One shared wall,
a full second home tied to your Granite Bay house.

Your shared wall stops being a plain interior wall the second two separate dwellings sit on either side of it. Code wants a rated separation then. Usually that's a one-hour fire assembly running floor to roof — correct gypsum layering, fireblocking at every penetration, and a sound-rated cavity so your tenant isn't living inside your TV. This is the part people don't see coming. On a custom Granite Bay home we've opened a wall expecting clean framing and found a structural beam and HVAC trunk lines that complicate the rating. So the existing side often needs work too. We draw the assembly on the plans, build it to the listed spec, and the Placer County inspector signs off on a wall that physically exists.

The reason an attached ADU usually pencils cheaper than a detached one sits right there in the name. You're tapping the foundation, the PG&E service and the water line already running to your house, instead of trenching a few hundred feet across an acre-plus Granite Bay parcel to a freestanding cottage — through ground that may be solid granite. One honest caveat: at 750 sq ft the County can require a separate water meter, and on the bigger estate homes PG&E sometimes wants service work before adding a second kitchen's load. So we size the unit knowing where those lines sit. An attached unit also tucks into a tighter side yard than a detached build needs, which helps when a horse setup or septic field eats the open ground. We've landed shared-utility attached projects in the low $200Ks.