Focus On: The ASTM C518, the R-Value Test

March 20, 2024   -  

What Is the R-Value Test?

ASTM C518, or the R-value test, is a test method used to measure the thermal resistance of materials, indicating their effectiveness in preventing heat transfer. It is a crucial metric in the field of insulation, helping assess how well a material can resist the flow of heat. The higher the R-value, the better the insulating properties of the material.

This test is particularly essential in determining the efficiency of insulation products, aiding homeowners, builders, and architects in making informed decisions to enhance energy efficiency and reduce heating and cooling costs.

Conducted under standardized conditions, the R-value test plays a key role in ensuring that insulation materials meet specific performance standards.

How to Test R-Value

R = ΔT / Q

Going hand in hand with thermal resistance is thermal conductance, the time rate of steady-state heat flow through a unit area of a material induced by a unit temperature difference.

Experimentally, to measure the thermal conductance of a material, place a test specimen between two parallel plates at constant but different temperatures and measure the steady-state one-dimensional heat flux through the specimen.

The inverse of thermal conductance is thermal resistance, the ability of a material to resist the flow of heat. In the building and construction industry, R-value is a measure of thermal resistance. Under steady-state conditions, it is the ratio of a temperature difference (ΔT) across a material and the heat flux (Q) flowing through it.

Here at NGC Testing Services, we test in accordance with the most current version of ASTM C518 to determine the R-value of materials utilizing the principles as illustrated.

Working With an Accredited Lab for R-Value Testing

Any laboratory you utilize for analytical testing should be accredited. Be sure to check a lab’s scope of accreditation by looking under its lab code for that accreditation or listing.

Gaining and maintaining accreditations requires a significant amount of effort, which includes establishing a comprehensive quality system, collection of data, and periodic in-depth, on-site assessments. At NGC Testing Services, our industry-preferred accreditations underscore our pride in delivering top-notch testing services. Accreditations include:

National Voluntary Laboratory Accreditation Program (NVLAP)

Lab Code: 200291-0

NVLAP is administered by the National Institute of Standards and Technology (NIST), part of the U.S. Department of Commerce.

International Accreditation Service (IAS)

Testing Laboratory 216

IAS is a subsidiary of the International Code Council (ICC).

City of New York, MEA

Acceptance Laboratory — No. 102-01-L

California State Fire Marshal (OSFM)

Approved Testing Laboratory

Florida Building Commission

Approved Product Testing Laboratory

UL's Third Party Test Data Program (TPTDP)

Acoustical Testing — File DA1294

ISO/IEC 17025 Compliant

This is the basic requirement utilized by most laboratory accreditation organizations. Issued by the International Organization for Standardization (ISO) and the International Electrotechnical Commission (IEC), it is the single most important standard for calibration and testing laboratories around the world.

Laboratories that are accredited to this international standard have demonstrated that they are technically competent and able to produce precise and accurate test and/or calibration data.

Mutual Recognition Arrangements

In addition, there are Mutual Recognition Arrangements (MRA) among accreditation bodies around the world that include NVLAP and IAS, our primary accreditations. Our two MRAs are the Asia Pacific Laboratory Accreditation Cooperation (APLAC) and the International Laboratory Accreditation Cooperation (ILAC).

The Final Word on R-Value Testing

The R-value test stands as a pivotal tool in our journey toward well-insulated and energy-efficient living space.

By understanding thermal resistance, we empower ourselves to make informed decisions about insulation materials and methods. The significance of this test echoes not just in its technical precision but in its tangible impact on our homes, our comfort, and our energy bills.

Need a reliable assessment of the thermal resistance of your building material or assembly? Reach out to the dedicated team at NGC Testing Services to get started today.

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This post was originally published in September 2021 by Bob Menchetti and was updated and republished in March 2024.


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