Section 502A — ADDITIONS

502 A .1 General. Additions to any building or structure shall comply with the requirements of the California Building Code for new construction. Alterations to the existing building or structure shall be made to ensure that the existing building or structure together with the addition are not less complying with the provisions of the California Building Code than the existing building or structure was prior to the addition. An existing building together with its additions shall comply with the height and area provisions of Chapter 5 of the California Building Code . Where a new occupiable roof is added to a building or structure, the occupiable roof shall comply with the provisions of the California Building Code.

Exception: In-filling of floor openings and nonoccupiable appendages such as elevator and exit stairway shafts shall be permitted beyond that permitted by the California Building Code.

502 A .1.1 Risk category assignment. Where the addition and the existing building have different occupancies, the risk category of each existing and added occupancy shall be determined in accordance with Section 1604 A .5.1 of the California Building Code . Where application of that section results in a higher risk category for the existing building compared with the risk category for the existing building before the addition, such a change shall be considered a change of occupancy and shall comply with Section 506 A of this code. Where application of that section results in a higher risk category for the addition compared with the risk category for the addition by itself, the addition and any systems in the existing building required to serve the addition shall comply with the requirements of the California Building Code for new construction for the higher risk category.

502 A .1.2 Creation or extension of nonconformity. An addition shall not create or extend any nonconformity in the existing building to which the addition is being made with regard to accessibility, structural strength, supports and attachments for nonstructural components, fire safety, means of egress or the capacity of mechanical, plumbing or electrical systems.

Exception: Nonconforming supports and attachments for nonstructural components that serve the addition from within the existing building need not be altered to comply with California Building Code Section 1613 A unless the components are part of the addition’s life-safety system or are required to serve an addition assigned to Risk Category IV.

502 A .2 Flood hazard areas. For buildings and structures in flood hazard areas established in California Building Code, Section 1612 A .3, any addition that constitutes substantial improvement of the existing structure , as defined in Chapter 2, shall comply with the flood design requirements for new construction, and all aspects of the existing structure shall be brought into compliance with

5A-4 2025 CALIFORNIA EXISTING BUILDING CODE

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the requirements for new construction for flood design. For new foundations, foundations raised or extended upward, and replacement foundations, the foundations shall be in compliance with the requirements for new construction for flood design.

For buildings and structures in flood hazard areas established in California Building Code, Section 1612 A .3, any additions that do not constitute substantial improvement of the existing structure , as defined in Chapter 2, are not required to comply with the flood design requirements for new construction, provided that both of the following apply:

1. The addition shall not create or extend a nonconformity of the existing building or structure with the flood-resistant construction requirements.
2. The lowest floor of the addition shall be at or above the lower of the lowest floor of the existing building or structure or the lowest floor elevation required in Section 1612 A of the California Building Code .

502 A .3 Existing structural elements carrying gravity load. Any existing gravity load-carrying structural element for which an addition and its related alterations cause an increase in design dead, live or snow load, including snow drift effects, of more than 5 percent shall be replaced or altered as needed to carry the gravity loads required by the California Building Code for new structures. Any existing gravity load-carrying structural element whose vertical load-carrying capacity is decreased as part of the addition and its related alterations shall be considered to be an altered element subject to the requirements of Section 503 A .3. Any existing element that will form part of the lateral load path for any part of the addition shall be considered to be an existing lateral load-carrying structural element subject to the requirements of Section 502A.4 .

502 A .4 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 lateral force-resisting system of the existing structure and its addition acting together as a single structure shall comply with Section 1609 A and 1613A of the California Building Code .

Exceptions: For incidental and minor additions:

1. Any existing lateral load-carrying structural element whose demand-capacity ratio with the addition considered is not more than 10 percent 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 Sections 1609 A and 1613 A of the California Building Code . For purposes of this exception, comparisons of demand-capacity ratios and calculation of design lateral loads, forces and capacities shall account for the cumulative effects of additions and alterations since original construction. When calculating demand-capacity ratios for wind, the date of original construction shall be permitted to be taken as the date of completion of a prior addition, alteration or repair in compliance with Section 1609 A of the California Building Code or the code wind forces in effect at the time. When calculating demand-capacity ratios for earthquake, the date of original construction shall be permitted to be taken as the date of completion of a prior addition, alteration or repair in compliance with Section 304A.3.4 of this code or the full seismic forces in effect at the time.

2. Drift limits based on original design code shall be permitted to be used in lieu of the drift limits required by ASCE 7.