ADU Property Tax Assessment in Bay Area, California

[Dre Ho]

For those that have built ADUs in California, especially the Bay Area, have you seen your property tax increase a lot after the ADU build? Do you know how property tax is assessed for ADU? I know they are assessed separately from the main home, but I'm wondering what the assessor uses to consider the property value. Is it builder cost, $/square footage, comps around the area, etc? I'm just curious because I'm building a detached 940 sq ft 2 bed/2bath detached ADU in San Mateo, CA and I'm nervous that the property tax will increase significantly.