You’re in the process of building your dream home when your contractor starts tossing around the term “R-value.” As is true of other mysterious terms related to home buying and construction, your understanding of R-value is important.
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 a structure. The higher the R-value, the greater the insulation performance. In terms of your home, the greater the insulation performance, the more money you save on heating and cooling bills. Many factors affect R-value, including a home’s geographic location.
How does insulation work?
Insulation works by stopping heat from moving around and into/out of your house. In the summer, insulation keeps your home cooler by resisting exterior heat, and in the winter insulation’s job is to prevent heat from escaping. Without insulation (or its proper installation), heat will flow into the cooler areas of your home until a temperature equilibrium has been reached, while a properly insulated home doesn’t need the AC or heat to run constantly, saving you money on your electric bill.
How is R-value determined?
The R-value of insulation is determined by a number of factors, including thickness, density, the material it’s made of, how it ages, and moisture accumulation. For spaces with multiple layers of insulation, R-value is equal to the addition of each layer.
When building your home, consult this geo-map to determine the R-value you need. Once you find that number, make your decision based on insulation type, material, and where in the home the insulation will be installed.
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, while rigid foam will trap air and resist heat flow.
How should I choose insulation?
The right material depends on where the insulation will be installed, as well as the R-value you want to achieve. You can mix types of insulation within an area to add up to a higher R-value. Other factors to consider 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, the higher the R-value the better the climate control and energy efficiency, but it will cost more up front. However, that upfront investment will save money in the long run in the form of more manageable energy and electric bills.
Where is insulation needed in my home?
Areas that generally require insulation include walls, ceilings, and crawlspaces. If your home has a basement and/or attic, you should insulate those as well. Garages, water heaters, and water pipes are often overlooked in home construction, but should still be insulated, though the R-value of each will vary. For example, the attic will have a different R-value than a 2x4 wall or your home’s crawlspace.