Garage Conversion to ADU

[Jonathan Schwerin]

Hi all,

I'm in contract on a house in Concord, CA and would like to convert the 2 car garage to an ADU. I've seen estimates of the cost to do this ranging from $30K up to $150K and beyond. Does anyone have a good way to get a better understanding of what the true cost will be? I've contacted a few contractors and am hoping to get some bids from them, but even so, I'm not sure I'll know what a "reasonable" bid is. Not looking to do anything fancy, just B quality.

The garage already has water hookups but I'm not sure about where the sewer line is yet...

Any suggestions?