When it comes to insulating a finished, heated space such as a garage or storage area, there are certain considerations that need to be taken into account. Insulating all exterior walls, including walls between living spaces and garages, shed roofs, or unheated storage areas, as well as the foundation walls above ground is essential. The type of insulation used should be the same as that used inside the house in order to cover ventilation holes and reduce the amount of cold air entering the space and the warmer air leaving the space. It is also important to consider insulating the garage door, which has different installation requirements than walls or ceilings. In new construction, using construction techniques that provide both foundation structure and insulation, such as the insulation of concrete forms and the insulation of concrete blocks, is recommended.
Additionally, insulating and hermetically sealing the home's garage, foundation, and attic will have a greater impact on home comfort and temperature control. If your attic has enough insulation and a proper airtight seal, and your house still feels cold and drafty in winter or too warm in summer, you'll probably need to add insulation to the exterior walls. In most cases, a basement with insulation installed on its exterior walls should be considered a conditioned space. Choosing the right type of insulation and having it properly installed will keep your garage at a more stable temperature by limiting the transfer of hot and cold air from outside. It is also important to insulate and hermetically seal any wall in your house that is located next to your knees (vertical walls with attic space just behind them). If you haven't updated your attic insulation for a while, it's very likely that attic insulation, or the lack of it, will also contribute to your house feeling so uncomfortable and wasting energy.
You can insulate walls, roof, and garage door with the highest possible R-value (the higher the R-value number, the better the material's insulating efficiency), but if you can't fill the remaining air gaps, you'll still waste a lot of heat. If the air distribution is in the attic, consider insulating the beams so that the distribution passes to the conditioned space. Even in a house with an unconditioned basement, the basement is more connected to other living spaces than to the outside, making the insulation of the basement walls preferable to roof insulation. Also install an air barrier to prevent cold garage air from short-circuiting the insulation below the subfloor.
