The Department of Energy's Federal Energy Policy Act of 1992 required states to certify that their commercial building energy codes meet or exceed the energy conservation requirements of ASHRAE/IESNA 90.1-1989, an energy standard promulgated by ASHRAE, the American Society of Heating, Refrigerating, and Air- Conditioning Engineers. This act also required states' residential building energy codes to meet or exceed the energy conservation requirements of CABO's Model Energy Code.

DOE conducts ongoing review of subsequent versions of these and other energy codes to determine whether these might be the basis for a better national energy policy. In 2002, for commercial construction DOE updated the Federal Energy Policy Act to recognize a later version of the ASHRAE energy standard, ASHRAE/IESNA 90.1-1999. DOE is also currently reviewing another ASHRAE energy standard, ANSI/ASHRAE/IESNA 90.1 2001. For energy conservation in residential construction, DOE now recognizes the ICC's International Energy Conservation Code (IECC), 2003 Edition.

Most State energy conservation codes are currently being updated to reflect DOE recognition of these more recent ASHRAE and ICC energy standards and to maintain compliance with the Federal Energy Policy Act.

Insulation R-values required by these standards are given on the following four pages.

A. ASHRAE/IESNA 90.1-1989, Energy Efficient Design of New Buildings Except Low Rise Residential Buildings

This widely accepted National Voluntary Consensus Standard was developed under the auspices of ASHRAE, the American Society of Heating, Refrigerating, and Air-Conditioning Engineers; it was co-sponsored by the Illuminating Engineering Society of North America. This standard includes energy-efficient design requirements for HVAC systems and equipment intended to improve utilization of energy in buildings. It provides minimum required thermal resistance (R) values for air ducts, plenums, and enclosures based on the temperature differential (TD) at design conditions between the space within which the duct is located and the design air temperature in the duct. The table below shows these required minimum R-values related to duct insulation thickness.

As required by the Energy Policy Act of 1992, each State must certify that its commercial building code energy provisions meet or exceed the requirements of this ASHRAE Standard. Some states have their own energy codes and/or amendments to these codes which provide greater R-values.

(a) Insulation R-values shown are for the insulation as installed and do not include film resistance. The required minimum thicknesses do not consider water vapor transmission and condensation. Additional insulation, vapor retarders, or both, may be required to limit vapor transmission and condensation. For ducts which are designed to convey both heated and cooled air, duct insulation shall be as required by the
most restrictive condition. Where exterior walls are used as plenum walls, wall insulation shall be as required by the most restrictive condition of this section or Section 8 of ASHRAE/IESNA 90.1-1989.
(b) Cooling ducts are those designed to convey mechanically cooled air or return ducts in such systems.
(c) Heating ducts are those designed to convey mechanically heated air or return ducts in such systems.
(d) Insulation resistance measured on a horizontal plane in accordance with ASTM C 518-85 at a mean temperature of 75˚F (24˚C) at the installed thickness.
(e) TD is defined as the temperature difference at design conditions (see ASHRAE Standard 9.4.1) between the space within which the duct is located and the design air temperature in the duct.
(f) Insulation thermal resistance for run-outs to terminal devices less than 10 feet (3.05m) in length need not exceed R-value of 3.3 (RSI = 0.58).
(g) Unconditioned spaces include crawl spaces and attics.

B. ANSI/ASHRAE/IESNA 90.1-2001, Energy Standard for Buildings Except Low Rise Residential Buildings

This National Voluntary Consensus Standard was developed under the auspices of ASHRAE. It was co- sponsored by both the American National Standards Institute (ANSI) and the Illuminating Engineering Society of North America; it supersedes ASHRAE/IESNA 90.1-1989 and is recognized by DOE as the minimum energy conservation standard in commercial construction. Minimum duct system R-values are keyed to building envelope criteria tables found in Appendix B of the Standard, and to climate zone conditions found in Appendix D. Minimum R-values are given in Tables 6.2.4.2A and 6.2.4.2B below.

(a) Insulation R-values, measured in (hr•ft2•˚F)/Btu, are for the insulation as installed and do not include film resistance. The required minimum thicknesses do not consider water vapor transmission and possible surface condensation. Where exterior walls are used as plenum walls, wall insulation shall be as required by the most restrictive condition of 6.2.4.2 or Section 5 of ANSI/ASHRAE/IES 90.1-2001 Insulation resistance measured on a horizontal plane in accordance with ASTM C518 at a mean temperature of 75˚F at the installed thickness.
(b) Includes crawl spaces, both ventilated and non-ventilated.
(c) Includes return air plenums with or without exposed roofs above.

(a) Insulation R-values, measured in (hr•ft2•˚F)/Btu, are for the insulation as installed and do not include film resistance. The required minimum thicknesses do not consider water vapor transmission and possible surface condensation. Where exterior walls are used as plenum walls, wall insulation shall be as required by the most restrictive condition of 6.2.4.2 or Section 5 of ANSI/ASHRAE/IES 90.1-2001. Insulation resistance measured on a horizontal plane in accordance with ASTM C518 at a mean temperature of 75˚F at the installed thickness.
(b) Includes crawl spaces, both ventilated and non-ventilated.
(c) Includes return air plenums with or without exposed roofs above.