Winterizing Your Home: The Chimney Effect
Your home is a living, breathing thing. There is always air moving in and out through the layers of construction materials. To some extent this is good, because people need fresh air. So do pets, plants and combustion appliances such as stoves and furnaces. However, problems arise when this air movement is so great that it's difficult to maintain a comfortably heated home.
Creating a tighter barrier against cold drafts is one step toward winter-proofing your home. Another issue to which you should give equal attention is the movement of air within your home. That is, from room to room and floor to floor, rather than from outdoors to indoors.
When air is heated, it rises, often right through the roof. These warm updrafts suck in cold air through the same gaps, openings and cracks mentioned earlier. Updrafts also cause backdrafting through plumbing-ventilation pipes and exhaust ducts, which means potentially hazardous fumes entering the living space. Updrafting contributes to the costly heating cycle by essentially turning your home into a great, big chimney.
Most important of all for controlling the warm updrafts is to have a tightly sealed and well-insulated attic. If you can keep the warm air from rising through the ceiling and out the top of your house, it's a sure bet that you will be more comfortable this winter. There are several things to look for when evaluating your attic.
First, make sure that the insulation is in good condition. If the insulation is dirty, take it as a sign of air leaks. You'll have to pull up the old insulation and seal any cracks you can find.
It's likely that warm air rises into the attic through cutouts for recessed lighting, plumbing vent pipes, furnace chimneys and electrical wiring. Caulk and expanding polyurethane foam are good for sealing these areas, and especially useful if you are making repairs to the topside of a plaster-and-lathe ceiling.
Make sure that bathroom ceiling fans are caulked in place. These sorts of cutouts in ceiling Sheetrock allow heat to escape into the attic. Once the leaky spots are sealed, it's a good idea to lay down a new plastic-sheeting vapor barrier that follows the contours of the joists.
If you don't have them already, install plastic baffles on the underside of the roof just above the soffit vents. The baffles keep the insulation from blocking the flow of air through the attic. This airflow is crucial for removing moisture, and care should be taken to maintain it. If you don't have adequate ventilation, consider installing new vents and baffles.
After the vapor barrier and baffles are in place, the insulation can be replaced or new insulation installed. It should completely cover the floor space without gaps and without being compressed. Fiberglass batt insulation is quite popular and easy to install.
Consider a blown cellulose insulation instead if you have an older home (pre-1950s) with a lot of drafts. Cellulose insulation can be sprayed directly into walls and in between ceiling joists. It flows over and around framing, filling cavities that are often missed by fiberglass batts. This creates a very dense and thorough layer of thermal protection and it is a great alternative to tearing out walls when you want to add insulation. You could rent the equipment and do this job yourself, but you'd probably be happier leaving it to a contractor, as things can get kind of messy.
The entryway to your attic is another potential trouble zone. Prevent warm air from rising through the hatch or stairwell by treating it like an exterior door, creating a good seal by using the same sort of weather stripping as on other doors.