Energy costs fluctuate over time, but with overall trend always upward, homeowners are increasingly looking for different and additional ways to insulate the home and keep heating and cooling costs down. One area that is frequently examined is the garage—and specifically the garage door. A garage that is attached to the house and shares one or more common walls with the home itself can definitely be a source of heat loss, so evaluating the garage makes perfect sense.
The garage door on an attached garage is often seen as a weak link in the thermal envelope on a home, and for good reason. In most homes, the garage door opens several times a day, exposing most of an entire wall to outdoor air. It is like a giant window wall that isn't serving its function at all unless it breaks the thermal envelope in a huge way whenever needed. For this reason, efforts to seal and insulate a garage are thwarted by the very way a garage door functions. Unless the garage door is rarely used—which may be the case when a garage is used only as a workshop or living space rather than to store cars that move in and out—thoroughly insulating the garage often costs more than any energy savings you'll enjoy from doing so.
Still, people often feel that adding insulation R-value to the garage door is warranted and necessary. And in a few instances, this may be true.
Garage Door Insulation
Among solutions some homeowners try is to apply standard batt insulation to the inside of the door, or to spray foam insulation on the inside surface—the same kind of insulation sometimes sprayed against roof sheathing from the inside to improve the R-value in an attic. But garage doors are meant to function. They need to open and close on a regular basis, often hinging or folding at several different points. So neither bat insulation or spray foam insulation are going to work well on the garage door. Even if you find products designed for application against a garage door, the constant movement of the garage door will eventually cause them to flake, pull apart, and fail, which means that you're looking at insulating your door again and again. This is hardly cost-effective over the long haul.
If you are intent on an energy efficient garage door, a better alternative is to purchase a garage door that is already insulated. Rather than a metal door, which conducts heat and cold easily, choose a fiberglass door with a foam core, which will help stop some of the energy loss from the garage. If you're planning on replacing your garage door, looking into an insulated model is probably a good idea. But it probably does not make financial sense to replace an otherwise good garage door with an insulated model just for the energy savings potential.
Insulate the Rest of the Garage Instead
Garage door insulation is of limited value anyway, given the other areas of the garage that are equally problematic in terms of heat loss. The floor of your garage is probably built on a slab, which means that it isn't insulated and is an ongoing source of energy transference. If your garage has concrete walls, these, too, are constant sources of heat transference. If you take the time and spend the money to insulate the entire garage, you may well be disappointed by seeing a very minimal improvement on your energy bills.
Rather than attempting to insulate the garage door and other components of the garage itself, a much more effective solution is to focus your attention on the boundary walls between the main house and the attached garage. Put insulation into the ceiling of the garage so it helps stop the loss of energy to the space above, where it may connect to the house attic. Make sure there is plenty of insulation on the interior wall of the garage—the wall shared with the house itself. By doing so, even if the temperature fluctuates inside the garage, it won't greatly affect the temperature inside your home or raise your energy bills.
While most contractors will tell you to insulate the transfer points from the garage to the house itself, there are still times when you may want to further insulate the garage door, as well as the walls and floor of the garage. If you use your garage as living space, rather than as a storage area for cars and other items, then you may be heating or cooling the area anyway and the garage door may not operate much. In this instance, it does make sense to maximize the R-value of the walls, floors, ceiling, as well as the garage door.
This can be true of both attached garages and those that are detached and separate from the house. If you are supplying supplemental heat or air conditioning to a detached garage that serves as a woodworking shop, for example, you'll want to make every aspect of the garage as energy-efficient as possible. It has been shown that an energy-efficient R-18 garage door can keep the garage space about 12 degrees warmer in winter months and about 25 degrees cooler in summer, provided the rest of the garage is adequately insulated and sealed. But remember that an energy-efficient double garage door costs somewhere between $1500 and $2000, so it will take considerable time to pay back the cost of the door in terms of energy savings. And it really only makes sense for spaces where the garage door won't be opened routinely to break the energy envelope.
Another option where the garage will be used for living space is to insulate the door with a garage door insulation kit, available at home centers. There are two types of kits usually available. A vinyl-faced fiberglass batting kit provides a decent R-8 insulating value for the door; two kits will cover a standard 16-foot wide garage door. This type of soft insulation is simply taped to the inside surface of the door. Another option is to by precut expanded polystyrene (EPS) rigid foam panels and apply them to the door. The panels are simply cut to length and snapped into the space between the horizontal rails on the door panels. This type of kit provides an insulating value of roughly R-4.
Most people think of improving energy efficiency in terms of adding insulation, but the reality is that a large degree of heat loss occurs because of air gaps where drafts occur. Insulating a garage door and other areas of the garage will be of limited value if door gaskets, window weatherstripping, and other air gaps are providing places for air to flow. Always seal these areas when you are addressing the energy efficiency of a garage.
If you use your garage as storage for your cars and other items, you're probably better off leaving the door alone and insulating the ceiling of your garage and the walls that are shared with the home instead. If you use your garage as a living space, however, it's probably worth your while to insulate the door as well as other elements of the garage. Make your decision based on your lifestyle and needs.