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Corrected U-Factors

ASHRAE Press Release - Feb. 2010

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  • Thermal Design News Release
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ASHRAE Acknowledges Metal Building U-Factors in 90.1 Standard do not reflect typical installations.

On January 12, 2010, the American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) published a news release acknowledging that the thermal performance representations in the 90.1-1999 through 90.1-2010 Standards for typical over-the-purlin, over-the-girt and sag-and-bag methods of insulating pre-engineered metal building roofs and walls do not reflect the performance of these assemblies as they are typically installed.

The news release includes revised thermal performance representations that reflect typical installation practices that were proposed for inclusion in the 90.1-2010 Standard. These representations are found in 90.1 Appendix A.

Industry Investigation

The revised ASHRAE 90.1 Appendix A resulted from a 90.1 Envelope Subcommittee Metal Building Task Group investigation of existing metal building stock that revealed that typical installation practices of the single and double-layer assemblies described in Appendix A compress insulation and thereby negatively affects the thermal performance of the assembly. Published performance values were overstated up to 42%.

See the difference

In addition to the revised values, the news release also included a 'new' metal building roof insulation assembly called a Liner System. Although, liner systems have been on the market for more than 25 years, ASHRAE and now the IECC have finally recognized and incorporated these systems in the energy code.

Liner System (Ls):  A continuous membrane is installed below the purlins and uninterrupted by framing members. Uncompressed, unfaced insulation rests on top of the membrane between the purlins. For multilayer installations, the last rated R-value of insulation is for unfaced insulation draped over purlins and then compressed when the metal roof panels are attached.” - ASHRAE News Release - January 12. 2010


Industry Published Inflated U-Factors

During the investigation on existing buildings, representatives from various companies and organizations in the metal building industry objected to any revisions of these U-Factors, claiming that the U-Factors were correct but that the products were not being installed properly.

Thermal Design vigorously and successfully defended the contractors and erectors that were being blamed for what was clearly a problem with the inflated U-Factors published and defended by these same industry representatives.

The overstated thermal performance values for metal building roof and walls are embedded and used in developing the following codes and standards:

ASHRAE

ICC

90.1-2010 2009 IECC
90.1-2007 2007 IECC Supplement
90.1-2004 2006 IECC*
90.1-2001 2004 IECC Supplement*
90.1-1999  
* The IECC did not publish and reference metal building U-factors until the release of the 2007 Supplement. While both the 2006 IECC and the 2004 Supplement only lists R-values, it is clear the assemblies and economics were based upon the overstated values previously published in 90.1.


Insulation System and Code Compliance

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Does Your Insulation Assembly
Meet Today's Code Intent?

It is important to realize how the revised metal building insulation values impact previous published editions to the ASHRAE 90.1 Standard and International Energy Conservation Code (IECC) that states are currently enforcing.

► Download our General Compliance Brochure (PDF)

Be aware of these revised U-Factors to ensure that the buildings designed, built, inspected and occuppied  actually comply with the intended minimum thermal performance requirements  of their current energy code. Be aware of these revised U-Factors to ensure that the buildings designed, built, inspected and occuppied actually comply with the intended minimum thermal performance requirements of their current energy code. Be aware of these revised U-Factors to ensure that the buildings designed, built, inspected and occuppied actually comply with the intended minimum thermal performance requirements of their current energy code.

Complying With The Intent Of The Code

Normative Appendix A of the 90.1 Standard, RATED R-VALUE OF INSULATION AND ASSEMBLY U-FACTOR, C-FACTOR, AND F-FACTOR DETERMINATIONS provides pre-calculated assembly U-Factors for metal building insulation assemblies (Metal Building Roofs: A2.3, Metal Building Walls: A3.2).

Section A1.1 identifies these as typical construction assemblies which have been proven to be false and mis-represented. A1.1 states that these values shall be used for all calculations unless otherwise allowed by A1.2. In A1.2, the Standard states that if the building official determines that the proposed construction assembly is not adequately represented in A2 through A8, the applicant shall determine appropriate values for the assembly using the assumptions in A9.

It is clear that the typical proposed metal building insulation assembly is NOT adequately represented in A2 through A8. Therefore, the applicant shall determine appropriate values by other means. Based on this language, applicants must utilize the corrected U-Factors for these assemblies in order to be consistent with the language 90.1 Standard, or provide hot box testing or modeling of a true representative insulation assembly as typically installed.

Complying With Professional Ethics & Integrity

The thermal performance of typical metal building insulation assemblies that you have relied upon are wrong and have been wrong for many years. As a professional knowing this information, you have a duty and an obligation to your trade, your organization, and your environment to do the right thing and stop the energy waste.

Complying With The Owners' Best Interests

Whether you specify, design, build or grant occupancy for the building owner; today's decision is going to impact the owner for the life of the building. Now is the opportunity to guide owners towards intended energy efficiency. After all, these are minimum requirements!

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