Cost of building ADU over existing garage

[Drew Rehman]

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?

[Jaysen Medhurst]

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."