Property tax reassessment for second story addition in CA

[DA Nguyen]

Hi all

Already emailed the Assessor’s Office but thought I would post here in case anyone has first hands experience.

I’m considering adding on a second story to our house. I know that in CA only new improvements would be assessed and we don’t plan on making major changes to the first floor besides perhaps knocking down two interior walls to create an open floor plan. But a second story addition involves significant structural reinforcement and MEP updates to the existing structure.

Two things I’m unsure about are:

1. Would this trigger a reassessment of the entire property?

2. If not, will the cost approach likely be used? Specifically let’s say the full economic cost is 350$/sqft but houses are being sold for 700$/sqft, the addition would still only be assessed on the $350/sqft basis?