Sacramento-built ADUs for the
Redwood City lot.

Here's the honest negative, and it's a real one: a big chunk of Redwood City sits on filled bay land. Redwood Shores especially — that whole peninsula east of 101 was diked and filled out of the marsh, and the water table under it runs high. Build a foundation there and you're often into a raised slab or a deeper system, plus a geotechnical report the city wants before you pour. The flats near Bair Island and the sloughs fall inside FEMA flood mapping too, so the finished floor has to sit above base flood elevation. On the hill it flips: Emerald Hills and upper Farm Hill are steep, and a downhill corner can need a stepped foundation, deeper footings, or piers into competent soil, with expansive clay making the geotech report close to mandatory. We check your parcel against the flood maps and the soil before we draw a slab — discovering a raised foundation after the design locks is how a budget blows up.

Set the Sacramento price sheet aside — the Peninsula is its own cost world. In Redwood City, a 624 sq ft one-bedroom detached ADU with mid-grade finishes runs roughly $360K to $450K all-in for 2025 into 2026 on a friendly flat lot, and a 960 sq ft two-bedroom with upgraded finishes lands closer to $510K to $640K. A hillside Emerald Hills build that needs a stepped foundation, or a Redwood Shores lot on fill that wants a raised system, pushes past those figures — the foundation is the swing item out here, not the kitchen. The rent makes it work: a one-bedroom pulls about $2,800 to $3,500 a month, a two-bedroom $3,600 to $4,700, and the job density around the Seaport and Redwood Shores tech offices plus a chronic Peninsula housing shortage keep a clean unit leased fast. Every prospect gets a fixed-price proposal after the free walk — a change order only happens if you upgrade a finish, never because we missed the soil, slope, access, or flood line.