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506.4.3 Revise this section as follows:
506.4.3 Seismic loads (seismic force-resisting system). Where a change of occupancy results in a building being assigned to a higher risk category, or where the occupant load of the entire building or structure is increased by more than 10 percent and by more than 100 persons as compared to the occupant load of the existing legal use or the use for which the building was originally permitted, the building shall comply with Section 303.3.1 for the new risk category using full seismic forces.
Exceptions:
1.
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.
2.
When a change of occupancy or use involves only one story of a building or structure, only the lateral force resisting elements in that story and all lateral force resisting elements below need comply with reduced seismic forces in Section 303.3.2.
3.
A change from a Group R, Division 3 to a Group R, Division 1 or Division 2 Occupancy caused by the construction of a third dwelling unit in the lowest story of a building or structure shall comply with reduced seismic forces in Section 303.3.2 as provided in Exception 2 above.
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