Cost of building ADU over existing garage

3 Replies

I'm seeing building costs for detached ADUs in Santa Clara at about $250 to $300 sq ft.


Does anyone know if it is any cheaper to build the ADU above an existing garage?


What are the potential construction cost increases and decreases by going this route?

@Drew Rehman

$250-300 are fairly standard current prices for new construction in California. Hard to say what savings you may or may not achieve with your strategy. You will likely need to reinforce the garage walls a little. You still need to run plumbing and electrical. Sometimes that can mean cutting into concrete floors to connect to existing plumbing. Really depends on layout of house and locations of utilities. 

Wouldn't be that expensive, @Drew Rehman . $250-300/sq ft looks like ground-up prices. That being said, you have to be darn sure that you can put an ADU above the garage. Beyond the normal code/zoning disclaimers, the ceiling joist of a garage are not intended to support living space. I doubt they are suitable, meaning they'd all have to be replaced. Reframing would be a big job. Then there's utilities. Surely, no water/sewer to the garage currently. You'll also have to upgrade the electrical service. It's not as simple as slapping up some drywall and posting it "For Rent."

@Drew Rehman Your property might vary a lot in Santa Clara but I'm assuming it's older.  Likely you have the water heater in the garage like most CA homes.  Possibly your washer and dryer are also in the garage if it's an older CA home which means you have electrical and maybe plumbing.

For the most accurate costs, a contractor can help you and it depends on your construction but there are many homes in the Santa Clara county that are the split level homes and rooms are built over the garages. It's going to be more like a home construction than an ADU.