Understanding the R- and U-Values of Insulation

June 1, 2008

Learn how these standardized rating systems ensure consistency in energy performance

Improved insulation is a good step toward improving building efficiency, particularly since the Atlanta-based American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) increased minimum roof-insulation levels in 2007 in its Standard 90.1—the first increase in 18 years. And, if that isn't enough to spur someone into action: A recent McKinsey & Co. report named insulation as the single most cost-effective way to improve energy efficiency based on cost comparison per square foot.

A standardized insulation rating system ensures consistency, with insulating materials rated in R- and U-values. R-values represent resistance to the flow of heat; the higher the R-value, the greater the resistance and the insulating value. U-values are the direct opposite, representing the amount of heat that escapes through a material. The lower the U-value, the slower the rate of heat flow and the better the insulating quality.

Ultimately selecting which product and value to use depends on many factors - particularly thermal load; regardless, ASHRAE's new above-deck roof insulation standard is a good place to start, as it jumped 33 percent, from R-15 to R-20, in five of six climatic regions. "This standard is not a requirement to retrofit—it's a guideline—but it can become one if a state adopts it as a building code," explains Jeff Harris, vice president for programs at the Alliance to Save Energy, Washington, D.C. "Standards should be considered for new builds and major renovations—any time you have a reasonable opportunity to add insulation, you should."

Still, that doesn't necessarily mean that more insulation is better. Although R-value is proportional to insulation thickness, it also depends on the type of material and its density. The more air pockets in an insulating product, the higher the R-value.

"Glass façades are the perfect example of aesthetics colliding with physics," explains Paul Bertram, director of environment and sustainability for the North American Insulation Manufacturers Association, Alexandria, VA. "You can attain efficiencies, but there are tradeoffs. Regardless of a building's design, the answer isn't stuffing in as much insulation as you can; you'll reach a point of diminishing return. Coordination between all building systems is a leading indicator of energy efficiency, and optimizing that integration can best be achieved when architects and engineers work as a team. Proper installation is also as important as the product you're using."

Rated R-Value and Thickness of Insulation*


 R6   R11 R13 R15 R19 R21  R22 R25 R30 (C**)  R30   R38 (C**) R38 

Insulation Thickness

 1.75"  2.5"  3.5"  3.5"  3.5"  6.25"  5.5"  6.5"  8"  8.5"  10"  10"  12"

* All listed thicknesses are approximate and may vary by +/- 0.5 inches.

** The "C" denotes high-density materials specifically designed for installation in areas where space is limited, such as cathedral ceilings.

Stephanie J. Oppenheimer, former assistant vice president of communications at BOMA Intl., is principal at Skylite Communications, based in Falls Church, VA.

Getting More for Your Insulation Investment
Visit these websites for more information on finding the right insulation for your needs, and for information about tax incentives and rebates.

  • To read about benchmarking, visit the site of the Commercial Buildings Energy Consumption Survey (CBECS), which collects information on U.S. commercial buildings, their energy-related characteristics, and their energy consumption and expenditures.
  • To read about software modeling, visit the site of the Energy-Wise Roof Calculator, an interactive software application with a graphical method for constructing roof assemblies that evaluates thermal efficiency and estimates energy costs.
  • To read about tax incentives, visit the website of the Tax Incentives Assistance Project (TIAP), which provides information about federal income tax incentives for energy-efficient products and technologies. Or, visit the Database of State Incentives for Renewables & Efficiency site, which features information on state, local, utility, and federal incentives that promote renewable energy and energy efficiency.

Voice your opinion!

To join the conversation, and become an exclusive member of Buildings, create an account today!

Sponsored Recommendations

Decarbonization 2024: How Digital Tools Minimize Your Carbon Footprint

Discover the untapped potential of digital electricity infrastructure in revolutionizing building electrification and decarbonization, unlocking a sustainable future while reducing...

Building Security & Technology Series: Webinar 3 - Proptech

Date: May 22, 2024Time: 1:00 PM EDT / 12:00 PM CDT / 10:00 AM PDT / 5:00 PM GMT Duration: 1 Hour eachGold Sponsors: Genetec, ISS, PrometheusSilver Sponsors: Eagle Eye Networks...

Building Security & Technology Series: Webinar 4 - Lessons Learned

Date: May 29, 2024Time: 1:00 PM EDT / 12:00 PM CDT / 10:00 AM PDT / 5:00 PM GMTDuration: 1 Hour eachGold Sponsors: Genetec, ISS, PrometheusSilver Sponsors: Eagle Eye Networks,...