story by Samantha WittchenAccording to the U.S. Department of Energy, heating and cooling costs account for 50 to 70 percent of the energy used in a typical American home. In most homes—especially in the older housing stock so prevalent in Philadelphia—inadequate insulation is a leading cause of wasted energy. EnergyStar estimates that you can save up to 20 percent by insulating and air sealing.
Even if you’re sold on insulation, there’s a catch: It’s difficult to insulate an existing house, especially one with walls made of plaster applied directly to brick (typical in older rowhomes). In newer homes, drywall is typically applied to wood studs, and this creates a cavity to fill with insulation. Plaster and brick don’t allow for this, but that doesn’t mean you should give up.
The attic should be your first priority. As your mother always told you in winter: Don’t go outside without a hat! Heat generally rises in a house, so good insulation in your attic keeps heat in during the winter, and has the added benefit of keeping out the heat that beats down on your roof during hotter months. Most homeowners have some sort of access to their attic—whether it’s through a pull-down staircase or a ceiling hatch—so it’s relatively easy to install insulation up there.
Other targets for insulation include exterior walls, floors over an unheated space (like a crawlspace) and ductwork and pipes through an unheated or uncooled space.
So, let’s talk about R-values and types of insulation. Resistance to heat flow is described in terms of insulation’s thermal resistance, represented by what is commonly known as an “R-value.” The higher the R-value, the less heat flows through the insulation. For Philadelphia’s climate zone, EnergyStar recommends R-38 for wall insulation and somewhere between R-38 and R-60 for attics. For your attic, that equates to about 12 to 15 inches of insulation. If you’re going to insulate a floor, try to achieve somewhere between R-25 and R-30.
There are numerous insulation options out there, but unless you’re undergoing a renovation and replacing exterior siding or building new interior walls that have a cavity, your main options are blown-in cellulose insulation, blown-in fiberglass insulation or spray-foam insulation. Sorry, those cotton candy-esque batts you get at Home Depot aren’t an option. They’re virtually impossible to install in an existing house, and even in a new house, they’re difficult to install in a way that creates a good air barrier.
For blown-in insulation, you have two main choices—cellulose and fiberglass. Cellulose insulation is made of recycled wood fiber (primarily newsprint) and is available dry or in a wet spray. Dry cellulose is applied using a blowing machine, which you can rent at most big home improvement stores. If you go with a wet spray, you should hire an experienced installer. One of the early problems with cellulose insulation was that it settled over time, reducing the R-value, but those problems have been largely solved with newer technologies.
Fiberglass insulation is made from molten glass spun into fibers and typically contains 20 to 30 percent recycled content. Whereas cellulose insulation has virtually no carbon footprint, fiberglass insulation’s footprint is pretty high.
Fiberglass is also an inferior air barrier, so if you have any air movement through your walls, forget achieving the R-value that’s advertised. Fiberglass is generally rated at R-3 to R-4 per inch.
Spray foam also comes in two types—open-cell or closed-cell. Closed-cell (sometimes called “two-pound,” referring to the density) has a much higher R-value per inch—somewhere between 5.8 and 6.8—but it’s made from fossil fuels and is much more damaging to the environment. Open-cell (or “half-pound”) is either polyurethane or soy-based, and its R-values clock in at around 3.6 per inch. Spray foam is probably your most expensive option, and it needs to be installed by an expert.
The bottom line: The more temperate fall and spring months are the best time to insulate your house so you’re ready for the heating or cooling season. Additionally, the federal government is offering a 30 percent tax credit (up to $1,500) on the purchase price (excluding the installation costs) of insulation installed in 2010. So, whether it’s blown in or sprayed on, there’s no time like the present to insulate! ■