Enercept Explains: What is R-Value?

Posted by Greg Archer on September 26, 2019

When we talk about Structural Insulated Panels (SIP), the term R-value inevitably enters the conversation. A wall is R-19, a roof is R-30 – what does this mean?

Enercept Explains LogoR-value measures the ability of insulation material to resist heat transfer. The R-value is a very accurate and reliable expression of how insulation materials perform with regard to conduction of energy. With heating and cooling accounting for 50 percent of energy use in the average home, the type of insulation you choose can save thousands of dollars in utility bills over the life of your home.

R-value is a laboratory measurement that measures conduction, but it does not effectively measure the other two methods of heat transfer: convection and radiation. However, R-value is only telling one-third of the story of how well your home will be insulated in real world conditions.  R-value is important, but building scientists know that focusing on R-value to the exclusion of all other factors can result in disappointment. It’s known, for instance, that thermal bridging can reduce the actual energy efficiency of a wall by up to 50 percent. U.S. scientists have proven that convective flows — like those found in some very light density attic insulation — can reduce its performance by more than 40 percent under winter conditions.

Most manufacturers list the individual R-value of their insulation products. This R-value represents the R-value of that piece at the time of installation under ideal conditions. For instance, if you purchase a roll of R-19 fiberglass insulation, that number refers to the best possible R-value offered by that roll of insulation. However, once the batt is installed, the value starts to go down immediately.

Here at Enercept, we often tell people SIPs provide a lifetime of energy savings. Here’s why: Once a SIP structure is complete, the effective R-value will remain constant over time. This is not the case with other insulation products. The R-value of a wall diminishes when batting falls over time due to gravity. Spray foams that use a thermal resistant material as its blowing agent will off-gas that agent, losing much of that added insulating value, within five years.

RValue 3But R-value does not tell the whole story. Lab tests that determine R-value have little resemblance to how insulation actually performs in a home. When real world factors such as air infiltration, extreme temperatures and thermal bridging are present, field-installed fiberglass insulation can lose more than half its R-value. Research has repeatedly shown that SIPs provide continuous insulation that will maintain its stated R-value for the life of the home and outperform fiberglass insulation every time.

The effort to maintain a constant and comfortable temperature inside your home is hampered by two forces: conduction and convection. Conduction is the transfer of heat through a solid material, which is what insulation is designed to prevent. Convection is the transfer of air through gaps in the walls and roof of the home. Outside air leaking into the home, or air infiltration, is responsible for 40 percent of heat or cooling loss in the average home.

Thermal Bridging

Fiberglass insulation does not protect against air infiltration, as shown in a comparative test conducted by Oak Ridge National Laboratories. Researchers built two identical 2,600 sq. ft. homes, one made of SIPs and one with conventional wood framing and fiberglass insulation. The SIP research home was five times more airtight than the wood-frame room when measured by a blower door test. SIPs not only serve as a framing and insulation material, but also as a code compliant air barrier. SIP homes have routinely tested two to three times more airtight than wood frame homes with fiberglass insulation.

The most important factor in thermal efficiency is the continuity of the insulation. The Enercept SIPs system provides a solid envelope of continuous insulation. The Enercept system has the ability to resist heat transfer by both conduction and convection. By a comparison conducted by Oak Ridge National Laboratory study, a conventional stick-built home would require a R-40 wall to compete with a 6-inch Enercept wall which has an R-value of 24.

Air infiltration can also cause more problems than just higher utility bills. Air that passes through fiberglass insulation often carries moisture. This can cause unseen mold growth in wall cavities and overall poor indoor air quality that can lead to health problems for occupants. Enercept SIPs addresses those principles by providing more R-value, less air leakage and less thermal bridging than other construction methods offering a lifetime benefit of energy savings.

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Our Mission: Our Commitment
When you build with Enercept SIPs we provide a building that will go up faster and will be warmer, tighter, stronger, quieter and more cost-effective than conventional construction. It is a commitment that others simply can’t beat!

Topics: Energy Efficiency, SIPs, r-value, insulation, Green Building