The provisions of Section 806 of IEBC are adopted by reference with the following modifications:
1. Revise exception 1 to Section 806.2 to read:
"1. Buildings of Group R-5 occupancy where the altered building complies with the conventional light-frame construction methods of the Chicago Building Code."
2. Revise Section 806.3 to read:
"806.3 Existing structural elements resisting lateral loads.
Except as allowed by Section 806.4, where the alteration increases design lateral loads, or where the alteration results in prohibited structural irregularity as defined in ASCE 7, or where the alteration decreases the capacity of any existing lateral load-carrying structural element, the structure of the altered building or structure shall meet the requirements of Sections 1609 and 1613 of the Chicago Building Code. Reduced seismic forces shall be allowed.
Exception: 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 allowed 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 and 1613 of the Chicago Building Code. Reduced seismic forces shall be allowed. 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."