantially in the 24x48 my friends and I rent. But only because it creates cross-flow. The ceiling is insulated with R13 in the front 3 bays, the back bay is not insulated and that area is noticeably warmer.

In the OP's case, I would not start with the gable - I would start with insulation and go from there. A ceiling and blow in or batts would probably be the best to start.
 
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matt_i

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SE Michigan
I think you should investigate whether the soffit vents are sufficient to feed the ridge vent. Ideally they should have equal cross sectional areas. I purposefully oversized the soffit vents in my shop and it seems to be working reasonably well. Reasonable temp in the attic when its bright and sunny outdoors.

I also have a 72" ceiling fan in the work area blowing when I work. It seems to help at least distribute the heat so its not concentrated.
 
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akpingel

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sourdough

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Pe Ell, WA
soapii said:
In the summer my garage operates the same way as ducksface. As long as I keep the garage doors shut most of the daytime it stays 65-68 due to the slab staying cool. My garage is insulated well (spray foam walls with batt and blown in insulation in the attic and 2" insulated doors).

--Joe
Click to expand...

I have a 40' x 32' x 10' garage with a 6" slab, 2" x 6" R-21 walls, R-30 ceiling, no hvac or fans. I keep my 2" insulated garage doors shut nearly all of the time unless we are working the property or mowing grass. Year round, with the temp in winter (10*) it never goes below 40* and during the hottest summer months (100*) it never goes above 74*. Before we had A/C, when it was very warm outside I would sleep comfortably in a light sleeping bag on an air mattress on the garage slab as opposed to sleeping in the house at night.

The 6" slab is a huge heat sink, and I am grateful for it.

Jim
 
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