Greetings Learned Forum:

After much give and take, I have come to the conclusion that I will be unable to heat my garage.  My hope had been to keep it at 50 deg. during our cold and long New Hampshire winters.  Assuming that the wall between the garage and the house will be thoroughly insulated and devoid of air movement, is there any point to insulating the garage walls and ceiling?  What about 2" rigid under the slab?  Someone said that pulling a hot car into a well insulated garage could raise the temp inside enough to do some snow and ice melting.  Or is this a whole lot of money wasted on unconditioned space?  Your thoughts and opinions are greatly appreciated.

NickB

Unless there is a room above or below the garage I would not bother to insulate. I have a unheated detached garage, if I need to work on a car in winter I just turn on the 60,000 btu propane radiant heater.

I've read at a couple sites including the LEEDs check list that you should have a fan that exchanges 3X the air space in the garage when a car enters or leaves a garage. It helps keep nasty gasses from entering your home.

I don't know that I will ever heat our garage but we insulated the exterior walls and ceiling and went down to the footings outside with 2 inch around the exterior. I figured with it all open I might as well insulate it in case I ever do want to warm it up, it's a lot easier to do it now rather then later.

I have heard rumors your better off not insulating the slab because it should stay closer to ground temp and slightly radiate in to the space but if you insulate it the floor will actually get colder in winter and warmer in summer. I don't know how much truth there is to that though.

Hello, and thanks for your replies.  To answer your question, Road Block, there is a room over the garage.  I will remain unfinished and uninsulated for the foreseeable future, and will be used as cold storage.  At some point, it may be turned into an in-law apt., but that is speculative and way in the future.  Brock, I know what you are saying.  If there was any way to heat the garage, I would do it now.  The reason I am not heating it is because I am going with geothermal heating and cooling.  To add in the garage pushed the budged hugely out of whack.  I ended up having to go with two separate heat pumps; without the garage, I can get by with one.  So I highly doubt I will ever be heating it.  I just wonder if I should insulate anyway, assuming it will always be unheated space.  I guess that is what my question boils down to.

NickB

NickB, what system are you going to use for cooling wf geothermal? Valance?

If you have a room above the garage, even though it is not heated I'd insulate at least the ceiling of the garage. That room above is connected by a wall and door to the rest of the house and will suck the heat out of the house. I'd also insulate the common wall between the rest of the house and the room and do something with the door for insulation and air infiltration.

A friend of mine had a bedroom over the garage, the garage ceiling was insulated with fiberglass batt and that room was always cold, you felt the cold rolling down the stairs.

Nick are you doing in floor heating in the rest of the house? Even if you don't size the Geo for it I would put the tubes in the floor. Again not a huge cost right now and at some point later you might have extra heat to heat with or maybe add some other source, solar hot water or who knows. As the rest mentioned since there is a potential living space above, it is another reason to insulate it all. The warmer the garage is the warmer that space will be and the warmer the garage the less heat you will loose from the house to the garage as well.

  Someone said that pulling a hot car into a well insulated garage could raise the temp inside enough to do some snow and ice melting.  NickB, I live in northern Wyoming and I have an (2x4 framed/fiberglass batt including the ceiling)insulated, unheated garage(but it does have a chest freezer adding a little heat) and I can say that in my opinion, it is not wasted money to do so because: 1. The snow does melt off when you pull in a heated vehicle. 2. Even though the common wall with the house is insulated, there is still a temp difference to the garage, and therefore a heat loss. The garage acts like a giant buffer to the elemnts, and the insulation will hold the temp somewhat above the ambient outside temp.. 3. If the garage is insulated, all you need in the winter to make it tolerable is a very small electric radiant heater(floor unit). I did not insulate under the slab so I can't offer advice based on experience, BUT the ground temp is only "warm"(55F) after you get 6, 8, or 10 feet deep into the ground, like you would be in the basement. The temp of the soil directly under the garage slab is not likely to change the temp of the garage much. My $0.02 worth. Hope it helps. Dave

I have used different products under a slab to keep the cold from infiltrating in to you conditioned space. Both with excellent results. A lot better than using EPS or blueboard. Also a lot faster installation with less hassles to use.

http://www.thebarrier.com/

http://www.insulationsolutions.com/products.html