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?

[Chen Zhou]

@Daisy Chou

You can do it for less for 1 and 2, I think. 3 would definitely cost less.

I recently got permit approval in SJ (Willow Glen) for a 630 sqft attached ADU + 170 sqft addition to the existing unit. Here's my cost breakdown:

Architect + structural engineer	$ 7,000
Park fee	$ 4,450
School fee	$ 2,192
Permit application	$ 2,653
Permit Issuance	$ 9,416
Contractor (estimated)	$ 170,000
Inspections (estimated)	$ 4,000
Landscaping and other miscellaneous	$ 300
Total (estimated)	$ 200,011

Let me know if you need referrals for contractors. Good luck with your project!