Homes lose heat through their sidewalls. Many older homes, built before sidewall insulation had been invented or perfected, are candidates for this upgrade. Measured in square footage, the sidewalls in most houses represent the largest exposure of any area to the outdoors. So it makes sense to make them as resistant to heat flow as possible.
Several different materials can be used for sidewall insulation: cellulose fiber, fiberglass, and a number of different types of foam. Each will not only retard heat flow from the inside of the house to the outside but will also cut down on air infiltration through gaps in the sheathing and other areas. Some foam products can be injected into sidewall cavities even if there is already insulation in place.
While sidewall insulation can be installed from inside the house through holes drilled into plaster or drywall, the usual protocol is to do it from the outside. This tricky job is best left to the experts.
Injection holes can be drilled through wooden clapboard siding and then plugged with paintable plastic caps, or some lengths of the siding can be removed and then replaced after holes have been drilled through the sheathing. Holes in stucco-sided homes can be patched with stucco-cement materials, and vinyl and aluminum siding can be temporarily removed and then replaced after the insulation-installation process is complete.
The Garage and House Interface
Homes with attached garages often have "interface" problems that can lead to waste of heat and cooling. Because the garage is attached to the house, in many cases the effort that goes into insulating the outside of the house against the weather is not extended to the garage. That's a mistake, because in the winter the garage can become just as cold as the outdoor air -- and in the summer, even hotter than it is outside.
There are often holes in garage walls, either put there intentionally or accidentally, that allow air movement between the two areas. Not only are these potential pathways for heated or cooled air to escape or infiltrate, but they are also a danger.
The shared wall between a house and garage is required to be fire-rated. That's so a fire that starts in the garage will be contained there for as long as possible before it breaks through to the house. Garage fires are more common than many people think; car batteries develop short circuits, and gasoline is often stored in cans for use with lawn mowers and other yard maintenance equipment. A hole in a wall between a garage and house can compromise fire safety.
There is another hazard that can involve a leaky shared garage and house wall. That has to do with carbon monoxide. An automobile produces a tremendous amount of carbon monoxide gas, especially when its engine is cold, as it is when first starting up. If you start your car in the garage in the morning and then pull it outside, shutting the garage door traps a large volume of carbon monoxide inside. This deadly gas can leak or be pulled into the house if there are pathways in the shared wall that allow it to infiltrate.
The solution is to make every effort to seal up areas where air might be able to pass between the house and garage. Prime locations are the bottom of the wall inside the garage and the bottom of the doorway into the house. There is a juncture between the framing and concrete where the bottom of the wall meets the concrete foundation that is similar to the one around the perimeter of the rest of the house. This location sometimes lacks a layer of compressible foam between the two materials that would provide an airtight seal. Caulk or foam applied either inside the basement (as previously described in the section on sealing this seam) or in the garage can effectively seal the gap.
It is also worth using caulk or foam to seal the bottom edges of the drywall to the concrete. The reason? In negative pressure situations, air can be drawn into this crack or into the stud cavities inside the wall, and then it can enter the house via an electrical receptacle in that wall inside the house. For instance, negative pressure can occur when the kitchen vent fan is running. That forces air out of the house, and as a result the atmospheric pressure inside the house decreases. The pressure seeks to equalize by drawing air into the house through any opening it can. If the path of least resistance happens to be that crack along the bottom of the garage/house wall, the incoming air can bring carbon monoxide along with it. Adding gaskets to receptacles on both sides of the wall also helps in keeping contaminated garage air out of the house.
The door into the house from the garage is often a leak point as well. Caulking around all the trim and an examination of the door's weatherstripping to ensure that it is intact will help block off this potential air passageway. Frequently used doors like the one from the garage into the house might need repair or replacement more frequently than do other entry doors.
Attics are another prime area where homes lose heat. Over time ice dams can form on your roof and cause damage. In the next section, we'll discuss how that process happens and what you can do to prevent it.