Quest against the cold

Home, shivery home
My wife and I purchased our first home in 1979 when I was employed by General Electric Co. in Schenectady, N.Y. Built in 1952, the tiny two-bedroom, brick-faced ranch home cost us $37,000. We probably got such a good deal because the seller’s husband had recently committed suicide in the garage and a bullet hole remained in the door window. No kidding. After replacing the window, I quickly went to work making the place more energy efficient, realizing that the only insulation in the house was a 3-inch layer of old mineral wool in the attic. I added an R-19 fiberglass blanket over the wool and we bought a wood stove for supplemental heating that first winter. Even so, we spent a small fortune on heating oil.

Resistance isn’t futile
A fellow engineer at GE showed me a simple way to predict home heat loss by modeling the building envelope as a collection of thermal resistances—much like an electrical circuit where the resistances represent heat-loss paths through the attic-roof assembly, walls, windows, doors and floor.

The analysis indicated where insulation was most needed and, more important, it revealed the so-called law of diminishing returns when you over-insulate. For example, adding extra insulation in the attic will have little effect on energy bills if most of the heat is escaping through uninsulated walls. Insulating the walls may shift the primary heat loss to the windows, and so forth. In the end, it’s important to address all building-envelope components to achieve maximum energy savings.

Cold crusader
I continued my energy-efficiency quest by insulating the wall cavities with blown-in cellulose (recycled newsprint). This required drilling 72 one-inch holes through the brick facing into the empty stud spaces. I remember patching the holes and hoping the effort would pay off. It certainly did. We got by on just two oil fill-ups during that second winter. In our California climate zone, where both heating and cooling loads are significant, residents can save between 15 percent and 25 percent in energy costs by insulating empty wall cavities.

After insulating the walls, my thermal model indicated that the leaky storm windows were now the weak link. I also did a little more research on homes and found that my model was missing an important element—air infiltration and the effect of weather stripping and caulking. I could go on and on with this energy retrofit saga …

On the Web
Sure, I realize that “normal” folks probably aren’t going to develop heat-transfer models. There’s actually no need to do so. Building researchers at universities and several Department of Energy laboratories have done the heavy lifting for us with the aid of some very sophisticated computer software. They have developed energy-saving best practices for both new-home construction and retrofits for the different U.S. climates. These design guides give recommendations for envelope retrofits, insulation, windows, flooring, roofing and ventilation. The DOE also has a handy ZIP-code insulation calculator.