On its own, R-value doesn’t carry much clout as an effective guide.
If you’ve dealt with insulation, chances are you’re aware of R-value. It refers to insulation’s resistance to heat flow. It measures thermal resistance to heat flow offered by traditional insulation – conductive flow – in a controlled setting. The higher this value is, the greater the insulating power. While it’s an indicator to check and know, it’s not quite the sacrosanct determiner for all things insulation that some may lead you to believe.
On its own, R-value doesn’t carry much clout as an effective guide. Reducing insulation to a single number fails in telling the whole story since in homes, heat also flows in or out through radiation and convection. Heat loss through convection (air leakage) can account for as much as 40% of total energy lost by your home, according to the U.S. Department of Energy. This is a problem when only using R-value. Among the elements and outside of the lab, more dimensions and factors are needed to conclude the right insulation for a home or building.
Let’s use loose-fill fiberglass insulation in an attic as an example. In cold climates, air begins to circulate into and within the insulation, creating convective loops that increase heat loss, thus decreasing R-value. At extremely cold temperatures that R-value could see a 50% decrease.
Another factor affecting R-value includes how your home is built. Whether it’s a single- or multi-level home, the type of ceiling, if there’s a basement, and more all introduce variables to R-value. Additionally, how you heat or cool your home also plays a role in affecting R-value.
So what besides R-value should you know about your insulation options?
Resistance to air penetration and to vapor drive is a good starting point. It’s about determining R-value after the insulating material is subjected to an actual home environment.
Outside of a high R-value, superior insulation is pneumatically or spray applied, fully filling to your home’s cavity. R-value isn’t so much an end-all determiner, but a starting point in delving into the potential effectiveness of the insulation you choose to employ.
Properly insulating your home means knowing some operational features of your home and the environment it sits in. R-value is a component within the equation of finding the right insulation for your home – not the answer itself.
About Eric Garcia
Eric brings his knowledge and training in building science, training in spray and injection foams from the manufacturers, more than 8 years installing foam insulation, as well as selling and managing in the foam insulation industry. He is also BPI and Dale Carnegie certified and has taken several building science courses including air sealing and building envelope. Eric’s responsibilities include overseeing and giving support to all of the branches of the RetroFoam of Michigan company, office, estimates, and installs. He is also the Professor of Foam on our educational YouTube series Foam University. Even when Eric is off he is usually still “working” or thinking about work, but when he can get away he enjoys camping, hiking, hunting, and woodwork.