Appraisal of a property with an ADU unit

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I am working on refinance of my single family home with an recently developed ADU unit in the bay area that cost more than 300k to build and the appraiser only added 75k in value for the in law unit

The ADU unit is detached 2 bed/2bath/den/kitchen with its own address and pge meter.

Is that a norm in the bay area for ADU properites or the appraiser had no clue on what he is doing.

If this is true then practically I lost money and 2 years of my time to get the design/approval and construction done and it looks like adding ADU does not make any sense in the bay area.