2018 IBC and 2018 IEBC Changes Related to Wood Construction
David P. Tyree, P.E., C.B.O.
Changes to the 2018 International Building Code (IBC) and 2018 International Existing Buildings Code (IEBC) were approved by the International Code Council (ICC) during their 2015/2016 code development cycle. This article outlines changes to the code requirements for wood construction, the majority of which are changes to the IBC. Only a few changes for exterior balconies involve the IEBC.
For this article, all changes noted are to the IBC; any changes to the IEBC will be specifically called out. Accompanying the discussion of each code change is the ICC code change tracking number [colored/bracketed] that can be used to search for more information on the ICC website (iccsafe.org). Appendix A, available in the pdf version of this article and at www.awc.org, contains a strikethrough/underline format of changes where it is deemed helpful to understand the code changes mentioned herein.
Referenced Standards
American Wood Council (AWC) standards, as well as other code referenced standards, are updated [ADM94-16]. The 2018 National Design Specification® (NDS®) for Wood Construction and the 2018 Wood Frame Construction Manual for One-and-Two Family Dwellings were “Approved as Submitted” without modification.
The 2015 Special Design Provisions for Wind and Seismic (SDPWS) and 2015 Permanent Wood Foundation Design Specification are both still referenced in 2018 IBC.
The following updated APA-The Engineered Wood Association ANSI standards were also included [ADM94-16]:
- ANSI A190.1-2017 Structural Glued Laminated Timber
- ANSI/APA PRG-320-2017 Standard for Performance-Rated Cross-Laminated Timber
- ANSI/APA PRP 210-2014 Standard for Performance-Rated Engineered Wood Siding
- ANSI/APA PRR 410-2016 Standard for Performance-Rated Engineered Wood Rim Boards
- ANSI 117-2015 Standard Specification for Structured Glued Laminated Timber of Softwood Species
Approved Agencies
Certification report writing agencies were introduced into the definition of Approved Agency in Section 202. [ADM6-16, Part 1 AMPC1]
Exterior Balconies
- Clarifies removal of balconies from the scope of IBC Chapter 14 Exterior Walls since all balcony provisions were moved to IBC Chapter 7 Fire and Smoke Protection Features, IBC 705.2 and 706.5.2 [S1-16 AM]
- Requires that ventilation openings be provided similar to rafter spaces when the floor structure of exterior balconies and decks are enclosed [S7-16 AM]
- Incorporates the requirement from ASCE 7 for design live load of balconies and decks at 1.5 times the live load of the area served by the balcony or deck – not required to exceed 100 psf [S85-16]
- Requires detailing on plans of all impervious moisture barrier system elements (including manufacturer’s instructions when applicable) if the impervious moisture barrier option is used in IBC 2304.12.2.5 for wood framing supporting weather-exposed permeable floors, such as concrete or masonry slabs [ADM 77-16]
- Requires inspection of all impervious moisture barrier system elements, or special inspection can be utilized at the option of the code official if the impervious moisture barrier option is used in IBC 2304.12.2.5 for wood framing supporting weather-exposed permeable floors [ADM 87-16]
- Requires the impervious moisture barrier system to have positive drainage of water that infiltrates the permeable floor above the impervious moisture barrier when that option is used in accordance with IBC 2304.12.2.5 [S279-16 AMPC1]
- IEBC Chapter 1 revisions require details in construction documents and inspections for impervious moisture barriers used in exterior balconies [ADM 77-16 AMPC1].
An article on balcony detailing is available at this link: http://bit.ly/2AtN5k6.
Special Inspection and Structural Observation
- For structural observation, modifies the wind trigger from 110 mph to 130 mph for Risk Categories III or IV to match the current factored level of wind forces [S133-16]
- Clarifies the main wind force-resisting system fastening exception to special inspection in wood frame construction (based on nail spacing for sheathing exceeding 4 inches on center) at the panel edges. [S145-16 AM]
Other Changes
- Clarifies the definition of Light-frame Construction by removing “method of construction” from the definition [G2-16 AM]
- Revises Table 1604.3 Deflection Limits in footnote “d” to recognize different wood products’ creep behavior; specifically – seasoned lumber, structural glued laminated timber, prefabricated wood I-joists, SCL, cross-laminated timber and wood structural panels [S63-16 AM and S67-16]; includes correlating change to add roof live load to the load combination
- Clarifies that hardboard siding used structurally must conform to ANSI A135.6 and be identified by a label containing the approval agency [S258-16]
- Creates consistency with International Residential Code (IRC) wood structural panel roof sheathing nail size by inclusion of 8d common nail and adds the Roof Sheathing Ring Shank Nail (RSRS-01) to Table 2304.10.1 as options for roof sheathing attachment [S272-16]
- Corrects the 10d common nail length, removes redundant requirements for stud nailing, creates consistency with the IRC for roof sheathing attachment, and adds an option for deformed shank nail roof sheathing attachment [S273-16]
- Adds a reference to IBC 2304.9 for lumber decking in IBC 2304.11 for heavy timber [S276-16]
- Adds an alternative fastening schedule for the construction of mechanically laminated decking made from 2-inch nominal dimension lumber to IBC 2304.9.3.2 [S281-16]
- Corrects the staple description for stapled fiberboard shear walls in Table 2306.3(2) [S286-16]
- Updates Table 2308.4.1.1(2) for Southern Pine No. 2 in lieu of Southern Pine No. 1 for interior bearing wall girder and header spans, and includes the dropped and raised header distinction for spans [S288-16]
- Updates Table 2308.4.1.1(1) with Southern Pine No. 2 in lieu of Southern Pine No. 1 for exterior bearing wall girder and header spans and includes the dropped and raised header distinction for spans [S289-16]
- Adds prescriptive framing and connection requirements to IBC 2308.5.5.1 for single member (single ply) headers, consistent with the IRC, and coordinates code charging language with existing connection tables [S292-16]
- Updates references to current AWPA section numbering for preservative treatment used in permanent wood foundations and for wood shakes [S40-16]
- Clarifies that the minimum 5 psf horizontal live load applies to firewalls [S55-16 AM]
- Clarifies IBC 1615.1 regarding the applicability of structural integrity provisions in high rise buildings and precludes misinterpretation regarding frame buildings [S126-16]
- Revises IBC 1810.4.1.5 to require the removal of timber piles when a substantial and sudden change in rate of pile penetration occurs during driving [S233-16]
- Clarifies the IBC 2304.12.2.2 treated wood exception for posts supported on pedestals [S278-16 AM]
- Modifies IBC equations 23-1 and 23-2 for deflection of diaphragms and shear walls fastened by staples to be consistent with AWC SDPWS equations for nailed diaphragms and shear walls [S282-16 and S284-16]
- Clarifies in IBC 2308.2.3 that buildings with slab-on-grade floors can exceed a floor live load of 40 psf and still use the conventional wood frame construction provisions of IBC 2308 [S287-16]
Fire Retardant Treated Wood (FRTW)
- The approved modifications to IBC 2303.2.2 clarify that the “other means during manufacture” subsection is not intended to permit surface-protected products as outright replacements for fire retardant treated wood (FRTW), given the requirement for chemical impregnation into the wood. The modifications also preclude interpreting IBC 2303.2.2 as a ban or prohibition on surface-coated products. As has been the case for some time, wood products protected by surface treatments can be evaluated and approved by using the provisions of IBC 104.11 [S262-16 AM].
- Clarifies in IBC 2303.2.4 that FRTW must have the original product grade stamp in addition to the fire-retardant treatment labeling [S265-16]
ASCE 7-16 Minimum Design Loads and Associated Criteria for Buildings and Other Structures
IBC changes regarding ASCE 7-16 are likely to lead to some confusion for designers and code officials. While the purpose of this article is to outline IBC changes that were approved, a few instances where changes were defeated are specifically noted below to allow for discussion of code paths to compliance with load provisions.
- Updates reference to ASCE 7-16 [ADM94-16]
- Updates IBC wind and seismic load provisions to agree with updated criteria in ASCE 7-16 [S56-16 AM and S114-16 AM]
- Updates references in Chapter 18 seismic provisions to coordinate with ASCE 7-16 [S166-16]
- A proposal to update IBC snow load provisions to agree with updated criteria in ASCE 7-16 was defeated during online voting [S103-16 AMPC1 Defeated]. Therefore, the IBC allows three paths rather than one:
- Use the IBC to determine snow loads (Figure 1608.2 or Table 1608.2 for Alaska),
- Use IBC 1608.2, which references ASCE 7-16, and use the new tables for the western US and New Hampshire, or
- Use IBC 1608.2 to go to ASCE 7-16 which states that if an area is not in the new tables or exceeds the elevation limit (still a case study area), to then reference state produced maps which have greater detail for the western US and New Hampshire.
- A proposal removing LRFD and ASD load combinations based on reference to ASCE 7-16 was also defeated during online voting [S78-16 AM AMPC1 Defeated].
- On-line voting disapproved reference to ASCE 7-16 in IBC 1611 [S110-16 AMPC1 Defeated]. This has created a difference in requirements for secondary drains. ASCE 7-16 bases minimum requirements on a 15 min/100-yr event. IBC still uses the 1 hr/100-yr event for both primary and secondary minimum drain flow.
Fire Protection
- Clarifies in IBC 704 that the protection of “gang studs” and built-up columns in the walls of lightweight construction can be provided by the membranes of the rated walls in which they are located [FS7-15 AM]
- Reduces existing requirements in Table 705.2 on the location of building projections, such as roof overhangs [FS13-15 AS]
- Relocates Chapter 14 Exterior Walls fire-related provisions for balconies, projections, and bay and oriel windows to Chapter 7 Fire and Smoke Protection Features [FS15-15 AM]
- Revises IBC 706.2 to allow 3⁄4-inch plywood to run continuously through double firewalls in high seismic areas (Seismic Design Categories D and F) [FS29-15 AMPC1]
- Clarifies sprinkler, fire partition, and draftstopping requirements in IBC 708 and 718 for multifamily structures; one change gives clear criteria for the sprinkler protection of attics without draftstopping [FS42-15 AMPC1]
- Corrects certain prescriptive fire-resistance rated I-joist assembly description errors in Table 721.1(3) [FS129-15 AS and FS130-15 AS]
- Adds direct code references in IBC 803.11 to ASTM E 2579-13 and E 2404 for the mounting of laminate products, facings, and veneers with a wood substrate during testing [FS135-15 AS and FS136-15 AS]
- Revises IBC 803.3 to require that cross-laminated timber and heavy timber elements be subject to the normal flame spread limitations for exits similar to other materials in exit enclosures; a previous exception for heavy timber elements within exit enclosures is inappropriate for exposed mass timber elements that make up entire wall and ceiling sections [FS132-15 AS]
- Clarifies that fire officials can require round-the-clock fire watch for construction that exceeds 40 feet above grade [F329-16]
- Cleans up language permitting the use of FRTW sheathing in exterior walls of Type III and IV construction which is sometimes misinterpreted [G175-15 AS]
- Releases FRTW and CLT exterior walls from having an assembly minimum thickness in favor of simply requiring a minimum actual thickness solely for the CLT [G184-15 AS]; includes errata to the 2018 IBC as follows (errata shown “as written” using strikethrough/underline text):
602.4.1 Fire-retardant-treated wood in exterior walls.
Fire-retardant-treated wood framing complying with Section 2303.2 shall be permitted within exterior wall assemblies not less than 6 inches in thickness with a 2-hour rating or less.
602.4.2 Cross-laminated timber in exterior walls.
Cross-laminated timber complying with Section 2303.1.4 shall be permitted within exterior wall assemblies not less than 6 4 inches in thickness with a 2-hour rating or less, provided the exterior surface of the cross-laminated timber is protected by one the following:
- Fire-retardant-treated wood sheathing complying with Section 2303.2 and not less than 15⁄32-inch thick;
- Gypsum board not less than ½-inch thick; or
- A noncombustible material.
Heavy Timber and Mass Timber
- Makes clear that SCL should be considered equivalent to heavy timber and clarifies the appropriate distinctions between nominal, net finished, and actual dimensions for heavy timber, glulam, SCL, and CLT [G178-15 AS]
- Reorganizes heavy timber provisions aiding clear application of Type IV (heavy timber) construction requirements while also providing for separate application of code provisions that allow or specify the use of “heavy timber” elements outside of Type IV construction; moves certain heavy timber provisions from Chapter 6 to Chapter 23 and introduces a new table of minimum dimensions based on location within the building structure and loading condition [G179-15 AS; G180-15 AS] (Due to the extensive nature of these changes, the strikethrough/underline format is not shown in Appendix A. However, a summary of relocated sections is shown. The changes can be viewed on the ICC website.)
Construction Type
- Permits the use of roofs for various occupancies without classifying the building as one containing an additional story, thus assuring continued flexibility for buildings of wood construction types [G24-15 AMPC2]
- Permits performance-based alternatives for sound transmission design of floor assemblies using comparative engineering analysis [G190-15 AS]
Conclusion
The 2018 IBC and 2018 IEBC are both available from ICC (www.iccsafe.org) and represent the state-of-the-art codes for design and construction of buildings outside the scope of the International Residential Code. These codes reference the latest wood standards such as the 2018 NDS and include other important changes to requirements for wood construction. In some situations, a building designer may want to use a more current code provision or consensus standard that is recognized in the building code adopted by a jurisdiction. In those cases, building officials, in accordance with Section 104.11 of the International Building Code, are permitted to accept designs prepared in accordance with newer consensus reference standards. IBC 104.11 allows a jurisdiction to approve new technologies in materials and building construction, provided documentation supplied to the jurisdiction is found to assure equivalency in quality, strength, durability, and safety.▪