South Bay / Peninsula · field-data comparison
ADU cost · permits · timeline · which one wins
Two of the Bay Area's most permitting-mature jurisdictions, with radically different cost bases. San Jose's pre-approved plans bring detached ADUs under $475/sqft; Palo Alto's design culture and labor rates rarely close below $625/sqft for the same scope.
| Metric | San Jose | Palo Alto |
|---|---|---|
Detached ADU ($/sqft) All-in installed, 2026 USD. | $425–$550 | $560–$720 |
Garage conversion ($/sqft) | $250–$360 | $310–$440 |
Ministerial permit clock End-to-end, including agency back-and-forth. | 8–12 wk | 10–14 wk |
Discretionary review | 14–22 wk | 18–30 wk |
Permit story
San Jose has invested heavily in making ADUs easy. The Single Family ADU Process gives by-right approval to ADUs meeting objective standards, and the city's pre-approved plan program can collapse plan check to 4–6 weeks when a standard plan fits the lot. The main schedule variables are the Hillside Combining District on the foothills and which water utility serves the specific block.
Full San Jose field notes →Permit story
Palo Alto runs ADU permits through Planning and Development Services. State law applies, but the city's Heritage Tree Ordinance, Eichler design guidelines, and historic overlays mean a careful site visit before any design work. CPAU water + electric coordination is unique to Palo Alto.
Full Palo Alto field notes →San Jose
Palo Alto
San Jose
Palo Alto
The cheaper detached build, on paper, is San Jose (top-end $550/sqft vs $720/sqft). The faster permit clock belongs to San Jose (12 weeks vs 14 weeks ministerial). Those headlines flip once you factor in overlays, water-utility coordination, and design constraints — which is why we sketch the parcel before we ever quote a number.
Most detached San Jose ADUs land between $285K and $425K all-in. Garage conversions typically run $155K–$245K. Pre-approved plans on a standard lot are the cheapest path.
San Jose maintains a library of architect-designed ADU plans pre-vetted by the city. If your lot fits one, plan check can collapse to 4–6 weeks instead of the typical 8–12. We confirm fit during the first feasibility walk.
Yes — if the ADU meets San Jose's objective standards (setbacks, height, parking exemptions under state law), the city cannot deny it. No public hearing, no discretionary review.
Most detached Palo Alto ADUs land between $360K and $520K all-in. Conversions run $190K–$285K. Heritage tree protection and Eichler design requirements can push detached projects higher.
Strict. Designated trees and most mature oaks/redwoods are protected; we site the ADU around the critical root zone and often design pier-and-grade-beam foundations to avoid root impact.
Yes — design compatibility guidelines apply in Eichler tracts. Low-slope roofs, post-and-beam character, and compatible materials are reviewed.