Shop insulation /cooling advice

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Forum topic by Vrtigo1 posted 06-22-2011 09:08 PM 2011 views 2 times favorited 17 replies Add to Favorites Watch
View Vrtigo1's profile


434 posts in 3019 days

06-22-2011 09:08 PM

I posted a thread about this last year and never ended up doing anything about, but it is getting to the time of year here in Florida where it’s very unpleasant to be in my garage for longer than about 5 minutes due to the heat.

So for this post, I have two main questions.

First question is regarding insulation. My garage is approx 24×24 with 9’ ceilings, and is uninsulated. My garage door is just the sheet metal type. I’ve seen that Lowe’s sells a garage door insulation kit which looks like it consists of the foil backed foam insulation panels, and I’m planning on either using that or buying insulation panels and cutting them to size if the kit doesn’t fit.

The layout of my garage is shown below:

As you can see, the garage door faces east, so it gets sun in the morning. This isn’t a huge deal, because I’m usually out there in the evenings, when there is minimal sun on that side of the house.

The north (right) wall is cement block.

The south (left) wall partially adjoins the inside of my house, and that section of the wall is insulated, the rest of the wall adjoins a covered entryway that leads to my front door. That is just a wood frame wall with drywall on it that is uninsulated.

The west (top) wall adjoins the inside of my house and is insulated.

The attic above the garage is uninsulated. There is tons of space up there, but unfortunately I nailed down a pressboard floor shortly after moving in, so I’m thinking I’ll have to take at least some of that up to insulate it.

So in summary, I think what I need to do is add insulation to the south wall, ceiling/attic and garage door.

Now as far as what type of insulation to use, I’m not sure. Home Depot will rent you the machine to do “blow in” insulation for free if you buy the insulation from them. That seems like the only option for the walls, as they are already drywalled. As far as the attic floor, blow in insulation would be easier, but if roll insulation will be a better solution then I can sweat through doing that.

The blow in insulation that I’ve seen on HD’s website has a pretty low R-value, i.e. 4 or so. That doesn’t seem like it’d really even be worth doing. From what I’ve seen other people do in their shops, I’d want something like R-19, right?

Now the second question regarding air conditioning. Once I get the insulation squared away, I’m considering adding an A/C to keep the shop comfortable. I have no windows, so a window unit is out. I currently have a portable A/C unit which I think is 12,000 BTUs. It’s the single hose type, and it is vented out a dryer vent in the south wall.

I’ve done some research and a mini split seems like the way to go. For my second part of the question, I would be interested in hearing from people that actually have one. I’ve seen prices ranging from about $800 all the way up to several thousand dollars. What do you have, what did it cost, how much space are you cooling, insulated/uninsulated, did you install it yourself, and are you happy with it?

I’m trying to gauge what size I need, how hard installation is, and whether or not I should trust one of the bargain priced units that can be bought online or if I really need to make the 3-4 thousand dollar investment of having a local professional do it for me.

Thanks for any and all advice!

17 replies so far

View Manitario's profile


2630 posts in 2911 days

#1 posted 06-22-2011 09:34 PM

I’m up in Canada, so insulating from the heat is not too much of an issue; but I do have a lot of experience with insulating for the winter… The “best” way you’ll insulate the garage is to take the drywall off your south wall and use the fiberglass bats, or the styrofoam board in the walls. Removing the drywall will then also let you vapour barrier it. As for the garage door, personally, I’ve found the garage door kits useless; I’d buy styrofoam board and construction-glue it to the door, and then add the silver foam foil to the joints, with enought slack that you can open the door. For the cement block wall; it acts as a heat sink, ie. it will absorb the heat during the day and then radiate it into the garage at night. What you want, is to take advantage of this to help cool your garage. The best way to do this is to insulate it from the outside; this will keep it from absorbing too much heat in the day, and overall, keep the garage cooler than if you were to insulate that wall from the inside. The attic; blown in fiberglass works fine; you can go to R20 or R40.

As for the mini-split; honestly, unless you are going to heat the garage in the winter, why not just use a dedicated cooling unit?

-- Sometimes the creative process requires foul language. -- Charles Neil

View Bertha's profile


13529 posts in 2721 days

#2 posted 06-22-2011 09:42 PM

I started a thread about attic/shop insulation etc. There were some helpful responses. Good luck!

-- My dad and I built a 65 chev pick up.I killed trannys in that thing for some reason-Hog

View Vrtigo1's profile


434 posts in 3019 days

#3 posted 06-22-2011 10:11 PM

Manitario, lots of good info there, thanks. Regarding your comment about a dedicated cooling unit, I’m not sure that I follow you. Are you saying there is something other than a mini-split that is similar in form factor but that doesn’t have built-in heat? If so, could you please point me in the right direction?

View Grandpa's profile


3259 posts in 2703 days

#4 posted 06-23-2011 05:27 AM

I think Manitario is trying to tell you to go to the store and buy a window unit type air conditioner. Forget the heat part so there is no split unit. Do you really need to heat in Florida in the winter? We are running about 108 to 109 degrees in SW Oklahoma. Keep the heat out. Put in all the insulation you can get in there without compressing it. You have a lot of humidity to deal with so the A/C unit will help a lot there. Order new filters in the begining so you can was the old ones and have spares to put in while the washed one dries. Here that filter would dry in about 5 minutes.
You will need to remove the drywall for best insulating results. Blown is not the same as you have read. Might be a good time to upgrade the wiring now that you have used the area for awhile. You have an idea where you need electricity.

View Manitario's profile


2630 posts in 2911 days

#5 posted 06-23-2011 05:40 AM

Vrtigo: Grandpa guessed right. My experience is that mini splits work well for moderate temps in smaller spaces; but if it is just cooling that you are after, get yourself a large, dedicated window A/C unit, I think that it’ll do a bit better and be cheaper for you.

-- Sometimes the creative process requires foul language. -- Charles Neil

View derosa's profile


1577 posts in 2863 days

#6 posted 06-23-2011 06:02 AM

I’d skip insulating the garage door until you are ready to add the A/C. Insulating the door will only deal with the ambient heat outdoors. Unless the door is black/dark blue there is very little radiant heat getting through, if it is white then the sunlight is having almost no effect. The biggest issue that warms up a room in the roof line, black shingles will cause the radiant heat to build up all day, a peak vent, soffet vents and properly installed insulation that allows airflow along the roof line will do plenty to reduce the temperature. After that the walls and door will matter. without dealing with the roof you will waste plenty trying to cool the space.
Other random semi-environmental option; paint the roof silver, add skylights to allow the hot air out and for free lighting and plant shade trees around it will also do wonders in the long term as will painting the driveway silver to remove radiant based heat at the door.

-- --Rev. Russ in NY-- A posse ad esse

View David Grimes's profile

David Grimes

2078 posts in 2667 days

#7 posted 06-23-2011 07:45 AM

My recommendations:

Wall Insulation: As long as you don’t have purlines in the wall studs, you can use a hole saw and blow cellulose in at the very top (dry and dense pack), then plug it back up with the hole you cut (bed tape and mud/sand etc.). If you do have purlines, then twice as much work for you.

On Cellulose versus Batted: “R-Value” (an expression of heat transfer resistance) is the standard for measuring insulation performance. At R 3.6 to 3.8 per inch, blown-in cellulose insulation is considerably better than fiberglass insulation which has an R-value of about 2.2 to 2.6. But R-value is only one factor in the energy efficiency of a home. Studies of actual buildings regularly show that cellulose-insulated buildings may use 20% to 40% less energy than buildings with fiberglass, even if the R-value of the insulation in the walls and ceilings is identical. One reason for this is the capacity of cellulose to stop air infiltration and heat-zapping convective air currents within your walls and ceilings, which are inherent with most fiberglass insulation.

I have personally witnessed a demonstration of cellulose versus batted in identical wall cavities with 100 watt light bulb heat source at the top, each of the insulations in the middle and Fluke thermometers below. The batted cavity’s heat kept climbing, but the cellulose remained ambient. I will not use batted except where cellulose can’t reasonably be used.

Garage Door: The kits all look like butt to me. If you have metal panel sectional doors like I do, you can get the insulated metal panels from a garage door supplier and they will do the job AND look good.

Good luck.

-- If you're going to stir the pot, think BIG spoon or SMALL boat paddle. David Grimes, Georgia

View Vrtigo1's profile


434 posts in 3019 days

#8 posted 06-23-2011 05:14 PM

Thanks for the replies, lots of good info.

Regarding the window unit – I would if I could, but since I have no windows I don’t see how that could work. Putting a spacer in at the bottom of the garage door is also definitely out for appearance and HOA reasons.

When I was reading about the cellulose, I didn’t understand that the R-factor specified was per inch. It makes a lot more sense now that I know that.

My south wall does have horizontal studs about halfway down, so it looks like I’ll be making a lot of holes. I called a few insulation places and the general consensus is that they usually suggest that people remove an entire 4-6” strip of drywall along the length of the wall. The reasoning behind this is that if you only make one hole, when you’re putting the cellulose in, the air already in the wall has no way to escape. So, that seems like a plan, but I’ll have to think about whether or not it’s worth doing all the work of moving everything on that wall away from it then ripping up and repairing the drywall. I’ve never done drywall work before, so it is a bit intimidating.

As far as the attic, that seems to be the area where I can make the biggest difference, and it’s also probably the easiest. Granted, I’ll have to tear out the OSB boards that are up there currently and move all the junk to storage somewhere else, but the insulation guy said I can get 10.25” of loose fill cellulose (which should equal R-30) up there for $325. Is R-30 good enough for an attic, or should I go higher? How does that price seem? Is it worth doing yourself? It seems like for that price, it’s probably not worth the trouble of renting the machine and figuring out how to use it if I only save $100.

Regarding my attic, I’m pretty sure I have perforated soffit around the entire perimeter of the house. When I’m in the attic, I definitely see light coming in from all of the soffit areas. It also looks like I have three 48” vents on each side of the roof. My house is about 2000 sf excluding the garage, so that seemed a bit on the low side to me, but cutting holes in my roof is definitely well outside my comfort zone. If the ventilation is really under where it needs to be, I suppose I could look at getting some quotes to increase it. Any thoughts there? Would more vents be better or would one or more of those little “spinny vent things” be better?

View Dan's profile


3630 posts in 2908 days

#9 posted 06-23-2011 06:56 PM

IMO Drywall is a complete pain in the ass to work with. If it was me I would tear all the drywall right off and start from scratch. I would use the fiberglass roles with the paper back and then rather then putting drywall back up I would use plywood. Plywood is a little more expensive but its much easier to work with then drywall. Plywood would also work much better for hanging stuff in the shop.

-- Dan - "Collector of Hand Planes"

View Gene Howe's profile

Gene Howe

10543 posts in 3456 days

#10 posted 06-23-2011 07:36 PM

Lots of good ideas here.
A concern for me would be the block wall. Even on the north side it will act as a heat sink. I’d be tempted to glue some 2X2 battens on it and insulate with the foil covered batts…foil to the wall. Then cover it all with 1/2” plywood.
A method of getting the heat out of the attic, assuming there is one, would also help. I use a whole house fan mounted between the joists in the ceiling and 24X24 vents at each gable end.

-- Gene 'The true soldier fights not because he hates what is in front of him, but because he loves what is behind him.' G. K. Chesterton

View Grandpa's profile


3259 posts in 2703 days

#11 posted 06-23-2011 11:46 PM

Gene the fan would work but it would also draw in the outdoor air and remove the conditioned air. It could be mounted in a gable end and a large vent could be put in the other end of the attic. Can’t you cut an opening to mount the air conditioner? Concrete blocks also cut. Cut a hole and case it in for that unit.

View Vrtigo1's profile


434 posts in 3019 days

#12 posted 06-24-2011 05:27 AM

Well, I thought about cutting a hole for a window, but the big problem there is HOA, in my neighborhood the houses are unfortunately very close together, so a window unit would be an eyesore to my neighbors.

To the point about the block wall acting as a heatsink, I’m not saying that I disagree, but I know that the rest of the house has no insulation on the block. It is a block home, and they just put furring strips on the block and put drywall over top of those. I took pictures of everything as it was being built so I’d have a reference later on. I’ve tried to add some low voltage wall boxes on exterior walls, and I had to cut them down because there’s only about an inch of space behind the drywall before you hit block. My house was built by KB Home, so it’s cookie cutter construction, nothing fancy or unnecessary. Anyway, the inside stays cool just fine and my electric usage for cooling the house isn’t too bad, so I don’t think the block wall is something I want to worry about insulating right now. That may be something I do in phase two.

View auggy53's profile


159 posts in 2708 days

#13 posted 06-24-2011 06:53 AM

i just finished my garage last year and all i did was drywall the walls and ceiling ,cut in 2 new windows . one for a 12500 btu window unit . i have a frame house with vinyl siding with insulation board under it . so i did not insulate the walls . one garage door is insulated in front , but garage door on the back is not ( yet) last week it was in the upper 90’s here and my garage stayed at 75 . in the cold months i use a salamander heat which i installed a thermostat from a baseboard heater to control the temp . i stay pretty cozzy most all year and the cost dont seem to be to bad either

-- rick

View David Grimes's profile

David Grimes

2078 posts in 2667 days

#14 posted 06-24-2011 07:58 AM

Dan is right on… IF you do remove the drywall (or even bugger it up getting the insulation in, just replace or go over it with plywood… but may I suggest using either T-111 or pine beadboard instead of regular plywood. You don’t have to have a shop that looks like the Unibomber cabin.

I have the rough sawn T-111 throughout my personal shop and garage. As Dan points out, it is great for hanging and will take bumps and tantrums better over the years than sheetrock.

FWIW I have used T-111 or beadboard in all (over 30) custom houses’ garages I have built over the years. I do not add $ for it over sheetrock since the materials + labor to install and trim is about that of sheetrock in the end.

-- If you're going to stir the pot, think BIG spoon or SMALL boat paddle. David Grimes, Georgia

View Vrtigo1's profile


434 posts in 3019 days

#15 posted 06-24-2011 02:52 PM

Thanks for the suggestions. I think I’m pretty well informed to make some decisions at this point. If anything, I should be ready to build a kick ass shop in 5 or 10 years at my next house.

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