You’re in the process of building your dream home and your contractor starts tossing around the term “R-value.” Just like other terms related to home buying and construction that seem mysterious, R-value is incredibly important, both in terms of the physical home and your understanding of what it means.
What is R-value?
Also called “thermal resistance,” R-value measures how effective insulation is at preventing the flow of heat into and out of the home. The higher the R-value, the greater the insulation performance. The greater the insulation performance, the more money you save on your heating and cooling bills. Many factors affect R-value, including where a home is located, geographically.
How does insulation work?
Insulation works by stopping heat from moving around and into/out of your house. Without insulation (or proper installation), heat will flow into the cooler areas of your home until a temperature equilibrium has been reached. In the summer, insulation helps keep your home cooler by resisting exterior heat; when a home is properly insulated, your AC won’t be constantly running, and your electric bill won’t be so expensive. Whereas in the winter, your insulation’s job is to prevent heat from escaping.
How is R-value determined?
The R-value of insulation is determined by a number of factors, including thickness, density, material, how it ages, and moisture accumulation. For spaces with multiple layers of insulation, R-value is equal to the addition of each layer.
How do I determine the R-value my home needs?
When constructing a new home or replacing insulation, it’s important to note that the highest R-value possible is not necessarily the best one for your home; the proper number is dependent on where you live and climate in that region.
The U.S. Department of Energy has a geo-map that breaks the country down into regions and specifies the R-value that’s best for homes in each climate. The differences are mainly determined by humidity, temperature changes, and other weather-related factors. For example, a home in Maine where there are distinct seasons and widely varying temperatures will have a different ideal R-value than one in hot, humid Louisiana, or a house in the Arizona desert.
When building your home, consult this geo-map to determine the R-value you need to achieve. Once you have that number, make your decision based on insulation type/material and where in the home that insulation will be.
What are the different types of insulation?
According to the U.S. Department of Energy, “the most common types of materials used for loose-fill insulation include cellulose, fiberglass, and mineral wool,” all of which are made from recycled waste. Cellulose often comes from old newsprint, whereas fiberglass is usually 40-60% recycled glass.
In addition to loose-fill insulation, which is also called blown-in insulation, homeowners can opt for insulation blankets, spray foam, foil, or foam board insulation. Each type will resist heat in its own way. Bulky material like fiberglass will block heat whereas rigid foam will trap air, thereby resisting heat flow.
How do I choose insulation?
The material you choose should depend on where the insulation will go as well as the R-value you want to achieve. You can mix and mingle the types of insulation in an area to reach a higher R-value. Other factors to consider when making a decision are indoor air quality and infiltration, humidity, wind, outside temperature changes, cost, ease of installation ( if you plan to do the installation yourself), and embodied carbon.
Generally speaking, a higher R-value yields the best climate control and energy efficiency, but it will also cost more. However, that upfront investment will save money in the long run due to more manageable energy and electric bills.
Where is insulation needed in my home?
Common areas to fill with insulation are walls, ceilings, and crawlspaces. If your home has a basement and/or attic, insulate those as well. Other spaces that are often overlooked in home construction but should still be insulated are garages, water heaters, and water pipes.
The R-value of each of these areas will vary. The attic, for example, will have a different R-value from a 2x4 wall or your home’s crawlspace.