Code Changes Affecting the Building Enclosure in the 2024 International Building Code

system that incorporates photovoltaic modules
and functions as a component an integral
part of the building envelope, such as roof
assemblies and roof coverings, exterior wall
envelopes and exterior wall coverings, and
fenestration.”
New definitions for ground-mounted and
elevated photovoltaic support structures were
added:
• “PHOTOVOLTAIC (PV) PANEL SYSTEM,
GROUND MOUNTED. An independent
photovoltaic (PV) panel system without usable
space underneath, installed directly on the
ground.”
• “PHOTOVOLTAIC (PV) SUPPORT STRUCTURE,
ELEVATED. An independent photovoltaic (PV)
panel support structure designed with usable
space underneath with minimum clear height
of 7 feet 6 inches (2286 mm), intended for
secondary use such as providing shade or
parking of motor vehicles.”
A new definition of low-slope was added to
clarify that it applies to “a roof slope less than 2
units vertical in 12 units horizontal (17-percent
slope).” Taken with the existing definition of
steep-slope, this clarifies that a roof with an exact
slope of 2:12 is not low slope with regard to code
requirements.
Three other interrelated definitions pertaining
to roofs were added or revised, including
those for landscaped roof, occupiable roof, and
vegetative roof. Numerous instances throughout
the 2024 IBC have been modified related to
these three types of roofs.
Two new definitions state:
• “LANDSCAPED ROOF. An area over a roof
assembly incorporating planters, vegetation,
hardscaping or other similar decorative
appurtenances that are not part of the roof
assembly.”
• “OCCUPIABLE ROOF. An exterior space on a
roof that is designed for human occupancy,
other than maintenance or repair, and is
Feature
Code Changes Affecting the
Building Enclosure in the 2024
International Building Code
By Emily Lorenz, PE, F-ACI
Interface articles may cite trade, brand,
or product names to specify or describe
adequately materials, experimental
procedures, and/or equipment. In no
case does such identification imply
recommendation or endorsement by the
International Institute of Building Enclosure
Consultants (IIBEC).
equipped with a means of egress system
meeting the requirements of this code.”
The revised vegetative roof definition now
reads: “VEGETATIVE ROOF. An A roof assembly
of interacting components designed to
waterproof a building’s top surface that includes,
by design, vegetation and related landscape
elements a vegetative surface.”
A final new definition related to roofs
was added in “RAISED-DECK SYSTEM. (For
application to Chapter 15 only). A system
consisting of decking or pavers supported by
pedestals installed over a roof assembly to
provide a walking surface.”
Related to walls, two definitions were revised.
The term exterior wall envelope was changed
to exterior wall assembly and is now defined as
“a system or assembly of including the exterior
wall covering, framing, and components,
including exterior wall covering materials, that
such as weather-resistive barriers and insulating
materials. This system provides protection of the
building structural members, including framing
and sheathing materials, and conditioned
interior space, from the detrimental effects of
the exterior environment.” The definition of
exterior wall covering was modified to include
rainscreen systems.
New definitions related to walls or roofs
include:
• “INSULATED METAL PANEL (IMP). A factory
manufactured panel consisting of metal
facings and an insulation core intended for
EVERY THREE YEARS, the model codes
developed by the International Code Council
(ICC) are updated through an open, transparent
process. The most recent ICC codes (known as
International Codes or I-codes) were published
in 2024 and are available for adoption by
jurisdictions. Jurisdictions adopt model
codes on various schedules through unique
processes; IIBEC members should consult their
state or local jurisdictions to determine when
the 2024 codes may be adopted.
This article will focus on significant changes to
the 2024 model code, the International Building
Code (IBC),1 from the 2021 edition. Not all
changes included in the 2024 edition of the IBC
model code that may impact building enclosure
projects are included in this article.
CHAPTER 2: DEFINITIONS
A new definition of basic wind speed and the
revision of the definition of wind speed are
due to changes in the base standard ASCE
7-22,2 which was adopted as part of the 2024
IBC. The new definition states: “BASIC WIND
SPEED, V. The wind speed used for design, as
determined in Chapter 16,”1 where V is the
variable used to denote basic wind speed. A
detailed discussion of the changes related to
calculation of wind loads is available in Mehta
and Patterson’s publication, Wind Uplift
Pressures on Low-Slope Roofs,3 and in Scott’s
“Effects of ASCE 7-22 Wind Load Provisions on
Roof Covering Design.”4
Several definitions were added related to
building-integrated photovoltaics (BIPV). A
new definition of BIPV roof covering was added:
“BUILDING-INTEGRATED PHOTOVOLTAIC
(BIPV) ROOF COVERING. A BIPV system that also
functions as a roof covering. Coverings include, but
are not limited to, shingles, tiles and roof panels.”
The 2021 IBC term BIPV product was revised
to be BIPV system as such: “A building product
©2024 International Institute of Building Enclosure C July/August 2024 onsultants (IIBEC) IIBEC Interface • 29
use as a system forming an exterior wall, an
exterior wall covering, a roof covering or a roof
assembly of a building.”
• “INSULATED VINYL SIDING. A continuous
insulation cladding product, with
manufacturer-installed foam plastic insulating
material as an integral part of the cladding
product, having a thermal resistance not less
than R-2.”
• “METAL BUILDING SYSTEM. An integrated set
of fabricated components and assemblies that
form a complete or partial building shell that
is designed by the manufacturer. This system
typically includes but is not limited to primary
framing composed of built-up structural
steel members, secondary members that are
cold-formed steel or open-web steel joists,
a metal panel roof system and exterior wall
cladding. The system is manufactured in a
manner that permits plant or field inspection
prior to assembly or erection.”
• “RAINSCREEN SYSTEM. An assembly applied
to the exterior side of an exterior wall and
consisting of, at minimum, an outer layer,
an inner layer and a cavity between them
sufficient for the passive removal of liquid
water and water vapor.”
• “RESPONSIVE VAPOR RETARDER. A vapor
retarder material complying with a vapor
retarder class of Class I or II, but that also has
a vapor permeance of 1 perm or greater in
accordance with ASTM E96, water method
(Procedure B).”
CHAPTER 7: FIRE AND SMOKE
PROTECTION FEATURES
New requirements in Chapter 7 have been added
to reduce the likelihood of fire spreading. The
new Section 705.6 states:
“705.6 Continuity. The fire-resistance rating
of exterior walls shall extend from the top of the
foundation or floor/ceiling assembly below to
one of the following:
1. The underside of the floor sheathing, roof
sheathing, deck or slab above.
2. The underside of a floor/ceiling or roof/
ceiling assembly having a fire-resistance
rating equal to or greater than the exterior
wall and the fire separation distance is
greater than 10 feet.
Parapets shall be provided as required by
Section 705.12.”
A new Section 705.7.1 has been added under
Section 705.7, Structural Stability, that reads:
“705.7.1 Floor assemblies in Type III
construction. In Type III construction where
a floor assembly supports gravity loads from
an exterior wall, the fire-resistance rating of the
portion of the floor assembly that supports
the exterior wall shall be not less than the fireresistance
rating required for the exterior wall in
Table 601. The fire-resistance rating provided
by the portion of the floor assembly supporting
and within the plane of the exterior wall shall
be permitted to include the contribution of the
ceiling membrane when considering exposure
to fire from the inside. Where a floor assembly
supports gravity loads from an exterior wall,
the building elements of the floor construction
within the plane of the exterior wall, including
but not limited to rim joists, rim boards and
blocking, shall be in accordance with the
requirements for interior building elements of
Type III construction.”
In Section 715, Joints and Voids, three
exceptions have been added to both
Section 715.4, Exterior Curtain Wall/
Fire-Resistance-Rated Floor Intersections,
and Section 715.5, Exterior Curtain Wall/
Nonfire-Resistance-Rated Floor Assembly
Intersections. In Section 715.4 it states:
“Exceptions: An approved perimeter fire
containment system shall not be required for
voids in the following locations:
1. Floors within a single dwelling unit.
2. Floors and ramps within parking garages or
structures constructed in accordance with
Sections 406.5 and 406.6.
3. Mezzanine floors.”
Exceptions for Section 715.5 reads:
“Exceptions: An approved material or
system to retard the interior spread of fire and
hot gases shall not be required for voids in the
following locations:
1. Floors within a single dwelling unit.
2. Floors and ramps within parking garages or
structures constructed in accordance with
Sections 406.5 and 406.6.
3. Mezzanine floors.”
Additionally, a new section was added for
roof assembly intersections in Section 715.6,
which states:
“715.6 Fire barrier/nonfire-resistance-rated
roof assembly intersections. Voids created
at the intersection of a fire barrier and the
underside of a nonfire-resistance-rated roof
sheathing, slab or deck above shall be filled
by an approved material or system to retard
the passage of fire and hot gases, or shall be
protected by an approved continuity head-of-wall
system tested in accordance with ASTM E2837
to provide an F rating/T rating for a time period
not less than the required fire-resistance rating of
the fire barrier in which it is installed.”
CHAPTER 14: EXTERIOR WALLS
With the change in the definition section
of exterior wall envelope to exterior wall
assembly, many changes in Chapter 14 relate
to terminology changes. However, several
significant changes have been made related to
fire and flame propagation.
New Sections 1402.5, 1402.7, and 1402.8
related to vertical and lateral flame propagation
have been added. Section 1402.5 states:
“1402.5 Vertical and lateral flame
propagation. Exterior walls on buildings
of Type I, II, III and IV construction that
contain a combustible exterior wall covering,
combustible insulation or a combustible
water-resistive barrier shall comply with
Sections 1402.5.1 through 1402.5.5, as
applicable. Where compliance with NFPA
285 and associated acceptance criteria is
required in Sections 1402.5.1 through
1402.5.5, the exterior wall assembly shall be
tested in accordance with and comply with the
acceptance criteria of NFPA 285.”
This new section, and Subsections 1402.5.1
through 1402.5.5, consolidate the requirements
for exterior wall assemblies that contain
combustible components. Combustible exterior
wall assemblies must be evaluated for vertical
and lateral flame proposition according to NFPA
285 for Type I, II, III, and IV construction.
Section 1402.7 states:
“1402.7 Exterior wall veneers
manufactured using combustible
adhesives. Exterior wall assemblies on
buildings of Type I, II, III or IV construction
that are greater than 40 feet (12,192 mm)
in height above grade plane and contain an
exterior wall veneer manufactured using a
combustible adhesive to laminate a metal core
with noncombustible facing materials shall be
tested in accordance with, and comply with,
the acceptance criteria of NFPA 285, with the
adhesive level at the maximum application
rate intended for use. Combustibility
shall be determined in accordance with
Section 703.3.”
This new Section 1402.7 provides
requirements for metal claddings comprised
of a metal core and noncombustible facings
Three other
interrelated definitions
pertaining to roofs
were added or
revised, including
those for landscaped
roof, occupiable roof,
and vegetative roof.
30 • IIBEC Interface July/August 2024
that are laminated to the metal core using
combustible laminating adhesive. Section
1402.8, Vertical and Lateral Flame Propagation
Compliance Methods, adds requirements to
demonstrate compliance.
Under Section 1403, Materials, additional
sections have been added for fiber-mat
reinforced cementitious backer units (Section
1403.13) and insulated vinyl siding (Section
1403.14), which is also newly defined in
2024. Section 1403.2, Water-Resistive Barrier,
includes two new sentences that state, “The
intersection between the water-resistive
barrier material and fenestration openings
shall be flashed and assembled in accordance
with the fenestration manufacturer’s
installation instructions, or other approved
methods for applications not addressed by
the fenestration manufacturer’s instructions.
The water-resistive barrier material shall be
continuous to the top of walls and terminated
at penetrations and building appendages
in a manner to meet the requirements of
the exterior wall envelope as described in
Section 1402.2.” This language was added to
ensure that the water-resistive barrier (WRB) is
continuous at the top of walls and terminated
at penetrations.
Further changes to Section 1403.2,
Water-Resistive Barrier, include an additional
compliance method for WRBs and specific
requirements for horizontal applications of
WRBs. The additional compliance method
allows the WRB to be a foam plastic insulating
sheathing system complying with Section
1402.2 and the manufacturer’s instructions.
The new language requires that “No. 15 asphalt
felt and water-resistive barriers complying with
ASTM E2556 shall be applied horizontally…”
and be appropriately lapped.
With the addition of definitions (Section 202)
or materials (Section 1403), new sections have
been added to Section 1404, Installation of Wall
Coverings, for insulated vinyl siding (in Section
1404.15) and fiber-mat reinforced cementitious
backer units (Section 1404.19).
Changes to Section 1404.3, Vapor Retarders,
are related to the newly added term responsive
vapor retarder. An additional section, 1404.3.2,
has also been added on vapor barrier
installation, which reads:
“1404.3.2 Vapor retarder installation.
Vapor retarders shall be installed in accordance
with the manufacturer’s instructions or an
approved design. Where a vapor retarder also
functions as a component of a continuous air
barrier, the vapor retarder shall be installed as an
air barrier in accordance with the International
Energy Conservation Code.”
Additional changes to Section 1404.3
included modified or added footnotes to Table
1404.3(2), Vapor Retarder Options; Table
1404.3(4), Continuous Insulation with a Class
I or II Responsive Vapor Retarder; and a new
Table 1404.3(5), Continuous Insulation on
Walls without a Class I, II, or III Interior Vapor
Retarder.
A new Section 1404.4.1, Fenestration
Flashing, was added to Chapter 14. It states:
“1404.4.1 Fenestration flashing. Flashing
of the fenestration to the wall assembly shall
comply with the fenestration manufacturer’s
instructions or, for conditions not addressed by
the fenestration manufacturer’s instructions,
shall comply with one of the following:
1. The water-resistive barrier manufacturer’s
flashing instructions.
2. The flashing manufacturer’s flashing
instructions.
3. A flashing design or method of a registered
design professional.
4. Other approved methods.”
Cladding attachment for steel cladding and
wood was moved from Chapter 26 to Chapter
14 and now appears in Section 1404.5,
Fastening.
Other entirely new sections in Chapter 14
include Section 1409, Insulated Metal Panel
(IMP); Section 1411, Building-Integrated
Photovoltaic (BIPV) Systems for Exterior Wall
Coverings and Fenestration; and Section 1412,
Soffits and Fascias at Roof Overhangs.
CHAPTER 15: ROOF
ASSEMBLIES AND
ROOFTOP STRUCTURES
Two sections of Chapter 15 related to roof
drainage were altered significantly in the 2024
IBC. Section 1502.3, Scuppers, was deleted
in its entirety. The reasoning for the deletion
is that Section 1502.1 and Section 1502.2
already reference Section 1611 of the IBC
and Chapter 11 of the International Plumbing
Code;5 thus, Section 1502.3, Scuppers,
was duplicative.
Exceptions 1 and 2 of Section 1512.1 of the IBC
were revised due to IIBEC-facilitated code change
proposals. Section 1512.1 now reads:
“1512.1 General. Materials and methods
of application used for recovering or replacing
an existing roof covering shall comply with the
requirements of Chapter 15.
Exceptions:
1. Roof replacement or roof recover of existing
low-slope roof coverings shall not be
required to meet the minimum design slope
requirement of ¼ unit vertical in 12 units
horizontal (2-percent slope) in Section 1507
for roofs that provide positive roof drainage
and meet the requirements of Section
1608.3 and Section 1611.2.
2. Recovering or replacing an existing roof
covering shall not be required to meet the
requirement for secondary (emergency
overflow) drains or scuppers in Section
1502.2 for roofs that provide for positive
roof drainage and have been determined to
resist all design loads meet the requirements
of Section 1608.3 and Section 1611.2.
For the purposes of this exception, existing
secondary drainage or scupper systems
required in accordance with this code shall
not be removed unless they are replaced by
secondary drains or scuppers designed and
installed in accordance with Section 1502.2″.
These changes ensure that roofs are properly
evaluated during reroofing. Exception 1 of
Section 1512.1 of the IBC now requires a check
for ponding instability if an existing roof does
not meet minimum slope. Similarly, Exception 2
of Section 1512.1 of the IBC requires a check for
ponding instability if an existing roof does not
have secondary drainage.
In Section 1504.8, Wind Resistance
of Aggregate-Surfaced Roofs, additional
requirements were added related to the protection
of aggregate-surfaced roofs. Section 1504.8 reads:
“1504.8 Wind resistance of aggregatesurfaced
roofs. Parapets shall be provided
for aggregate surfaced roofs and shall comply
with Table 1504.8. Such parapets shall be
provided on the perimeter of the roof at all
exterior sides except where an adjacent wall
extends above the roof to a height at least
equivalent to that required for the parapet. For
roofs with differing surface elevations due to
slope or sections at different elevations, the
minimum parapet height shall be determined
based on each roof surface elevation, and at no
point shall the parapet height be less than that
required by Table 1504.8.
Exception: Ballasted single-ply roof coverings
shall be designed and installed in accordance
with Section 1504.5.”
Combustible exterior
wall assemblies must
be evaluated for
vertical and lateral
flame proposition
according to NFPA
285 for Type I, II, III,
and IV construction.
July/August 2024 IIBEC Interface • 31
Modifications to Table 1504.8 include
changing design wind speed to basic wind speed
and adding or modifying footnotes. Changes to
the footnotes are:
a. “Parapet height is measured vertically from
the top surface of the coping down to the
surface of the roof covering in the field of the
roof adjacent to the parapet and outbound of
any cant strip.
b. Interpolation shall be permitted for wind
speed, mean roof height and parapet height.
Extrapolation is not permitted.
c. Basic design wind speed, V, and wind
exposure shall be determined in accordance
with Section 1609.
d. Where the minimum required parapet height
is indicated to be 2 inches (51 mm), a gravel
stop shall be permitted and shall extend not
less than 2 inches (51 mm) from the roof
surface and not less than the height of the
aggregate.
e. The tabulated values apply only to conditions
where the topographic factor (K
zt) determined
in accordance with Chapter 26 of ASCE 7 is
1.0 or where K
zt is incorporated in the basic
wind speed in Section 1609.
f. For Exposure D, add 8 inches (203 mm) to
the parapet height required for Exposure C
and the parapet height shall not be less than
12 inches (305 mm).”
Section 1507.1.1, Underlayment, has been
simplified, while the related Table 1507.1.1(1),
Underlayment Types, has been revised to
incorporate changing design wind speed to basic
wind speed and adding various ASTM standards
for the various roof covering types. Additionally,
Table 1507.1.1(2), Underlayment Application, has
been revised significantly.
Deck requirements for wood shingles and
wood shakes have likewise been updated in
Sections 1507.8.1 and 1507.9.1, respectively.
A new Section 1511.9, Raised-Deck Systems
Installed over a Roof Assembly, adds many
provisions related to raised deck systems such
as those related to installation, fire classification,
pedestals or supports, structural requirements,
roof drainage, and accessibility and egress.
Exceptions in Section 1512.2, Roof
Replacement, were added or revised as such:
“Exceptions:
1. Where the existing roof assembly includes
an ice barrier membrane that is adhered
to the roof deck and the existing sheathing
is not water-soaked or deteriorated to the
point that it is not adequate as a base for
additional roofing, the existing ice barrier
membrane shall be permitted to remain in
place and covered with an additional layer
of ice barrier membrane in accordance with
Section 1507 where permitted by the roof
covering manufacturer and new ice barrier
underlayment manufacturer.
2. Where the existing roof includes a selfadhered
underlayment and the existing
sheathing is not water-soaked or deteriorated
to the point that it is not adequate as a base
for additional roofing, the existing selfadhered
underlayment shall be permitted
to remain in place and covered with an
underlayment complying with Tables
1507.1.1(1), 1507.1.1(2) and 1507.1.1(3).
3. Where the existing roof includes one layer of
self-adhered underlayment and the existing
layer cannot be removed without damaging
the roof deck, a second layer of self-adhered
underlayment is permitted to be installed
over the existing self-adhered underlayment
provided that the following conditions
are met:
3.1. It is permitted by the roof covering
manufacturer and self-adhered
underlayment manufacturer.
3.2. The existing sheathing is not watersoaked
or deteriorated to the point that
it is not adequate as a base for additional
roofing.
3.3. The second layer of self-adhered
underlayment is installed such that
buildup of material at walls, valleys, roof
edges, end laps and side laps does not
exceed two layers.”
Finally, an exception was added to Section
1512.3, Roof Recover, that reads:
“Exception: A roof recover shall not be
permitted where any of the following conditions
occur:
1. The existing roof or roof covering is
water-soaked or has deteriorated to the point
that the existing roof or roof covering is not
adequate as a base for additional roofing.
2. The existing roof covering is slate, clay,
cement or asbestos-cement tile.
3. The existing roof has two or more applications
of any type of roof covering.”
CHAPTER 16:
STRUCTURAL DESIGN
Tornado loads were added to Chapter 16,
Structural Design, due to their inclusion in
ASCE 7-22.2 More information on how to
design for wind loads is available in Wind Uplift
Pressures on Low-Slope Roofs3 and “Effects
of ASCE 7-22 Wind Load Provisions on Roof
Covering Design.”4
CHANGING THE CODE
There are several opportunities available to
those who are interested in playing a greater
role in the ICC’s code development process.
Codes are updated on a three-year cycle, and
code changes are being reviewed for the 2027
editions of the codes now. Contact Emily Lorenz,
senior director of technical services at IIBEC, at
elorenz@iibec.org for more information.
REFERENCES
1. International Code Council (ICC). 2024. International
Building Code. Country Club Hills, IL: ICC.
2. American Society of Civil Engineers (ASCE). 2022.
Minimum Design Loads and Associated Criteria
for Buildings and Other Structures. ASCE 7-22.
Reston, VA: ASCE.
3. Patterson, Stephen, and Madan Mehta. 2024. Wind
Uplift Pressures on Low-Slope Roofs. Fifth Edition.
Raleigh, NC: IIBEC.
4. Scott, Don. 2022. “Effects of ASCE 7-22 Wind Load
Provisions on Roof Covering Design.” In Proceedings of
2022 IIBEC International Convention and Trade Show,
in Orlando, FL, March 17–22, 2022. Raleigh, NC: IIBEC.
5. ICC. 2024. International Plumbing Code. Country Club
Hills, IL: ICC.
ABOUT THE AUTHOR
Emily Lorenz, PE,
F-ACI, specializes in
building code and
standards work and
advocacy, currently
representing the
International Institute
of Building Enclosure
Consultants as its senior
director of technical
services. Lorenz actively
participates as vice chair
of the Envelope Subcommittee developing the
commercial provisions of the 2024 International
Energy Conservation Code (IECC) and the
Envelope Subcommittee of ASHRAE 90.1, and as a
voting member of several committees, including
the 2024 IECC Commercial Committee, the ASTM
International Committee E60 on Sustainability,
and the American Concrete Institute’s building
code subcommittee on sustainability. She also
serves as an expert on ISO TC59\SC17\WG3
Environmental Declarations of Products.
Please address reader comments to
chamaker@iibec.org, including
“Letter to Editor” in the subject line, or
IIBEC, IIBEC Interface,
434 Fayetteville St., Suite 2400,
Raleigh, NC 27601.
EMILY LORENZ, PE,
F-ACI
32 • IIBEC Interface July/August 2024