ASHRAE-90.1-2022- - Page 254
Extracted Content
provides a thermal bypass to the insulation. The U-factors include R-0.92 for interior air film, heat flow down; R-1.23 for carpet and pad; R-0.25 for 4 in. concrete; R-0 for metal deck; and R-0.46 for semiexterior air film. The performance of the insulation/framing layer is calculated using the values in Table A9.2-1.
A5.3.2 Rated R-Value of Insulation for Steel-Joist Floors
A5.3.2.1 The first rated R-value of insulation is for uncompressed insulation installed in the cavity between steel joists or for spray-on insulation.
A5.3.2.2 It is acceptable for this insulation to also be continuous insulation uninterrupted by framing. All continuous insulation shall be installed either on the interior above the floor structure or below a framing cavity completely filled with insulation.
A5.3.3 U-Factors for Steel-Joist Floors
A5.3.3.1 The U-factors for steel-joist floors shall be taken from Table A5.3.3.1. A5.3.3.2 It is acceptable to use these U-factors for any steel-joist floor .
A5.4 Wood-Framed and Other Floors
A5.4.1 General. For the purpose of Section A1.2, the base assembly is a floor attached directly to the top of the wood joist with insulation located directly below the floor and ventilated air space below the insulation. The heat flow path through the joist is calculated to be the same depth as the insulation. The U-factors include R-0.92 for interior air film, heat flow down; R-1.23 for carpet and pad; R-0.94 for 0.75 in. wood subfloor; and R-0.46 for semiexterior air film. The weighting factors are 91% insulated cavity and 9% framing.
A5.4.2 Rated R-Value of Insulation for Wood-Framed and Other Floors. The first rated R-value of insulation is for uncompressed insulation installed in the cavity between wood joists.
A5.4.2.1 It is acceptable for this insulation to also be continuous insulation uninterrupted by framing. All continuous insulation shall be installed either on the interior above the floor structure or below a framing cavity completely filled with insulation.
A5.4.3 U-Factors for Wood-Framed Floors
A5.4.3.1 The U-factors for wood-framed floors shall be taken from Table A5.4.3.1. A5.4.3.2 It is not acceptable to use these U-factors if the framing is not wood.
A6. SLAB-ON-GRADE FLOORS
A6.1 General. For the purpose of Section A1.2, the base assembly is a slab-on-grade floor of 6 in. concrete poured directly on to the earth, the bottom of the slab is at grade line, and soil conductivity is 0.75 Btu/h·ft·°F. In contrast to the U-factor for floors, the F-factor for slab-on-grade floors is expressed per linear foot of building perimeter. F-factors are provided for unheated slabs and for heated slabs. Unheated slab-on-grade floors do not have heating elements, and heated slab-on-grade floors do have heating elements within or beneath the slab. F-factors are provided for five insulation configurations:
a. Horizontal Insulation: Continuous insulation is applied directly to the underside of the slab and extends
inward horizontally from the perimeter for the distance specified, or continuous insulation is applied downward from the top of the slab and then extends horizontally to the interior or the exterior from the perimeter for the distance specified. b. Vertical Insulation: Continuous insulation is applied directly to the slab exterior, extending downward
from the top of the slab for the distance specified. c. Fully Insulated Slab: Continuous insulation extends downward from the top of the slab and along the
entire perimeter and completely covers the entire area under the slab. d. Under-Slab Insulation only: Insulation installed under the entire slab. The slab edge remains uninsulated. e. Uninsulated: Slabs without insulation under the slab and at the slab edge.
A6.2 Rated R-Value of Insulation for Slab-on-Grade Floors
A6.2.1 The rated R-value of insulation shall be installed around the perimeter of the slab-on-grade floor to the distance specified.
Exception to A6.2.1: For a monolithic slab-on-grade floor, the insulation shall extend from the top of the
slab-on- grade to the bottom of the footing.
A6.2.2 Insulation installed inside the foundation wall shall extend downward from the top of the slab a minimum of the distance specified or to the top of the footing, whichever is less.
A6.2.3 Insulation installed outside the foundation wall shall extend from the top of the slab or downward to at least the bottom of the slab and then horizontally to a minimum of the distance specified. In all cli
252 ANSI/ASHRAE/IES Standard 90.1-2022 (I-P)