Cost of building an ADU in Fremont

[Daisy Chou]

My SFH is located on a 11,000 sf lot with 2800 sf living space (single story).

We are considering to build an ADU 900 square feet.

There are 3 options:

1. detached ADU

2. attached ADU

3. internal/conversion ADU that is located entirely within the 2800sf, making it 900 ADU and 1900 principal residence

We were told that #1/#2 would cost around 350k and #3 around 250k.  Are these numbers reasonable?