Heat moves naturally from areas of high to lower heat within your house, and all the building materials used in your house either absorb heat or help to transfer it. If your home is heated, that hot air will continually try to move to the outside of your house, where the air is cooler. In the summertime, hot air from the outside will constantly try to flow into the cooler space in your house. Insulation works to prevent the transfer of heat.
How Heat Moves.
Heat moves in three ways: conduction, convection, and radiation. Each of these refers to the substance heat moves through to get from a hot area to a cooler place.
Conduction refers to heat’s movement through solid matter. If a material is said to transfer heat readily, it’s a good heat conductor. Metal, for example, heats up quickly when exposed to heat—making it an efficient conductor.
Convection refers to heat’s movement through liquid or gas. Our atmosphere encourages heat convection—you feel it whenever you hold your hand above a burning candle.
Radiation refers to heat’s movement through space. The light of the sun, for example, radiates over millions of miles of space to reach us.
When insulating a home, insulation must block conductive, convective, and radiant heat. There are many different types of insulation, and their effectiveness is measured by a regular industry standard called an r-value.
R-Value Explained.
An insulation material’s r-value refers to its ability to stop or slow down the transfer of heat. It’s based on a laboratory measurement, called an r-factor. The r-factor, multiplied by the thickness of the material in inches, gives you the r-value of the insulation.
Laboratory measurements, however, don’t always accurately reflect conditions in the real world. Most insulation materials lose their effectiveness when crammed into a tight space between walls. In addition, temperature can also make a big difference—some insulations operate better in colder temperatures, while others work best in warmer environments. In addition, if a material is stretched too thin or installed improperly, the r-value could diminish.
Types of Insulation
All insulation consists of air or other gases (usually hydrochlorofluorocarbons) in pockets of foam or fibrous material. Gases tend to conduct heat much more slowly than solid materials do, so they make better insulators—that’s why insulation can’t be packed too tightly, or it won’t work. There are several different types of insulation on the market today, and each has pros and cons. Here’s a breakdown of the most common types you’ll see.
Fiber. Fiber usually consists of fiberglass, rock wool, or cellulose with cavities of air. It comes in two forms: batts and loose-fill. Loose-fill fiber insulation is blown into the spaces within walls, and has the advantage of filling every inch of available space, working easily around pipes. However, loose-fill insulation does settle over time, creating empty spaces above the insulation where heat can escape. This can be countered by blowing the filling in tightly, creating high-density insulation—which can have the negative effect of reducing air pockets. It can also be mixed with water, creating a sticky substance that makes a more effective seal.
Batting doesn’t settle like loose-fill insulation does, and it’s much easier to install. However, it generally doesn’t fill a space as effectively as loose-fill does.
Foam. Foam comes in a spray form or in stiff sheets, and is generally more effective at blocking heat than fiber. That’s because instead of air, its pockets are filled with hydrochlorofluorocarbons. The downside is that this gas destroys the ozone layer. While it’s trapped in your insulation it does no harm; however, chewing insects can release the gases, and once your insulation has to be replaced, there is not really a safe way to dispose of it.
Reflective insulation. This blocks radiant heat instead of conductive heat. Reflective insulation consists of a reflective material that bounces heat back and keeps it within the house. Reflective insulation is generally greener than foam, as it doesn’t have the same problems with hydrochlorofluorocarbons.
The Importance of Insulation
Good insulation can make your home more energy-efficient—or it can leak the valuable energy you spend to regulate the temperature of your home. Which insulation you choose is an important decision, but it’s even more important to make sure you hire a reputable contractor to apply the insulation. Many homes have incorrectly-installed insulation that causes serious energy issues—and the owners can go years without realizing the problem. Your insulation can go a long way toward making your home greener and more energy-efficient.