Garage Insulation

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Forum topic by LeeG posted 03-03-2010 09:16 PM 4156 views 0 times favorited 9 replies Add to Favorites Watch
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40 posts in 3049 days

03-03-2010 09:16 PM

Topic tags/keywords: question

My garage is my workshop, and I want to be able to work out there this summer, so I will need to insulate and cool it. I live in the Phoenix area, so heating is seldom an issue, but with summer temperatures reaching as much as 120, cooling is going to be important.

I have a south facing garage door, so the hardest to insulate wall is the one that will need it most. I am considering just having insulation blown in for the walls and ceiling, and some sort of radiant barrier + as thick of foam insulation as I can fit for the door. For the AC, probably something like a 15K btu PTAC unit (I don’t have any real room on the side of the garage as the house is very near the property line).

If anyone has any suggestions or tips, I’d love to hear them.


-- Lee in Phoenix

9 replies so far

View BTKS's profile


1986 posts in 3492 days

#1 posted 03-04-2010 06:40 AM

Sounds like you need some serious R value per inch. Look into sprayed in expandable foam. Closed cell, open cell and hybrid. The close cell had the best heat transfer rate but is the most expensive. The closed, I’ve been told, will echo like a tin shed because it’s so hard. I just had hybrid installed in my in-laws house and it is great. The snow on the sills melted before the roof line and that’s with a master bedroom in the original attic space. Hybrid and Closed cell will create it’s own vapor barrier but may cause a problem if you need makeup air for anything like vented dust collection. Just a point to consider.
If you do use a vapor barrier it always goes to the hot side. This prevents condensation being trapped in the wall when it reaches the dew point somewhere in the insulation layer. I reside in the mid west and we have conversion every season, hot side just became cold side. I’ve had condensation form on the wall behind insulation resulting in mold, another advantage of foam, no food for the mold. The foam is expensive but really good. Hope this helps, BTKS
OH YEA, Welcome to LJ’s.

-- "Man's ingenuity has outrun his intelligence" (Joseph Wood Krutch)

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Steve Peterson

377 posts in 3110 days

#2 posted 03-04-2010 07:03 PM

I put 1.5” thick styrofoam panels in my south facing garage door. I got 4×8 sheets from the big box store. They also have kits of pre-cut panels, but they were not the right size for my door. I cut them a little wide and used a putty knife to compress them slightly so they slide under the lip on the door. The springs needed to be adjusted slightly even with the small additional weight of the styrofoam. I think the R-value is around 6 for a 1.5” thickness. You might be able to glue an additional 1.5” thickness to double the R-value. Of course, use a glue made for styrofoam and test it on scraps to see how it holds.

I am near Sacramento, CA, so it is not quite as extreme as Phoenix. I use a 14K BTU window mounted air conditioner for cooling my single stall workshop and I can cool the room to around 80 degrees on the medium setting.

-- Steve

View energy's profile


1 post in 3027 days

#3 posted 03-11-2010 07:51 AM

It sounds like you are on the right track. I certainly would bring your walls up to the highest level of fiberglass insulation you can fit in. If you don’t mind spending more money, spray foam is amazing stuff. Certainly in Phoenix, add a radiant barrier in the ceiling area. You can insulate your garage door with foil insulation which will be helpful. Another thing that crosses my mind is to control the amount of solar heat gain during the day. I don’t know what you have for windows but I would create some type of screen. Use your left over foil insulation. This can dramatically help in the daytime when the sun is at its hottest, just like shade or a car sun visor.

-- Radiant Barrier,

View ND2ELK's profile


13495 posts in 3802 days

#4 posted 03-11-2010 12:23 PM

I blew insulation in my walls and ceiling. I bought the best insulated garage door I could find. It can be below zero or 90 degrees above and it does not take very long to heat or cool it. I use a widow AC and it has no problem cooling a 14 X21 shop. Be sure and put a furnace filter in front of the air intake. If you look at my workshop pictures you can see how I hold it on. Thanks for asking.

God Bless

-- Mc Bridge Cabinets, Iowa

View NH_Hermit's profile


394 posts in 3124 days

#5 posted 03-11-2010 02:33 PM

Try this Energy Department web link:

Let us know what you decided on.


-- John from Hampstead

View Dark_Lightning's profile


3165 posts in 3137 days

#6 posted 03-11-2010 03:03 PM

If you have a way to shade your door, that helps, even if it’s a couple of movable plant stands. Just roll them in front of the door when it’s closed. I put radiant barrier insulation in my garage ceiling. My door is also south-facing, in sunny Southern California, where August of ‘08 it was 107 in the shade. That radiant barrier worked well. Just be sure to vent the hot air above it out. Also, my door has the factory-supplied foam insulation.

-- Random Orbital Nailer

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4424 posts in 3770 days

#7 posted 03-11-2010 04:52 PM

Lee – I would hit up Mr. Spagnuolo on this site aka the wood whisperer. He is also in the phoenix area and I know that in one of his videos, he showed what he had done to insulate the garage—> shop in their new home… So this is a bridge someone locally crossed and probably still has phone numbers of contractors that were good, or perhaps not so good.

One question is will you need to put a car in and out, or will it be tools only? If it will be strictly a shop, you can insulate the door better. In my shop, which I did not put in a electric door opener, because I would keep hitting it with lumber, and hung a dust collector in that place instead. Very convenient ceiling 110 plug right where it is needed.

-- “The two most important days in your life are the day you are born and the day you find out why.” Mark Twain

View Dark_Lightning's profile


3165 posts in 3137 days

#8 posted 03-12-2010 03:29 AM

Dave, I’d give a lot to not have an automatic door opener. We don’t park cars in there, it’s storage and workshop only. That motor and track seriously limit my shop. Guess I’ll broach that subject with the wife. It’s an idea whose time has come for me! It would still have to open, but that elimination would free p some good space.

-- Random Orbital Nailer

View dmorrison's profile


151 posts in 3290 days

#9 posted 03-12-2010 10:22 AM

Facing this same subject. I live in the DFW area and it gets hot. Not as hot as you do but then again hot.
What I have learned.
This is the insulation I am considering for my garage doors.

The R value is 4.5. BUT, and a big but to me, was not worrying about the foam getting wet in a thunderstorm.

Other considerations shown here.

The best R value is the bat insulation. But if it gets wet the insulation factor is destroyed. You don’t worry about this with the foam panels.

You could buy new insulated doors but that money might be better spent on tools, at least that’s how I feel.

If the walls and ceiling are not insulated blown in insulation is fast and relatively easy. How tall are your garage walls. Do the studs have fireblocks in them. If so 2 holes will have to be drilled in each section for insulation. Etc. Etc.

Now the Ac unit. I have a 18,500BTU window unit that I bought for my other house, a 2 car garage. It was adequate for my setup. That garage was a 2 car, uninsulated doors, 2 uninsulated wall, south facing, brick veneer house. The 18,500 BTU did OK, not great but OK.
The same unit in my 3 car garage is again OK but ceiling is insulated except for the outer 10 feet A finished room over the garage.
Walls are not insulated and the garage faces east. Also very large trees over and in the western sky. So the 18,500 BTU is fine.
Adding the garage door insulation and insulating the outer 10 feet of the ceiling along with garage door side, top and bottom seals should make it comfortable.


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