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Daox 08-20-09 09:55 AM

Insulating the garage
I had started a thread on heating my garage this winter. I guess that was a it premature as it still needs to be rewired (existing wiring leaves something to be desired) and insulated. It is standard 2x4 construction and I'd like to get as much insulation into it as possible. However, I'm unsure what the standard procedure is for garages. I'd like to get more than R13 or so fiberglass in there. I'm currently thinking that I'll put some rigid foam insulation over the fiberglass and then some OSB over the rigid foam insulation. I'm not sure how thick I can go, and this would also mess up electrical recepticals I'd imagine as they'd need to be moved outward to mount flush with the wall. I also don't know what I'd need (if anything) for vapor barrier.

Any advice or ideas are welcome. :)

Higgy 08-20-09 10:21 AM

I would either go with Roxul insulation which is rated R14 for 2x4 studs and forget the rigid foam overtop...cause then if you ever need to get to the electrical, you'd have to cut through the rigid foam or take it down somehow since your garage probably has older electrical in it...maybe not. I'm no electrician.

You could also just stick in 3 or 4 inches of rigid foam and forget the bat insulation altogether. Then you can just cut out the area for the wiring. Not sure if you'd still have to vapor barrier it if you do it that thick...I think that's only for spray foam that you don't need it if it's over 2.5 inches.

I'd also make sure you have 2 vents, one on each side of your garage to allow air to pass through and keep the air moving in there.

Daox 08-20-09 12:24 PM

That is true, I would have to cut through the insulation. But, if I went with spray in insulation, I'd never be able to get at everything. I'd have to carve the stuff out if I needed to get at it.

truckncycle 08-20-09 02:27 PM

If you wanted to use spray in insulation and you didn't know your future electrical requirements, you could always run rigid conduit. You can get it in metal or pvc. My suggestion is to add a bunch of 20 amp outlets. You can either add a gfci breaker or control all of the outlets off of an upstream gfci. An extra outlet in the ceiling might also be good. I have an air cleaner that is attached to the ceiling. I would also run at least one 220 outlet so that you can run more powerful tools. I ran 10 gauge wire for my outlets so that I would have more power available. It was a PAIN to run since it was so hard to bend. Multistranded wire would have been easier.

Daox 08-20-09 02:42 PM

Oh, I'll definitely be wiring in a lot of outlets. I'll be sure to include a couple 220 outlets too. Thankfully, my father in law is a master electrician, so doing the electrical isn't a problem. I am open to suggestions you guy might have though.

That being said, I'm really not too concerned about future electrical needs. I should be able to allow for most of what I need/want when I do the electrical this time around.

I love the idea of spray in foam insulation. The only draw back is cost. This is an unconditioned non-living area so I don't want to go too hog wild on it as there are plenty of projects left to do on the house itself.

TimJFowler 08-21-09 02:45 PM


Since you're retrofitting and want/need a good "bang for buck" ratio I'd suggest:

1. Run conduit and rewire for everything you can imagine wanting or needing.

2. Insulate the foundation perimeter to reduce the garage slab heat loss. I know how cold garage floors can be in the winter and limiting the heat sink effect should help. A large carpet remnant can also really help with increasing comfort in the garage.

3. Run 2x2 stringers horizontally across the 2x4's ( install insulation mesh, blow in (borate-only) cellulose insulation, install drywall.

That should make your garage MUCH warmer and more comfortable in the winter for a reasonable cost.


Daox 08-21-09 03:09 PM

Hmmm, very interesting idea Tim. I really like that idea! Its cheap and will give a nice high r-value (and next to no thermal bridging). I think we have a winner.

Has anyone here ever done dense pack cellulose? I've heard it both ways, its easy or hard to get right.

I've really thought about insulating the foundation perimeter. I've even asked around about it. The local guys say it won't do a lot. I'd have to agree with you though, it has to help. I always have hydronic heated floors in mind for the garage to make it super comfortable too, and insulating that is a challenge I think about too.

Daox 08-24-09 11:30 AM

I moved this thread into the projects section because I just started cleaning up the garage this weekend.

The first I thought that needed to be done was wiring. The current wiring needs a lot of attention. All three of the outlets in the garage are on the short wall of my rectangular garage. This is a real pain. So, I'll be putting 110V outlets all the way around the garage as well as probably adding a service panel and 220V for larger tools.

So, I started pulling things away from the walls to get in there for wiring. However, this also brings up another issue. The builder of the garage admitted to making it as cheap as possible and said he didn't do a good job. As you can see, there is plywood on the corner, but the rest is all particle board... So, it seems my first step isn't just going to be wiring, but also putting plywood, and house wrap (tyvek) on the outside.

My question to any of you guys is, do you think I can get some rigid foam on the outside? I'm thinking even 1/2" would be better than nothing. I am not wanting to get new siding, so I can't go real far here.

Here is the inside of the garage after some moving stuff around. This is where the electrical comes in.

More particle board...

Back to plywood in the corner, and then back to particle board. I'm also gonna have a fun time removing all those build in shelves to wire and insulate.

This is a close up of where the power comes in. The metal box is just jammed packed with wires. I definitely need a service panel out there. I wouldn't mind my stuff being grounded either!

I also got bad news the other day. My master electrician father in law is super booked up atm. He probably won't be able to help out with the project. :( That means I got a lot to learn about wiring in the next few weeks! Thankfully, I do have a book on it. I got "The Complete Guide to Wiring" by Black & Decker from the in laws for Christmas. It seems to be alright so far, but I haven't read too much yet. Plus, I'm not too intimidated by wiring recepticals and switches. I just don't really know how to do the service panel, but that should be too hard.

truckncycle 08-24-09 01:55 PM

Is the garage electrical on its own sub-panel or does it come from the house? Where does the main power come in?

That is a scary looking connection above. When I added a bunch of circuits to the house, the inspector said that one of the most common problems that he sees are boxes with too many wires for the size. Junctions outside of boxes are a problem too. I think that I have that same book. It was pretty easy to follow. Electrical work seemed really straight forward. One thing that the original electrician did that was helpful was to run one large empty conduit from the panel to the attic. This made adding my circuits a lot easier.

Daox 08-24-09 02:46 PM

The garage power comes from the house.

Yeah, that is a bit of a scary connection, and that isn't the only one either.

The book is clearing up a bunch of little questions I've had so far. For any other questions I'll just give the father in law a call to see what he thinks.

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