Buildings and structures undergoing Level 3 structural alterations or buildings in which the seismic base shear is increased by more than 10 percent or in which the seismic base shear capacity is decreased by more than 10 percent because of alterations shall comply with this section. Changes in base shear and base shear capacity shall be calculated relative to conditions at the time of the original construction.
- Buildings of Group R occupancy with no 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 Building Code of New York State.
- Where such alterations involve only the lowest story of a building and the change of occupancy provisions of Chapter 9 do not apply, only the lateral-force-resisting components in and below that story need comply with this section.
- If the building's seismic base shear capacity has been increased since the original construction, the percentage changes shall be permitted to be calculated relative to the increased value.
An engineering evaluation and analysis that establishes the structural adequacy of the altered structure shall be prepared by a registered design professional and submitted to the code enforcement official.
Where more than 30 percent of the total floor and roof areas of the building or structure have been or are proposed to be involved in structural alteration within a 12-month period, the evaluation and analysis shall demonstrate that the altered building or structure complies with the Building Codeof New York State for wind loading and with reduced Building Codeof New York State level seismic forces as specified in Section 506.1.1.3 for seismic loading. For seismic considerations, the analysis shall be based on one of the procedures specified in Section 506.1.1.1. The areas to be counted toward the 30 percent shall be those areas tributary to the vertical load-carrying components, such as joists, beams, columns, walls and other structural components that have been or will be removed, added or altered, as well as areas such as mezzanines, penthouses, roof structures and in-filled courts and shafts.
Where not more than 30 percent of the total floor and roof areas of the building are involved in structural alteration within a 12-month period, the evaluation and analysis shall demonstrate that the altered building or structure complies with the loads applicable at the time of the original construction or of the most recent substantial structural alteration as defined by Section 807.5.2.