ASHRAE-90.1-2022- - Page 253
Extracted Content
A4. BELOW-GRADE WALLS
A4.1 General. For the purpose of Section A1.2, the base assembly is 8 in. medium-weight concrete block with a density of 115 lb/ft [3] and solid grouted cores. Continuous insulation is installed on the interior or exterior. In contrast to the U-factor for above-grade walls, the C-factor for below-grade walls does not include R-values for exterior or interior air films or for soil. For insulated walls, the C-factor does include R-0.45 for 0.5 in. gypsum board.
A4.2 C-Factors for Below-Grade Walls
A4.2.1 C-factors for below-grade walls shall be taken from Table A4.2.1 or determined by the procedure described in this subsection.
A4.2.2 It is acceptable to use the C-factors in Table A4.2.1 for all below-grade walls . A4.2.3 If not taken from Table A4.2.1, below-grade wall C-factors shall be determined from Table A3.1-3, A3.1-2, or A3.1-4 using the following procedure:
a. If the below-grade wall is uninsulated or only the cells are insulated:
-
For concrete walls, determine the C-factor from Table A3.1-2 based on the concrete density and wall thickness.
-
For concrete block walls, determine the C-factor from Table A3.1-3 based on the block size, concrete density, degree of grouting in the cells, and whether the cells are insulated. b. If the mass wall has additional insulation:
-
For concrete walls, determine the Rc from Table A3.1-2 based on the concrete density and wall thickness. Next, determine the effective R-value for the insulation/framing layer from Table A3.1-3 based on the rated R-value of insulation installed, the thickness of the insulation, and whether it is installed between wood or metal framing or with no framing. Then determine the C-factor by adding the Rc and the effective R-value together and taking the inverse of the total.
-
For concrete block walls, determine the Rc from Table A3.1-3 based on the block size, concrete density, degree of grouting in the cells, and whether the cells are insulated. Next, determine the effective R-value for the insulation/framing layer from Table A3.1-4 based on the rated R-value of insulation installed, the thickness of the insulation, and whether it is installed between wood or metal framing or with no framing. Then determine the C-factor by adding the Rc and the effective R-value together and taking the inverse of the total.
A5. FLOORS
A5.1 General. The buffering effect of crawlspaces or parking garages shall not be included in U-factor calculations. See Section A6 for slab-on-grade floors .
A5.2 Mass Floors
A5.2.1 General. For the purpose of Section A1.2, the base assembly is continuous insulation over or under a solid concrete floor . The U-factors include R-0.92 for interior air film, heat flow down; R-1.23 for carpet and rubber pad; R-0.50 for 8 in. concrete; and R-0.46 for semiexterior air film. Added insulation is continuous and uninterrupted by framing. Framing factor is zero.
A5.2.2 Rated R-Value of Insulation for Mass Floors
A5.2.2.1 The rated R-value of insulation is for continuous insulation uninterrupted by framing. A5.2.2.2 Where framing, including metal and wood joists, is used, compliance shall be based on the maximum assembly U-factor rather than the minimum rated R-value of insulation .
A5.2.2.3 For waffle-slab floors, the floor shall be insulated either on the interior above the slab or on all exposed surfaces of the waffle.
A5.2.2.4 For floors with beams that extend below the floor slab, the floor shall be insulated either on the interior above the slab or on the exposed floor and all exposed surfaces of the beams that extend 24 in. and less below the exposed floor .
A5.2.3 U-Factors for Mass Floors
A5.2.3.1 The U-factors for mass walls shall be taken from Table A5.2.3.1. A5.2.3.2 It is not acceptable to use the U-factors in Table A5.2.3.1 if the insulation is not continuous.
A5.3 Steel-Joist Floors
A5.3.1 General. For the purpose of Section A1.2, the base assembly is a floor where the insulation is either placed between the steel joists or is sprayed on the underside of the floor and the joists. In both cases, the steel
ANSI/ASHRAE/IES Standard 90.1-2022 (I-P) 251