Why Are Attached Garages Energy Inefficient?: A how to improve your garage guide to reduce energy costs
A Houston home inspector looks at steps to a green 
home conversion
Have you had a moment of epiphany? You look at something and say, oh, yes that makes sense. I had such a revelation recently when I was in a meeting with other home inspectors. We were discussing factors that make a home green, construction methods of such homes, and the current programs that define a green home. Most of these discussions revolved around the upcoming code, the ANSI 700, which will help define many of these ideas. We were also looking at the Green Home Verifier program for home builders, which can be a good business opportunity for home inspectors. At one point, our talk dealt with the idea of the building envelope and how it effects energy use. This led to a focused consideration of attached garages.
My home has an attached garage, about half the homes in my neighborhood have this arrangement. I was inspecting a home in a subdivision where all of the houses had attached garages. It is a great convenience. The space can be converted into another room. I use one bay as a play area for the kids when the weather turns wet. However, I have seen people create family rooms from their garages, since they leave their cars outside. Storage is a big deal for many. I have at times taken jobs organizing garages for people. With the remodeling of my home, my space is filling up with old furniture that we will eventually be sending to family in Mexico. Sometimes it becomes a work area. I have a ’64 Beetle that I am restoring in the other bay. Mainly, I think most of us use this area in our home as a catch-all for everything that cannot fit in the home proper.
When this space is being built, it is not treated like other rooms inside the walls of the building (the envelope). The attic above is not insulated. Rarely is natural light used. Then we have the doors to allow the cars to enter that also allow the cold wind to blow into that area. During a Houston summer, the garage becomes unbearably hot, because there is no air movement through it. During the winters, the garage can feel colder than the exterior, with no sun to warm the surfaces there. Yesterday morning, as I was taking the trash out, I stopped to look around the space. I had not turned on the lights. Around the side door I could see streams of light. The garage doors allowed a good deal of light to flow through. I felt the chill from the night’s near freezing temperatures linger. Now consider what is happening to your home.
Imagine a cooler that you use for your picnics. If you have placed an item from the refrigerator inside of it, and you have kept the lid closed, the interior of the cooler stays quite cool for a good while. This is the idea behind insulating your home. Super insulated homes can be heated or cooled with little energy. Now cut out a corner of this cooler. Place a cardboard box into that space. You have broken the envelope of the cooler, but you do have a wall between the cooler area inside the chest. Warm air in the cardboard box does eventually move into the chest, which causes more energy to maintain the temperature in the cooler. This is the same principle behind the attached garage breaking into your envelope.
Taking steps to prevent this energy loss is not too difficult. If your house is like mine, you will have attic space above this space. Insulate this area like you would the other areas of your home. My favorite insulation for a do it yourself project is batts sheathed in plastic made by Johns Manville. Loose insulation is great for certain areas, but to achieve good coverage, you need to blow it in. Other types of batts work perfectly well; however, the exposed insulation will be exposed to your skin. The batts covered in a sheath help reduce this discomfort. Covering the area in the attic is not too bad, even in a low roof like mine. The garage door presents another problem though.
There are two steps to dealing with the door. First, the easier procedure is installing a door seal around the sides of the door. This is a gasket material which can be tacked into place with nails. A lip of the seal fits against the door when closed preventing drafts. It took me about forty-five minutes to seal two doors. Here is the fun part. Like many people, I have a metal door with two foot wide panels. They are four inches deep. I do not want to add too much weight, and I am looking for a product that is readily available. I have seen insulation that would fit, but most home centers have batts that would fit in a sixteen inch stud space, which leaves eight inches to fill my bay. These are the batts that are R13 in value. Any larger than this number, and the batts are too heavy. You do not want to add much more weight, because this will cause problems with the system that allows you to open the door.
Since I wanted to have the R13, I went with batts, cutting pieces to fit into the extra space. I used wire to hold the pieces into place. If I did not want to go this route, I did have other options. There are 4×8 feet sheets of insulation that you can cut to fit into the spaces. These sheets are about an inch thick, and they equate to an R3. Do you use one of those insulating covers for your car’s front window to reduce heat? Well, that product is made for the home. It is mainly used in the attic, but placing it on garage doors gives you about an R8. It is also simple to cut, and you could glue it into place. To be honest, I think that these last two options are best for most people. They add less weight, and they are faster to install.
I am considering adding a window to this space. I like the idea of not having to turn on a light when I am just passing through this space to the side exit door, or if I am getting something that is stored there. Placing a window in the garage door would not be hard. I could cut out part of a panel to be replaced with plexiglass. Another option would be to add a window into the side door. Going through the wall takes more effort. You have to remove the exterior wall; expose the framing on the interior, so you can reframe that area for a window. Not a simple diy project. Looking at the side door, I realized that most of these doors do not have weather stripping or insulation strips around them. The peel and stick thin insulation strips are the easiest for this task.
Lastly, you may have created an insulated space, but I would still treat the walls inside your home proper which butt up to the garage as exterior walls. In a previous post about insulating to be green, I mentioned the foam insulation pieces that can be used behind outlet covers. If you just used these on the exterior walls, you may have skipped the walls adjacent to the garage. I did. The garage space is still not conditioned, so try to isolate it from the home with this action.
In all, I spent under two hundred dollars on this project for a two car garage. What will be the benefit to my energy costs? I have not exactly calculated that amount. I think that it could equal the savings that would be achieved by installing CFLs in your house. In a few years, the energy cost savings will pay for the project.
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