One wall shared,
a full second home off your Rancho Cordova house.

Your shared wall stops being an ordinary interior wall the moment two separate dwellings sit on either side of it. Code wants a rated separation then. Usually that means a one-hour fire assembly running floor to roof — the correct gypsum layers, fireblocking at every penetration, and a sound-rated cavity so your tenant isn't living inside your TV. This is the part that surprises people. On the 1950s and 60s tracts up near the old Mather field and the Aerojet area, we've opened a wall expecting clean framing and found aluminum-era wiring and board sheathing that won't carry the rating as-is. We draw the assembly on the plans, build it to the listed spec, and the City inspector signs off on a wall that physically exists.

The reason an attached ADU usually pencils cheaper than a detached one sits right in the name. You tap the slab, the SMUD service and the water line already running to your house, instead of trenching sixty or eighty feet across the lot to a freestanding cottage. One honest caveat: at 750 sq ft the City can require a separate water meter, and on the older north-side homes with 100-amp panels SMUD often wants a service upgrade before a second kitchen's load goes on — so we size the unit knowing where those lines sit. An attached unit also fits a tighter side yard than a detached one needs, which helps on the modest Anatolia and Sunridge yards south of Highway 50. We've landed flat-lot attached jobs in the low $200Ks where shared utilities did the heavy lifting.