ASHRAE-90.1-2022- - Page 267
Extracted Content
a. ASTM C177 b. ASTM C518 c. ASTM C1363
For concrete, the oven-dried conductivity shall be multiplied by 1.2 to reflect the moisture content as typically installed.
A9.3.2 Assembly U-Factors. If assembly U-factors are determined by testing, ASTM C1363 test procedures shall be used.
Product samples tested shall be production-line material or representative of material as purchased by the consumer or contractor. If the assembly is too large to be tested at one time in its entirety then either a representative portion shall be tested or different portions shall be tested separately and a weighted average determined. To be representative, the portion tested shall include edges of panels, joints with other panels, typical framing percentages, and thermal bridges .
A9.4 Calculation Procedures and Assumptions. The following procedures and assumptions shall be used for all calculations. R-values for air films, air spaces, insulation, and building materials shall be taken from Sections A9.4.1 through A9.4.4, respectively. In addition, applicable assumptions listed in Sections A2 through A8, including framing factors, shall be used.
A9.4.1 Air Films. Prescribed R-values for air films shall be as follows:
R-Value Condition 0.17 All exterior surfaces 0.46 All semiexterior surfaces 0.61 Interior horizontal surfaces, heat flow up 0.92 Interior horizontal surfaces, heat flow down 0.68 Interior vertical surfaces
A9.4.1.1 Exterior surfaces are areas exposed to the wind. A9.4.1.2 Semiexterior surfaces are protected surfaces that face attics, crawlspaces, and parking garages with natural or mechanical ventilation .
A9.4.1.3 Interior surfaces are surfaces within enclosed spaces . A9.4.2 Air Spaces. The R-value for air spaces shall be taken from Table A9.4.2-1 based on the effective emittance of the surfaces facing the air space from Table A9.4.2-2, provided the following criteria are satisfied:
a. The air space shall be an enclosed and unventilated cavity designed to minimize airflow into and out of
the enclosed air space. Airflow shall be deemed minimized when the enclosed air space is located on the interior of the continuous air barrier and bounded on all sides by building components. b. Reflective insulation as defined in ASTM C1224, where used, shall be fitted closely around all non-heat producing components and taped or otherwise sealed to eliminate gaps or voids through which air, dust, or water vapor has the potential to pass. c. Nonparallel spaces shall use the average distance to determine the thickness of the air space. d. Air spaces less than 0.5 in. thickness shall have no R-value . e. The R-value for 3.5 in. air spaces shall be used for air spaces of that thickness or greater, provided that air
space does not exceed 12 in. between the surfaces at any point.
For material emissivity properties not listed in Table A9.4.2-2, Equation A9.4-1 shall be permitted to calculate the effective emissivity for the air space.
1/ eeff = 1/ e 1 + 1/ e 2 – 1 (A9.4-1)
where eeff = effective emittance for the air space e 1 = surface 1 emittance e 2 = surface 2 emittance A9.4.3 Insulation R-Values. Insulation R-values shall be determined as follows:
a. For insulation that is not compressed, the rated R-value of insulation shall be used. b. For calculation purposes, the effective R-value for insulation that is uniformly compressed in confined
cavities shall be taken from Table A9.4.3. c. For calculation purposes, the effective R-value for insulation installed in cavities in attic roofs with steel
joists shall be taken from Table A9.2-1.
ANSI/ASHRAE/IES Standard 90.1-2022 (I-P) 265