An addition that is not structurally independent from an existing building must be designed and constructed such that the entire building conforms to the seismic force resistance requirements for new buildings unless the following two conditions listed below are met.  Furthermore, structural alterations to an existing building or its structural elements must also meet the following two conditions:

1. A.  The addition or structural alteration must comply with the requirements for new buildings; and
2. B.  Any existing lateral load-carrying structural element whose demand-capacity ratio with the addition(s) or structural alteration(s) considered is no more than 10 percent greater than its demand-capacity ratio with the addition(s) or structural alteration(s) ignored may be permitted to remain unaltered. For purposes of this paragraph, comparisons of demand-capacity ratios and calculation of design lateral loads, forces, and capacities must account for the cumulative effects of additions and structural alterations since original construction.