Thank you all for your replies, especially DST148. Regarding the old lateral system, it never really had one except for sketchy unreinforced brick. Now, due to the size of renovation, the building has to withstand 2/3 of the full seismic force per NYCBC. Due to several door openings at critical...
Other NYC structures guys may be familiar with this situation. I have a project combining two 5-story brownstones, knocking out the middle party wall, re-framing each floor level and adding a new conc/cmu elevator core (13'x22'). Now the shaft needs to be designed to resist the total seismic...
