Section 503 — ALTERATIONS

Alterations to any building or structure shall comply with the requirements of the California Building Code or Califor- nia Residential Code, as applicable, for new construction. Alterations shall be such that the existing building or structure is not less complying with the provisions of the California Building Code or California Residential Code, as applicable, than the existing building or structure was prior to the alteration, except that the structural elements need only comply with Sections 503.2 through 503.12.

Exceptions:

1. 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.
2. 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.
3. Where provided in below-grade transportation stations, existing and new escalators shall be permitted to have a clear width of less than 32 inches (815 mm). 4. [BSC] For state-owned buildings, including those owned by the University of California and the California State University and the judicial council, the requirements of Section 503.4 are replaced by the requirements of Sections 317 through 322.

[BS] 503.2 Flood hazard areas. For buildings and structures in flood hazard areas established in Section 1612.3 of the California Building Code, or Section R306 of the California Residential Code, as applicable, any alteration that constitutes substantial improvement of the existing structure 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 1612.3 of the California Building Code, or Section R306 of the California Residential Code, as applicable, any alterations that do not constitute substantial improvement of the existing structure are not required to comply with the flood design requirements for new construction.

[BS] 503.3 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 load-carrying 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.

Exceptions:

1. Buildings of Group R occupancy with not more than five dwelling or sleeping units used solely for residential purposes where the altered building complies with the conventional light-frame construction methods of the California Building Code or the provisions of the California Residential Code .
2. Buildings in which the increased dead load is due entirely to the addition of a second layer of roof covering weighing 3 pounds per square foot (0.1437 kN/m [2] ) or less over an existing single layer of roof covering. [DSA-SS, DSA-SS/CC] Excep- tion 2 is not permitted.

[BS] 503.4 Existing structural elements carrying lateral load. Except as permitted by Section 503.13, where the alteration increases design lateral loads, results in a prohibited structural irregularity as defined in ASCE 7, or decreases the 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 1609 of the California Building Code and Section 304.3.2 of this code.

Exceptions:

1. 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

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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 1609 of the California Building Code and Section 304.3.1 or 304.3.2 of this code. 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 demandcapacity 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 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 304.3.1 or Section 304.3.2, Item 1 or 3, or the full or reduced seismic forces in effect at the time.

2. 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.
3. 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.

[BS] 503.5 Seismic Design Category F. Where the work area exceeds 50 percent of the building area, and where the building is assigned to Seismic Design Category F, the lateral force-resisting system of the altered building shall meet the requirements of Section 1609 of the California Building Code and Section 304.3.2 of this code. Supports and attachments for nonstructural components serving any portion of the building with a use included in Risk Category IV shall comply with Section 1613 of the California Building Code or shall comply with ASCE 41 using an objective of Position Retention nonstructural performance with the BSE-1E earthquake hazard level.

f the California Building Code and Section 304.3.2 of this code. Supports and attachments for nonstructural components serving any portion of the building with a use included in Risk Category IV shall comply with Section 1613 of the California Building Code or shall comply with ASCE 41 using an objective of Position Retention nonstructural performance with the BSE-1E earthquake hazard level.

[BS] 503.6 Bracing for unreinforced masonry parapets on reroofing. Where the intended alteration requires a permit for reroofing and involves removal of roofing materials from more than 25 percent of the roof area of a building assigned to Seismic Design Category D, E or F that has parapets constructed of unreinforced masonry, the work shall comply with Section 304.3.2 by evaluation of the existing condition or by installation of parapet bracing to resist out-of-plane seismic forces.

[BS] 503.7 Anchorage for concrete and reinforced masonry walls. Where the work area exceeds 50 percent of the building area, the building is assigned to Seismic Design Category C, D, E or F and the building’s structural system includes concrete or reinforced masonry walls with a flexible roof diaphragm, the alteration shall comply with Section 304.3.2 by evaluation of the existing condition or by installation of wall anchors at the roof line.

[BS] 503.8 Anchorage for unreinforced masonry walls in major alterations. Where the work area exceeds 50 percent of the building area, the building is assigned to Seismic Design Category C, D, E or F and the building’s structural system includes unreinforced masonry bearing walls, the alteration shall comply with Section 304.3.2 by evaluation of the existing condition or by installation of wall anchors at the floor and roof lines.

[BS] 503.9 Bracing for unreinforced masonry parapets in major alterations. Where the work area exceeds 50 percent of the building area, and where the building is assigned to Seismic Design Category C, D, E or F, and the building has parapets constructed of unreinforced masonry, the alteration shall comply with Section 304.3.2 by evaluation of the existing condition or by installation of parapet bracing to resist out-of-plane seismic forces.

[BS] 503.10 Anchorage of unreinforced masonry partitions in major alterations. Where the work area exceeds 50 percent of the building area, or where the building is assigned to Seismic Design Category C, D, E or F, and the building has unreinforced masonry partitions and nonstructural walls, the alteration work shall include evaluation of the existing condition or removal, anchoring or alteration of any such partitions or walls within the work area and adjacent to egress paths from the work area, to comply with Section 304.3.2.

area, or where the building is assigned to Seismic Design Category C, D, E or F, and the building has unreinforced masonry partitions and nonstructural walls, the alteration work shall include evaluation of the existing condition or removal, anchoring or alteration of any such partitions or walls within the work area and adjacent to egress paths from the work area, to comply with Section 304.3.2.

[BS] 503.11 Substantial structural alteration. Where the work area exceeds 50 percent of the building area and where work involves a substantial structural alteration, the lateral load-resisting system of the altered building shall satisfy the requirements of Section 1609 of the California Building Code and Section 304.3.2 of this code. Where the building is assigned to Seismic Design Category D or F, supports and attachments for nonstructural components required to serve any portion of the building with a use included in Risk Category IV shall comply with Section 1613 of the California Building Code or shall comply with ASCE 41 using an objective of Position Retention nonstructural performance with the BSE-1E earthquake hazard level.

Exceptions:

1. Buildings of Group R occupancy with not more than five dwelling or sleeping units used solely for residential purposes that are altered based on the conventional light-frame construction methods of the California Building Code or in compliance with the provisions of the California Residential Code .
2. Where the intended alteration involves structural components of the lowest story of a building, only the lateral loadresisting system above that story need not comply with this section.

[BS] 503.12 Roof diaphragms resisting wind loads in high-wind regions. Where the intended alteration requires a permit for reroofing and involves removal of roofing materials from more than 50 percent of the roof diaphragm of a building or section of a building located where the basic wind speed, V, is greater than 130 mph (58 m/s) in accordance with Figure 1609.3(2) of the California

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Building Code, roof diaphragms, connections of the roof diaphragm to roof framing members, and roof-to-wall connections shall be evaluated for the wind loads specified in Section 1609 of the California Building Code, including wind uplift. If the diaphragms and connections in their current condition are not capable of resisting 75 percent of those wind loads, they shall be replaced or strengthened in accordance with the loads specified in Section 1609 of the California Building Code .

Exception: Buildings that have been demonstrated to comply with the wind load provisions in ASCE 7—88 or later editions.

[BS] 503.13 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, provided that all of the following apply:

1. With the alteration complete, the capacity of existing structural systems to resist forces is not reduced.
2. New structural elements are detailed and connected to existing or new structural elements as required by the selected design criteria. 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.
3. Supports and attachments for nonstructural elements removed and reinstalled to facilitate the work comply with the Cali- fornia Building Code for new construction.
4. 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 304.3.2, Item 3.

In Group I-2 occupancies where the alteration is on a story used for sleeping rooms for more than 30 care recipients, the story shall be divided into not less than two compartments by smoke barrier walls in accordance with Section 407.5 of the California Building Code as required for new construction.

Where alterations affect the configuration of an area utilized as a refuge area, the capacity of the refuge area shall not be reduced below the required capacity of the refuge area for horizontal exits in accordance with Section 1026.4 of the Cali- fornia Building Code .

Where the horizontal exit also forms a smoke compartment, the capacity of the refuge area for Group I-2 and I-3 occupancies and ambulatory care facilities shall not be reduced below that required in Sections 407.5.3, 408.6.2, 420.6.1 and 422.3.2 of the California Building Code, as applicable.

Group R-2.1 occupancies that are being altered and where the work area is greater than 50 percent of the aggregate building area shall be classified in accordance with Section 310.3.1 of the California Building Code .

503.16.1 Smoke Barriers in Group R-2.1 , Condition 2. In Group R-2.1 occupancies where the work area is on a story used for sleeping rooms for more than 30 care recipients, the story shall be divided into not less than two compartments by smoke barrier walls in accordance with Section 420.6 of the California Building Code .

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:

1. 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.
2. 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.

In Group E occupancies, where the work area exceeds 50 percent of the building area, enhanced classroom acoustics shall be provided in all classrooms with a volume of 20,000 cubic feet (565 m [3] ) or less. Enhanced classroom acoustics shall comply with the reverberation time in Section 808 of ICC A117.1.

In Group E occupancies, Group B educational occupancies and Group I4 occupancies, egress doors with locking arrangements designed to keep intruders from entering the room shall comply with Section 1010.2.8 of the California Building Code .

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 .