Saving money on energy bills is a good thing, especially in very warm or cold climates where the AC or the furnace have to run a lot. It can costs hundreds of dollars a month to make the living space comfortable. However, the garage is a different story. Trust me, I found out the hard way. I will never recoup the money I spent insulating it, and on very cold days, the paint and other supplies still get ruined.
Here in Colorado, temperatures can drop into the single digits. My goal was to keep as much heat from the car engine in the garage as possible. I just wanted to make it a little more comfortable and hopefully keep the temperature above 32°F so paint and other stuff like caulking tubes wouldn’t get ruined.
I spent about $1,500 insulating the walls, ceiling and the door itself. I knew I wasn’t going to make it super warm like inside the house, because I wasn’t actively heating it with natural gas or electricity. In the end, I can tell you, it was a waste of money for me.
Bottom line is, unless your garage is heated, insulation will have little affect on the temperature inside your garage in cold climates. Just because you add insulation won’t make the garage that much warmer or cooler.
The main purpose of insulation is to slow the conduction of heat from the walls and ceiling to the outside and vice-verse. Insulation by itself does not generate heat. If your garage is already cold, the area will virtually remain the same temperature whether you have insulation or not. And remember this, when you open your garage door, you recycle the air in a matter of seconds then trap the new cold air until you open the door again. And no, things like a refrigerator, freezer, or lights will not heat the garage to make the insulation worthwhile. In warm climates, it may be worthwhile, but I don’t live in one so I couldn’t tell you.
Now if I spent a lot of time in the garage and added a heater, that’s a totally different story and I would probably see a big difference. In that case, insulating the garage is definitely worth it because I’d want as much of the heat to stay in the garage for as long as possible (running a heater costs a lot of money).
Some have argued that the wall(s) which separate the main house from the garage will allow some heat to pass and thus warm the garage, but that shouldn’t be the case! The walls which separate the garage from your main house should be insulated to prevent as much heat as possible from conducting into the garage from the house. If those walls are not insulated or not insulated enough, such that your garage is warm without a heater, then that is something I would fix immediately so as to retain as much heat as possible in the living space of your house where your heater is working hard to keep it warm. In that case, adding more insulation may be necessary, which will save you money.
Now, if you do want a warm garage, then I would add a heater and insulate the ceiling, walls, and garage door just like you would inside a house. Depending on the size of your garage, insulating the walls with batts of R-13 will typically run you about $400, the ceiling $600, and the garage door will cost about $600 if you do it right (See image to the left). You can use the pink Styrofoam stuff from Home Depot, but that will only insulate your door to about R-6. If you spend a lot of time in the garage, buying a whole new insulated garage door might be better, but it will cost you about $1500 alone. So if you do just the walls and the ceiling, it’s probably going to run you $1,000. A bit pricey if you don’t spend any time in the garage.
But before you do anything, the best way to make your garage a little more comfortable is to stop any cold air infiltrating into your garage from the outside. Put new weather-stripping down where the garage door makes contact with the ground. If you have a door entrance from outside into the garage, make sure the seal is intact and no air is coming in around the frame. Use expanding foam to fill in gaps. These are good first steps that will only cost you about $80 and can make quite a difference. Even a slight draft can make your garage feel much colder than it really is, especially when it’s 10°F outside.