Guide to Home Insulation

A look at re-insulating a house and making it more energy efficient. Types of insulation, techniques for installing it, and likely leaky areas are discussed.


| October/November 1993



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With winter around the bend, now is the time for a complete insulation overhaul.


ILLUSTRATIONS: MOTHER EARTH NEWS STAFF

"If the United States took the money... for the Middle East-aimed Rapid Deployment Force and used it for making buildings heat-tight, the resulting energy savings would eliminate the need for Middle Eastern oil imports—making the Rapid Deployment Force unnecessary."  

—The Rocky Mountain Institute

After reading the above quotation, I was reminded of the 1970s energy crisis when fuel prices skyrocketed for cordwood as well as fuel oil. So I surveyed the heat efficiency of our New England home for the first time in years. I discovered air leaks in the foundation, mouse-nest cavities in the attic insulation, loose caulk around windows, worn weather stripping on doors, and a cellar window that I must have left partly open all last winter.

If, like me, you've been taking stable fuel prices for granted, it's time to overhaul your home insulation. We must be prepared for the energy uncertainties of the '90s. There are new materials, new energy codes to satisfy; and the environmental effects of insulation to consider.

You'll recall from your school days that heat is a state of matter—a function of the speed at which molecules move. The more energy you impart to them, the faster they move, the hotter they get, and the more heat they release in any relatively cool direction. The fire in your wood-burning stove distributes heat in three ways: conduction, in which energy is transferred molecule to molecule from the firebox to the cooler outside of the stove; radiation, in which infrared rays excite molecules in your cold feet or the living room walls; and convection, in which air near the stove's hot surface warms, expands, and rises to circulate through the room.

Similarly, your house loses heat in winter and gains it during the summer via conduction (through frame, foundation, windows, and doors), radiation (from any warm surface), and convection (through air circulating in looping currents inside rooms and hollow walls, transferring energy from warm to cool wall surfaces). But the greatest heat robber of all is infiltration, which occurs when air escapes through leaks.

To reduce infiltration, seal the house. To reduce radiant and convection heat loss, impose energy barriers between living spaces and the outside—i.e., insulate. To complicate matters, you need to keep humidity in during winter and out during summer. However, you must prevent it from condensing inside cold wall surfaces, which rots wood and soaks insulation, rendering it ineffective. Install a vapor barrier between living space and insulation.





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