If you’re looking to re-insulate your home, you’ve probably stumbled upon spray foam insulation as an option. If yours is an older home, you’re probably already somewhat aware of the lower R-value insulation found in older houses like yours.
If the insulation in your home is more than 20 years old, its effectiveness has deteriorated. If your house was built prior to 1984, it most likely needs more insulation.
Bofore you begin, you should have a good understanding of what R-value is and how it relates to insulation. You’re in the right place. Read on learn more about how insulation works and how R-values effect your energy costs.
HOW DOES INSULATION WORK?
Understanding how insulation works means understanding heat flow. Heat flow involves three principles: conduction, convection, and radiation.
Conduction, Convection, and Radiation
Conduction is how heat moves through materials. Think about how a metal spoon placed in a hot cup of soup conducts heat through the handle and to your hand. Convection is the way heat circulates through gases and liquids.
Convection is why warmer, lighter air in your home rises, and why denser, cooler air sinks.
Radiant heat goes in a straight line. It heats whatever is in its path that’s solid and can absorb the energy.
Insulation Slows Heat Flow
Most insulation materials slow down the conductive heat flow. It slows the convective heat flow as well, to a lesser extent. No matter which way heat moves, it flows warmer to cooler until the temperature evens out.
During winter, heat moves from your heated living spaces to your unheated attic, garage, basement, and eventually outside. Heat flow can also move through ceilings, floors, and walls via radiation.
During the summer, heat moves in the opposite direction, from outside to your home’s interior. The proper installation provides a resistance to the unwanted flow of heat.
HOW R-VALUES FIT IN
The industry measures insulation’s resistance to conductive heat flow by rating it according to its thermal resistance or R-value. The higher the R-value is, the better the material insulates. A high R-value, then, means higher effectiveness.
The R-value depends on the type of insulation, density, and thickness. For some types of insulation, the R-value also depends on aging, temperature, and moisture.
Location Affects R-Value
How well insulation resists heat flow depends on how and where you install the insulation. For instance, if the insulation has been compressed within the space, it will not retain the full R-value.
The R-value of an entire ceiling or wall differs from the insulation’ it self’s R-value. That’s because heat flows more easily through joists and studs via thermal bridging.
Different R-Values for Different Regions
The amount of insulation and R-value you need depends on your type of cooling and heating system, climate, and the part of your home being insulated.
Most places that sell insulation will have a map or chart indicating which R-value is recommended for your climate. The United States is divided into regions or zones. Energy Star has a recommended R-value for each zone.
This is cross-matched to the area receiving the insulation. For example, Energy Star recommends R-30 for a roof in the southern United States, R-38 for the middle of the country, and R-49 for the northern part of the country.
Here in DFW the recommended Energy Star R-value’s are R-60 for attic and R-21 for walls.
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