Chapter 5 of the CEBC is hereby adopted by reference except as amended herein.
91.2.501.1. Scope. The provisions of this division shall control the alternation, addition and change of occupancy of existing buildings and structures, [BSC] including state-regulated structures in accordance with Section 501.1.2 of the CEBC. In addition to the requirements of the CEBC, existing buildings and structures shall comply with the applicable regulations of Divisions 81, 82, 83, 84, 85, 86, 88, 89, 91, 93, 95 and 97 of the Los Angeles Building Code (LABC) at Article 1, Chapter IX of the LAMC, Appendix A Chapters A1 and A2 of the LAEBC, and the voluntary earthquake hazard reduction standards of Divisions 92, 94 and 96 of Article 1, Chapter IX of the LAMC.
91.2.502.5. Existing Structural Elements Carrying Lateral Load. Where the addition is structurally independent of the existing structure, existing lateral load-carrying structural elements shall be permitted to remain unaltered. Where the addition is not structurally independent of the existing structure, the existing structure and its addition acting together as a single structure shall be shown to meet the requirements of Sections 1609 and 1613 of the California Building Code using full seismic forces. For purposes of CEBC Section 502, compliance with ASCE 41, using a Tier 3 procedure and the two level performance objective in CEBC Table 303.3.1 for the applicable risk category, shall be deemed to meet the requirements of CBC Section 1613, with procedures established by the Department.
EXCEPTIONS:
1. Except for Unreinforced Masonry (URM) Buildings:
Any existing lateral load-carrying structural element whose demand-capacity ratio with the addition considered is no more than 10% greater than its demand-capacity ratio with the addition ignored shall be permitted to remain unaltered. For purposes of calculating demand-capacity ratios, the demand shall consider applicable load combinations with design lateral loads or forces in accordance with CBC Sections 1609 and 1613. For purposes of this exception, comparisons of demand-capacity ratios and calculations of design lateral loads, forces and capacities shall account for the cumulative effects of additions and alterations since original construction.
The additions do not create structural irregularity as defined in ASCE 7 or make an existing structural irregularity more severe.
2. Unreinforced Masonry (URM) Buildings:
Any existing lateral load-carrying structural element on an unreinforced masonry building whose demand-capacity ratio with the addition considered less than 10% greater than its demand-capacity ratio with the addition, must comply with CEBC Appendix Chapter A1. When the demand-capacity ratio with the addition considered is 10% or greater than its demand-capacity ratio with the addition ignored, shall be designed per CBC Division 16.
91.2.503.4. Existing Structural Elements Carrying Lateral Load. (Amended by Ord. No. 187,719, Eff. 1/23/23.) Except as permitted by CEBC Section 503.13, where the alteration increases design lateral loads in accordance with CBC Section 1609 or 1613, or where the alteration results in a prohibited structural irregularity as defined in ASCE 7, or where the alteration decreases the capacity of any existing lateral load-carrying structural element, the structure of the altered building or structure shall be shown to meet the requirements of CBC Sections 1609 and 1613. Reduced seismic loads shall be permitted providing the reduced seismic load is not less than the original building permitted seismic loads. For purposes of CEBC Section 503, compliance with ASCE 41, using the performance objective in CEBC Table 303.3.1 for the applicable risk category, shall be deemed to meet the requirements of CBC Section 1613, and using the performance objective in CEBC Table 303.3.2 for the applicable risk category, shall be deemed to meet the requirements of reduced seismic loads, with procedures established by the Department.
EXCEPTIONS:
1. Except for Unreinforced Masonry Buildings (URM):
Any existing lateral load-carrying structural element whose demand-capacity ratio with the alteration considered is no more than 10% greater than its demand-capacity ratio with the alteration ignored shall be permitted to remain unaltered. For purposes of calculating demand-capacity ratios, the demand shall consider applicable load combinations with design lateral loads or forces in accordance with CBC Sections 1609 and 1613. Reduce seismic forces shall be permitted. For purposes of this exception, comparisons of demand-capacity ratios and calculations of design lateral loads, forces and capacities shall account for the cumulative effects of additions and alterations since original construction.
The alternations do not create structural irregularity as defined in ASCE 7 or make an existing structural irregularity more severe.
2. Unreinforced Masonry (URM) Buildings:
Any existing lateral load-carrying structural element on an URM building whose demand-capacity ratio with the alteration considered is less than 10% greater than its demand-capacity ratio with the alteration, it shall comply with CEBC Appendix Chapter A1. When the demand-capacity ratio with the alteration considered is 10% or greater than its demand-capacity ratio with the alteration ignored, it shall be designed per CBC Chapter 16.
Structural analysis per CEBC Appendix Chapter A1 is required for any alterations to crosswalls or diaphragms.
91.2.506.5.3. Seismic Loads (seismic force-resisting system). (Amended by Ord. No. 187,719, Eff. 1/23/23.) Where a change of occupancy results in a building being assigned to a higher risk category, or where the change is from a Group S or U occupancy to an occupancy other than Group S or Group U, the building shall satisfy the requirements of Section 1613 of the California Building Code for the new risk category using full seismic forces. For purposes of this Section, compliance with ASCE 41, using a Tier 3 procedure and the two-level performance objective in CEBC Table 303.3.1 for the applicable risk category, shall be deemed to meet the requirements of CBC Section 1613, with procedures established by the Department.
EXCEPTIONS:
1. Where the area of the new occupancy is less than 10% of the building area, the occupancy is not changing from a Group S or Group U, and the new occupancy is not assigned to Risk Category IV, compliance with this Section is not required. The cumulative effect of occupancy changes over time shall be considered.
2. When a change of use results in a structure being reclassified from Risk Category I or II to Risk Category III and the structure is located where the seismic coefficient, SDS, is less than 0.33, compliance with the seismic requirements of CBC Sec. 1613 is not required.
3. Unreinforced masonry bearing wall buildings assigned to Risk Category III and to Seismic Design Category A or B shall be permitted to use Appendix Chapter A1 of this code.
4. Where the change is from a Group S or Group U occupancy and there is no change of risk category, use of reduced seismic forces shall be permitted.
For a change of occupancy of an existing commercial or industrial building to residential use, all existing buildings shall be analyzed for 75% of the design earthquake ground motion, as defined in CBC Section 1613, but in no event shall there be a reduction in the capacity of the seismic force resisting system where that system provides a greater level of protection than the minimum requirements established by this Code.
For an existing URM building, structural analysis per CBC Chapter 16 is required if the risk category is changed to III or IV. Structural analysis per CEBC Appendix A1 is required if rating classification per LABC Division 88, Table 88-A is changed to I or II.
For URM buildings with an approved occupant load greater than 100, the occupant load may be increased by a maximum of 10% without changing the rating class or risk category.
The most restrictive requirement of CEBC Sections 502 (Addition), 503 (Alternation), 405 (Repair) and 506 (Change of Occupancy) shall apply.