Section 503A — ALTERATIONS

503 A .1 General. Alterations to any building or structure shall comply with the requirements of the California Building Code for new construction. Alterations shall be such that the existing building or structure is not less complying with the provisions of the Califor- nia Building Code than the existing building or structure was prior to the alteration.

Exceptions:

An existing stairway shall not be required to comply with the requirements of Section 1011 of the California Building Code where the existing space and construction does not allow a reduction in pitch or slope.
Handrails otherwise required to comply with Section 1011.11 of the California Building Code shall not be required to comply with the requirements of Section 1014.7 of the California Building Code regarding full extension of the handrails where such extensions would be hazardous because of plan configuration.

503 A .2 Flood hazard areas. For buildings and structures in flood hazard areas established in Section 1612 A .3 of the California Build- ing Code, any alteration 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 the requirements for new construction for flood design.

For buildings and structures in flood hazard areas established in Section 1612 A .3 of the California Building Code any alterations 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.

503 A .3 Existing structural elements carrying gravity load. Any existing gravity load-carrying structural element for which an alteration causes 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 loadcarrying structural element whose gravity load-carrying capacity is decreased as part of the alteration shall be shown to have the capacity to resist the applicable design dead, live and snow loads including snow drift effects required by the California Building Code for new structures.

503 A .4 Existing structural elements carrying lateral load. Except as permitted by Section 503 A .13, where the alteration increases design lateral loads, results in a prohibited structural irregularity as defined in the California Building Code, ASCE 7, or decreases the

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capacity of any existing lateral load-carrying structural element, the lateral force-resisting system of the altered building or structure shall meet the requirements of Section s 1609 A and 1613A of the California Building Code .

Exceptions: For incidental and minor alterations:

Any existing lateral load-carrying structural element whose demand-capacity ratio with the alteration considered is not more than 10 percent 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 Section s 1609 A and 1613A of the California Building Code . Reduced seismic forces, to 75 percent of those in Section 1613A, shall be permitted. The same methodology shall be used for the altered and unaltered structures. 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 or reduced seismic forces in effect at the time.
Buildings in which the increase in the demand-capacity ratio is due entirely to the addition of rooftop-supported mechanical equipment individually having an operating weight less than 400 pounds (181.4 kg) and where the total additional weight of all rooftop equipment placed after initial construction of the building is less than 10 percent of the roof dead load. For purposes of this exception, “roof” shall mean the roof level above a particular story.
Increases in the demand-capacity ratio due to lateral loads from seismic forces need not be evaluated for the installation of rooftop photovoltaic panel systems where the additional roof dead load due to the system, including ballast where applicable, does not exceed 5 pounds per square foot (psf) (0.2394 kN/m [2] ) and does not exceed 10 percent of the dead load of the existing roof. 4. Drift limits based on original design code shall be permitted to be used in lieu of the drift limits required by ASCE 7.

503 A .5 Seismic Design Category F. Not permitted by OSHPD.

503 A .6 Bracing for unreinforced masonry parapets on reroofing. Not permitted by OSHPD.

503 A .7 Anchorage for concrete and reinforced masonry walls. Not permitted by OSHPD.

503 A .8 Anchorage for unreinforced masonry walls in major alterations. Not permitted by OSHPD.

503 A .9 Bracing for unreinforced masonry parapets in major alterations. Not permitted by OSHPD.

503 A .10 Anchorage of unreinforced masonry partitions in major alterations. Not permitted by OSHPD.

503 A .11 Substantial structural alteration. Not permitted by OSHPD.

503 A .12 Roof diaphragms resisting wind loads in high-wind regions. Not permitted by OSHPD.

503 A .13 Voluntary lateral force-resisting system alterations. Structural alterations that are intended exclusively to improve the lateral force-resisting system and are not required by other sections of this code shall not be subject to the structural requirements of Section 503 A except as described below, provided that all of the following apply:

With the alteration complete, the capacity of existing structural systems to resist forces is not reduced.
New structural elements are detailed and connected to existing or new structural elements as required by the selected design criteria in accordance with Section 503A.4 or 304A.3.4 of this code. Exception: New lateral force-resisting systems designed in accordance with the California Building Code are permitted to be of a type designated as “Ordinary” or “Intermediate” where ASCE 7 Table 12.2-1 states these types of systems are not permitted.
Supports and attachments for nonstructural elements removed and reinstalled to facilitate the work comply with the Cali- fornia Building Code for new construction.
The alterations do not create a structural irregularity as defined in ASCE 7 or make an existing structural irregularity more

severe.

Exception: Condition 4 need not be satisfied where the work complies with Section 304A.3.4 of this code.

503 A .14 Smoke compartments. Shall comply with California Building Standards Code.

503 A .15 Refuge areas. Shall comply with California Building Standards Code.

503 A .16 Reserved.

503 A .17 Ambulatory care facilities. Where a work area exceeds 50 percent of the building area and the work area includes an existing ambulatory care facility, the following shall be provided:

A smoke compartment in accordance with Section 422.3 of the California Building Code where the alteration results in an ambulatory care facility greater than 10,000 square feet on one story.
Separation from adjacent spaces in accordance with Section 422.2 of the California Building Code, where any such facility has the potential for four or more care recipients are to be incapable of self-preservation at any time.

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503 A .18 Reserved.

503 A .19 Reserved.

503 A .20 Two-way communications systems. Where the work area for alterations exceeds 50 percent of the building area and the building has elevator service, a two-way communication systems shall be provided where required by Section 1009.8 of the Califor- nia Building Code.