Ceiling vs Wall vs No Insulation Priority Question

[treasureman]

I have been working on completing my garage projects so I can have it be cool in our high heat environment . In Arizona, AC is the big issue, as we are in the desert and heat is seldom used. When I started the project, I replaced the metal garage doors with R20 doors. My garage is 18 by 31 feet in size. Purchased my Mini Split (Mr Cool 3rd Gen 18k BTU DIY 20 Seer). Have yet to turn it on.

I had planned on immediately insulating the rest of the garage. These days I am holding off on some expenses until I know when I can be back to work. I was planning on professional foam insulation in the walls and blow in insulation in the attic. Trying to finish this project, for now, at the lowest cost. We are one month away from the high heats. Here is my question:

Do no insulation now and wait until next year? I had estimated $20 a month for electric operating cost based on insulation installed.


If I have to pick, would you do attic insulation before wall insulation? My long 30 foot wall with no insulation is mostly in the shade during the day. Wall is constructed of Stucco over styrofoam 1". No insulation between the studs.

Any advice appreciated. Thanks!!

 

[burleyfarm]

My $.02. I would definitely insulate the ceiling first otherwise it’s going to feel like an oven in the garage. Is it already dry walled? Blowing it goes fast. Make sure you have the proper venting for your soffits.
What size wall studs do you have? The R-value of the foam will determine how much you will eventually need in the walls. If the existing foam has 5+ R-Value fiberglass batts may be enough.

What ever you do spend the time to seal all air gap locations. Seams, plug, light and switch locations, wire penetrations etc.

Good luck.


Dave

 

[harley jim]

I would do the ceiling first, you will get way more heat build up in the attic than you will get from the walls.

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[ripperd]

ceiling first, 100%.

Also, if you have 2x6 walls then IMHO batt insulation will be perfectly sufficient and significantly cheaper than foaming. Unless you really want the tightness that foam provides.

 

[Toomanytools?]

Yes ceiling first, the Stucco wall will give some R value, if there is a South facing wall that would be the next choice to keep heat down.

 

[jimxwill]

The real question is how well the building is air sealed. No sense running the AC when it's just going to leak outside

 

[ddawg16]

Yes...ceiling...

But go ahead and do batts in the walls.

My old garage was not insulated nor drywalled.

New one is NOT insulated...but I have drywall. It does a surprising good job of keeping it cooler and warmer.

Insulation will just make it much better.....and cut down on the noise.

 

[ducksface]

I owned two houses in Havasu, side by side, for fifteen years. Six or eight gj members have been there.
Both houses had so much blown in ceiling insulation you had to tunnel through it.
6 inch walls well insulated, both had carpeted floors and insulated garage and man doors. One small window, covered.

The Mini split isn't even going to start to be of value to you.
Unless you're running it 24 hours a day you're going to have to plan HOURS in advance to work out there and then it's gonna be 90+ inside.

I had a six ton on one 20x24 garage and a four ton on the other. Both roof mount, both ducted as central air with a pick up and six discharge. They took half an hour to drop it 20 degrees.

They worked well until you opened the garage door and then you got to start all over.

If you don't have the whole garage insulated or working at midnight till 5am in there, when it will still be 90°, you're wasting your time.

You've neglected to give people a background on lake Havasu city.
We had a swimming pool cooling tower. Shade Temps of 123° multiple days in a row, pavement Temps in the 160 range reflective wall temps just as high, 16,000 gallon in ground pools hitting 103° for a month or better all at 2 to 6% humidity. Midnight at 101°

'Lake Havasu City holds the all-time record high temperature in Arizona history with 128 °F recorded on June 29, 1994. This temperature is also the highest for a town or city in the Western Hemisphere.'
Havasu is often the hottest city spot in North America. Often often.

https://www.google.com/amp/s/amp.azcentral.com/amp/507998002
The article has a few wrongs or lies, your choice, in it. Death valley prides itself on hot, Havasu measures their Temps five feet off the ground out by the airport far from pavement and town. Havasu can be and has been the hottest place on earth and is often the hottest municipality on earth. It's not exactly something you advertise when you're a tourist town with not a single other purpose for being there.

Not mentioned anywhere you'll easily find is it is also the second windiest lake in the country topped only by Lake of the Ozarks or the lake next to LOTA who's name ezcapes me right now.

(I used my heater often. Your uninsulated garage will be below 40 inside on winter mornings.)

Punchline:
Any advice given to this op needs to be at least doubled just for the numerical temperature differences, and times four due to the exponential nature of temperature and heat soak.
You should alway always always consider the location when giving or accepting advice.
Local is always the most valuable.

 

[Kaizen]

Damn swimming pools over 100 degrees?!?!
In the short term till money flows I’d put up a reflective one or two inch panels on the ceiling to reflect some heat up. Depending if you can sacrifice height you can later come back and add furring strips as support for blown in and the ceiling material. I hate doing things twice so I try and install logical steps to get final product eventually.
If possible I’d add trellises or something on the outside walls to make some shade on the walls.
Imo if you have it installed and it gets it from 110 down to 80 it’s worth it. Wouldn’t run 24/7 though.


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[Nivekdodge]

Foam- first, last, always. I'm so impressed. its expensive but worth it.