ASHRAE Journal - May 2023 - 46

TECHNICAL FEATURE
insulation or even an assembly by a Standard 90.1 user.
Generally, Standard 90.1 provisions treat structure,
cladding, insulation and building materials separately
with different requirements for each. Not all requirements
apply uniformly to IMPs, depending upon how
they are used. This results in multiple potential compliance
paths, each with a possibly different determination.
Addendum cg clarifies this by providing a clear
path of compliance, making Standard 90.1-2022 easier
for users and building officials to apply.
The specific additions to the language are as follows:
* Section 3 defines an insulated metal panel as " a
factory-manufactured panel consisting of metal facings,
an insulative core and a panel joint intended for use in
an assembly forming an exterior wall, an exterior wall
covering or a roof covering of a building envelope. "
* Section 5 adds new sections for IMPs on roofs
(5.5.3.1.5), walls (5.5.3.2.3), ceilings (5.5.3.4.2), which
each clarify that the maximum U-factors of assemblies
that use IMPs are determined by the class of construction
to which the IMP attaches.
* Appendix A adds Section A9.4.7, which states " Ufactors
of insulated metal panels shall be determined
by two- or three-dimensional finite difference or finite
volume computer models or by testing in accordance
with Section A9.3.2 and shall include panel side joints. "
These additions work together to provide a clear path
of compliance for designers and authorities having jurisdiction
(AHJs) when employing these assemblies and
during compliance verification.
Cold-Formed Steel Walls Compliance Calculations
Normative Appendix A, Section A3.3 entitled Steel
Framed Walls, was modified to allow two methods of
determining compliance with the Section 5 Building
Envelope U-factor requirements. The first method uses
Table A3.3.3.1, which contains a listing of precalculated
cold-formed steel walls and the associated U-factors
based on different R-values of continuous insulation.
Note that this method is limited to steel walls with a
framing depth of 3.5 in. or 6 in. (90 mm or 152 mm),
spacing of 16 in. or 25 in. (406 mm or 610 mm) and
thickness up to 54 mils (0.0538 in./1.37 mm).
The new second method uses ANSI/AISI S250-21, North
American Standard for Thermal Transmittance of Building
Envelope With Cold-Formed Steel Framing, 2021 Edition,
for determining compliance with Section 5 Building
46
ASHRAE JOURNAL ashrae.o rg M AY 2023
Envelope requirements. This standard provides an
opportunity for the user to calculate the U-factor for
cold-formed steel framed wall assemblies using framing
spacing from 6 in. to 24 in. (152 mm to 610 mm) oncenter,
framing members depths from 3.5 in. to 12 in.
(90 mm to 305 mm) wide, framing thicknesses from
33 Mils to 64 Mils (e.g., 0.033 in. to 0.064 in. [0.839 mm
to 1.63 mm] thick base metal thickness), as well as insulations
located in the cavity only, in the cavity and outside
the cavity and when outside of the cavity only.
The new option allows the user greater flexibility
to experiment with or choose multiple variations of
a building envelope design using cold-formed steel
framing, which the original Table A3.3.3.1 did not
cover. This method also allows the design professional
or owner to avoid having to submit a costly and timeconsuming
alternative means and method request to a
jurisdiction for approval to use something other than
what is currently listed in Table A3.3.3.1 to demonstrate
compliance.
Wall Solar Reflectance
Several changes were made to the wall solar reflectance
requirements. The first is the removal of " reflectance "
as a defined term within the standard. The
Envelope subcommittee agreed that the previous definition
for reflectance was inaccurate and that there is no
question about what the term reflectance means. In an
effort to simplify the standard, it was decided to remove
the definition rather than amend it. The second change
was to remove the use of solar reflectance index (SRI) for
walls and replace it with the more accurate and relevant
term-solar reflectance. (SRI is still used when referring
to roofs.) Finally, new requirements were added for
south-, east- and west-facing walls to have a minimum
solar reflectance of 0.30 in Climate Zone 0.
For solar reflectance, three options have been provided
for measurement: (a) ASTM C1549, (b) ASTM E903 or (c)
the " G197GT90 " output of the Surface Optics 410-Solar-i
Hemispherical Reflectometer. For emittance, ASTM
C1371 was the simplest and least expensive measurement
method, but other options have been provided.
Initial reflectance was specified because there isn't a fully
developed measurement technique for measuring aged
wall reflectance. Preliminary testing shows that walls get
much less dirty than roofs because they are vertical surfaces.
Finally, planted material as a shading option has
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