Lucas Hamilton is Manager, Building Science Applications for CertainTeed Corporation
Many of our houses have attached garages which are, for the most part, unconditioned space within our habitat. It is the interface of these two spaces which so often fails in our attempts to conserve energy and have superior indoor air quality.
For starters, you have to make sure that the garage is air sealed from the rest of the structure because of what you store in that space. You store things in your garage because you want them out of the weather but you don’t want them “indoors.” Very often negative pressure is generated in the home by exhaust fans and dryers. In your home’s attempt to reach a neutral pressure with the exterior, it will often pull air from the garage into the home. Now all of the gaseous and particulate contamination which is associated with what you are storing and doing in your garage is coming into your home. Think about what is on the other side of these “interior” walls – typically they are the rooms where we spend the most of our waking hours; kitchen and family room. If the separation plane between these spaces is not made air-tight we might as well move into the garage.
One small detail which is best addressed during the time of construction is breaking the continuity of framing chases between the garage and the house typically found in the garage ceiling. As the second floor framing runs continuously across one of the garage interior walls, air-tight blocking needs to be installed between floor framing to close this avenue of air migration. This is obviously easier to achieve with dimensional floor framing or “TJI” (Trus Joist I) than it is with modern trusses. Also ensure that any doors leading from the garage to the living space are properly sealed and air tight. Get a new door sweep if the old one is worn out. One great indicator of an air leaky passage door is a dirt “shadow” in the carpet just inside the sweep. Carpet fibers make excellent air filters and atypical soiling patterns are great indicators of air flows.
Once you’ve decreased uncontrolled air flow between the home and the garage is there added value by adding an insulated exterior garage door? Absolutely! Any way that you can tighten or insulate the envelop will improve the efficiency. When you are making any changes with regard to air tightness in the home don’t forget to include the garage in your decisions.