ASHRAE-90.1-2022- - Page 231

Extracted Content

(This is a normative appendix and is part of this standard.)

NORMATIVE APPENDIX A RATED R-VALUE OF INSULATION AND ASSEMBLY  U-FACTOR, C-FACTOR, AND F-FACTOR DETERMINATIONS

A1. GENERAL

Where using Normative Appendix A to demonstrate compliance with Section 5.5, the thermal performance of building envelopes shall be determined in accordance with Section A1.1 or A1.2.

A1.1 Precalculated Assembly U-Factors, C-Factors, F-Factors, or Heat Capacities. Precalculated U- factors, C-factors, F-factors, and heat capacities for typical building envelope assemblies shall be used for assemblies consistent with the specifications in Sections A2 through A8. These precalculated values shall be permitted to be used to demonstrate compliance for a building envelope assembly with any type of exterior covering or interior finish.

Interpolation between values in a particular table in Normative Appendix A shall be permitted for rated R-values of insulation, including insulated sheathing. Extrapolation beyond values in a table in Normative Appendix A is not allowed.

A1.2 Applicant-Determined Assembly U-Factors, C-Factors, F-Factors, or Heat Capacities. Testing, calculation, and modeling procedures in Section A9 shall be used to determine U-factors, C-factors, F-factors or heat capacities for assemblies that are not addressed by or are different from the assembly specifications listed in Sections A2 through A8 and the associated precalculated values.

A1.3 Applicant-Determined Psi-Factors and Chi-Factors for Thermal Bridges. The applicant shall determine values for point thermal bridges and linear thermal bridges using the assumptions in Section A10.

A2. ROOFS

A2.1 General. The buffering effect of suspended ceilings or attic spaces shall not be included in U-factor calculations.

A2.2 Roofs with Insulation Entirely Above Deck

A2.2.1 General. For the purpose of Section A1.2, the base assembly is continuous insulation over a structural deck. The U-factor includes R-0.17 for exterior air film, R-0 for metal deck, and R-0.61 for interior air film heat flow up. Added insulation is continuous and uninterrupted by framing. The framing factor is zero.

A2.2.2 Rated R-Value of Insulation. For roofs with insulation entirely above deck, the rated R-value of insulation is for continuous insulation .

Exception to A2.2.2: Interruptions for framing and pads for mechanical equipment are permitted with a

combined total area not exceeding one percent of the total opaque assembly area.

A2.2.3 U-Factor. U-factors for roofs with insulation entirely above deck shall be taken from Table A2.2.3. It is not acceptable to use these U-factors if the insulation is not entirely above deck or not continuous.

A2.3 Metal Building Roofs

A2.3.1 General. For the purpose of Section A1.2, the base assembly is a roof with thermal spacer blocks where the insulation is draped over the steel structure (purlins), spaced nominally 5 ft on center and compressed when the metal roof panels are attached to the steel structure (purlins).

A2.3.2 Rated R-Value of Insulation

A2.3.2.1 Single Layer. The rated R-value of insulation is for insulation installed perpendicular to and draped over purlins and then compressed when the metal roof panels are attached. A minimum R-3 thermal spacer block between the purlins and the metal roof panels is required unless compliance is shown by the overall assembly U-factor .

A2.3.2.2 Double Layer. The first rated R-value of insulation is for insulation installed perpendicular to and draped over purlins. The second rated R-value of insulation is for unfaced insulation installed above the first layer and parallel to the purlins and then compressed when the metal roof panels are attached. A minimum R-3 thermal spacer block between the purlins and the metal roof panels is required unless compliance is shown by the overall assembly U-factor .

A2.3.2.3 Continuous Insulation. For assemblies with continuous insulation the continuous insulation is installed above or below the purlins, uncompressed and uninterrupted by framing members.

A2.3.2.4 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

ANSI/ASHRAE/IES Standard 90.1-2022 (I-P) 229