Pub. 4 2023-2024 Issue 3

The 2021 IBC code changes are critical for the Architecture, Engineering and Construction (AEC) industry. As various jurisdictions adopt the latest version, understanding the structural changes and their impacts on building assembly, design costs and project schedules becomes paramount. This article will introduce a few impactful code updates, including: • Mass timber additions to the building code. • Updates on construction types and fire resistance. • Local Code Amendments to the 2021 IBC. • Other key updates to consider in design. Mass Timber Addition to the Building Code Mass Timber has received significant attention in the 2021 IBC updates. While the 2018 IBC allowed Mass Timber Structures up to 85 feet and 6 stories (Type IV HT), the 2021 IBC has introduced four new construction types that extend the potential of Mass Timber up to 18 stories with a total building height of up to 270 feet. The new types are: • Type IV-HT (Heavy Timber) • Type IV-C (CLT – Mostly Exposed) • Type IV-B (CLT – Mostly Protected) • Type IV-A (CLT – Completely Protected) In conjunction with the new mass timber construction types, the 2021 IBC provides the following provisions: • Prescriptive fire-resistance requirements added in IBC 722.7. • Approval of mass timber connections per IBC 2304.10.1. • Testing and Sealing requirements for intersections and abutting edges per 703.6 and 703.7. • Connection Protection Inspection per 110.3.5. The 2021 IBC Sections 508.4.4.1 and 509.4.1 emphasize fire safety and resistance for mass timber, introducing requirements like ½” gypsum separation for mass timber elements serving as fire barriers in Type IV-B or IV-C constructions. For mass timber buildings over 120 feet tall, redundant fire pump requirements are added INTRODUCTION TO 2021 IBC Code Updates Photo Credit: IBC 2021 Photo Credit: iccsafe.org BY CHRIS BRATT, BHB STRUCTURAL BUILDING ELEMENT TYPE I TYPE II TYPE III TYPE IV TYPE V ABABABABC HT AB Primary structural framef (see Section 202) 3a b 2a,b,c 1b,c 0c 1b,c 0 3a 2a 2a HT 1b,c 0 Bearing walls Exteriore, f 3 2 1 0 2 2 3 2 2 2 1 0 Interior 3a 2a 1 0 1 0 3 2 2 1/HTg 1 0 Nonbearing walls and partitions Interiord 0 0 0 0 0 0 0 0 0 See Section 2304.11.2 0 0 Floor construction and associated secondary structural members (see Section 202) 2 2 1 0 1 0 2 2 2 HT 1 0 Roof construction and associated secondary structural members (see Section 202) 1 1b 1b,c 1b,c 0c 1b,c 0 1 1 1 1 HT 1b,c 0 For SI: 1 foot = 304.8 mm. a. Roof supports: Fire-resistance ratings of primary structural frame and bearing walls are permitted to be reduced by 1 hour where supporting a roof only. b. Except in Group F-1, H, M and S-1 occupancies, fire protection of structural members in roof construction shall not be required, including protection of primary structural frame members, roof framing and decking where every part of the roof construction is 20 feet or more above any floor immediately below. Fire-retardant-treated wood members shall be allowed to be used for such unprotected members. c. In all occupancies, heavy timber complying with Section 2304.11 shall be allowed for roof construction, including primary structural frame members, where a 1-hour or less fire-resistance rating is required. d. Not less than the fire-resistance rating is required. e. Not less than the fire-resistance rating based on fire separation distance (see Table 705.5). f. Not less than the fire-resistance rating as referenced in Section 704.10. g. Heavy timber bearing walls supporting more than two floors or more than a floor and a roof shall have a fire resistance rating of not less than 1 hour. 27

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