Saturday, November 08, 2008

Batting in the Belfry

Published: November 5, 2008

WITH energy prices having gone from bad to worse and back to just bad in the last couple of months, homeowners are more determined than ever to find ways to save on heating bills.

Erik S. Lesser for The New York Times

sheet by typing “Insulation Fact Sheet” into the search box at the home page of

“And the part of the house that most people can do something about is the attic,” he said.

The television host Bob Vila said that houses built 20 to 40 years ago probably have fiberglass insulation 6 to 9 inches deep, either blown in or in fitted batting, between the attic floor joists. But that does not produce a high enough total R-value, he said, referring to the measurement of a material’s ability to resist heat flow. So most houses probably need more insulation.

There are a couple of options. One, he said, is to blow loose insulation — either cellulose or fiberglass — over the top of the existing insulation. Most home centers will lend a machine to blow the insulation from outdoors, where it is loaded, up through the house and into the attic. The insulation itself costs about $11 a bag for cellulose and $27 for fiberglass, but the ultimate cost to the homeowner is about the same, as fewer bags of fiberglass are needed. A 100-square-foot space would need about 2.5 bags of cellulose or 1 bag of fiberglass.

Another option is fiberglass batting, precut lengths of fiberglass insulation that fit between floor joists.

Gale Tedhams, of Owens Corning, a fiberglass-insulation manufacturer in Toledo, Ohio, said that for most houses, attic-floor insulation should be 19 inches deep if batting or 22 if blown. “Adding what you need is very easy,” she said. Usually, she said, it is best to apply “unfaced” batting perpendicular to the floor joists. Faced insulation has paper or foil on one side as a vapor barrier. If insulation is already there, unfaced is better to use to avoid condensation between barriers.

Owens Corning retailers also sell loose fiberglass and provide a machine to install it, the AttiCat, which is free if part of a promo- tion or up to $100 a day to rent, based on how much is needed.

If the attic is a living space, it is necessary to insulate between the roof rafters instead of the floor joists. The traditional way is batting; another option is spray polyurethane foam insulation.

Alex Wilson, the president of BuildingGreen of Brattleboro, Vt., said there are two types of spray-on polyurethane: closed- cell and open-cell. Closed-cell is mixed as it is sprayed and then quickly expands to fit. Open-cell, a newer product, is also sprayed but expands even more. Closed- cell is about $1.20 for a one-inch- thick square foot, including prof- essional installation; open-cell, half that. Open-cell has a slightly lower R-value, but Mr. Wilson said it is comparable to closed- cell, since a thinner layer of closed-cell is usually applied.

Open-cell is available in a slow- ly expanding form that can be poured into a cavity and used to retrofit uninsulated walls in ex- isting buildings. Whatever is used, optimal insulation is a must. “The price gyrations over the last couple of years have de- monstrated how vulnerable we are,” he said, referring to fuel. “We just can’t depend on low prices sticking around anymore.”

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