ASHRAE-90.1-2022- - Page 238

Extracted Content

A3.2.2.3 Single-Layer in Cavity. The insulation is installed in the cavity between the girts, not compressed by the framing. A membrane or facing, installed separately or adhered to the insulation, is installed inside of the girts to form a continuous layer. A thermal spacer block or thermal break strip between the girts and metal wall panels is required when specified in Table A3.2.3.

A3.2.2.4 Double-Layer. The first rated R-value of insulation is for insulation installed in the cavity between the girts, not compressed by the framing. The second rated R-value of insulation is for insulation compressed between metal wall panels and the steel structure. A membrane or facing, installed separately or adhered to the insulation, is installed inside of the girts to form a continuous layer. A thermal spacer block or thermal break strip between the girts and metal wall panels is required when specified in Table A3.2.3.

A3.2.3 U-Factors for Metal Building Walls. U-factors for metal building walls shall be taken from Table A3.2.3 or determined in accordance with Section A9.2, provided the average girt spacing is at least 52 in. U-factors for metal building wall assemblies with average girt spacing less than 52 in. shall be determined in accordance with Section A9.2.

STANDARD U-VALUES FOR TYPICAL MATERIALS

A3.3.1 General. For the purpose of Section A1.2, the base assembly is a wall where the insulation is installed within the cavity of the cold-formed steel stud framing. The steel stud framing thickness is up to 54

using the values in Table A9.2-2. Additional assemblies include continuous insulation uncompressed and uninterrupted by framing.

A3.3.2 Rated R-Value of Insulation for Steel-Framed Walls

A3.3.2.1 Steel stud framing spaced at 16 in. on-center with cavities filled with 16 in. wide insulation for both 3.5 in. deep and 6.0 in. deep wall cavities serve as the basis for the R-value compliance values in Tables 5.5-0 through 5.5-8.

A3.3.2.2 The first rated R-value of insulation is for uncompressed insulation installed in the cavity between steel studs. It is acceptable for this insulation to also be continuous insulation uninterrupted by framing.

A3.3.2.3 If there are two values, the second rated R-value of insulation is for continuous insulation uninterrupted by framing, etc., to be installed in addition to the first insulation.

A3.3.2.4 Opaque mullions in spandrel glass shall be covered with insulation complying with the steel- framed wall requirements.

A3.3.3 U-Factors for Steel-Framed Walls

A3.3.3.1 U-factors for steel-framed walls shall be determined from one of the following methods:

a. Table A3.3.3.1 b. Testing or calculation methods listed in Section A9.2(b)(3)

A3.3.3.2 Where steel-framed wall framing is spaced greater than 24 in. on center, the U-factor shall be permitted to be determined based on the 24 in. on-center spacing options from Section A3.3.3.1 or based on ASTM C1363 testing at the actual frame spacing used.

A3.3.3.3 Where steel framed wall assemblies contain no cavity insulation, and where the building enve- lope assembly uses continuous insulation to satisfy the minimum R-value for the relevant climate zone in Tables 5.5-0 through 5.5-8, the on-center framing spacing is permitted to be at any dimension.

A3.4 Wood-Framed Walls

A3.4.1 General. For the purpose of Section A1.2, the base assembly is a wall where the insulation is installed between 2 in. nominal wood framing. Cavity insulation is full depth, but values are taken from Table A9.4.3 for R-19 insulation, which is compressed when installed in a 5.5 in. cavity. Headers are double 2 in. nominal wood framing. The U-factors include R-0.17 for exterior air film, R-0.08 for stucco, R-0.56 for 0.625 in. gypsum board on the exterior, R-0.56 for 0.625 in. gypsum board on the interior, and R-0.68 for interior air film, vertical surfaces. Additional assemblies include continuous insulation uncompressed and uninterrupted by framing. U-factors are provided for the following configurations:

a. Standard framing: Wood framing at 16 in. on center with cavities filled w ith 14.5 in. wide insulation for

both 3.5 in. deep and 5.5 in. deep wall cavities. Double headers leave no cavity. Weighting factors are 75% insulated cavity, 21% studs, plates, and sills, and 4% headers.

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