Palo Alto
Santa Clara Co.Palo Alto's main homeowner resource is its 2025 ADU Guidebook, which covers ADU type, budgeting, financing, and booking the Planner on Duty.
Every city's ADU rules, straight from the source.
Rules vary a lot between neighbouring cities, and the fastest way to a straight answer is the jurisdiction's own page. These are the official ones for every city we build in, from Palo Alto down to Gilroy — no aggregators, no competitor blogs.
10 of these cities run a pre-approved plan program, where the city has already reviewed a set of ADU designs. Building a detached unit from one drops the city's decision clock from 60 days to 30 — and the plan can come from any agency in California, not just your own city. How that works, and who runs a program.
Cities reorganise their sites often. If a link has moved, the department page listed on the card will get you there — or just ask Keyli and she'll search the city's site live.
Start here
Santa Clara ADU (aduscc.org)
The best single starting point in the county. A collaboration between every Santa Clara County city and the County itself, run by the County Planning Collaborative with the Cities Association — free step-by-step guidance from 'ADU 101' through move-in, covering both incorporated cities and unincorporated land.
Open →County of Santa Clara — Planning & Development
The authority for parcels in UNINCORPORATED Santa Clara County — land outside any city's limits, which is permitted by the County rather than a city. Also runs a pre-approved ADU plan program.
Open →California HCD — ADU handbook and state law
The statewide baseline every city builds on. Useful for understanding which rules your city cannot override, and what the state guarantees regardless of local ordinance.
Open →By city
Listed north to south. Parcels outside a city's limits are permitted by the County, not the city — see “Start here” above.
East Palo Alto
San Mateo Co.Los Altos
Santa Clara Co.Los Altos Hills
Santa Clara Co.Publishes pre-approved plans already cleared by California HCD, plus a cost calculator. Plans still need a siting conversation with planning, but get a streamlined review.
Mountain View
Santa Clara Co.Also runs a separate path for legalizing an existing unpermitted ADU.
Sunnyvale
Santa Clara Co.No parking is required for an ADU. Short-term rental is prohibited for ADUs approved after 1 Jan 2020.
Cupertino
Santa Clara Co.Santa Clara
Santa Clara Co.Most ADU projects go straight to a building permit. A new attached second-story ADU over a single-story home is the exception and needs architectural review.
Milpitas
Santa Clara Co.Also runs an ADU Incentive Program and a Safe ADU legalization path for existing unpermitted units.
San José
Santa Clara Co.The deepest set of resources in the county — pre-approved plans, an ADU FAQ, a documented plan-review process, and a path for ADU condominium conversion under AB 1033.
Campbell
Santa Clara Co.Runs an Express Plan Check that can bring simple ADU approvals down from months to about a week. ADUs skip land-use entitlement and go straight to the Building Division.
Saratoga
Santa Clara Co.Monte Sereno
Santa Clara Co.The City Council approved a 50% reduction in building permit and plan check fees for a new ADU, including conversions of an existing pool house or garage.
Los Gatos
Santa Clara Co.Morgan Hill
Santa Clara Co.Gilroy
Santa Clara Co.Also publishes a path for legalizing unpermitted ADUs and JADUs.
Rules are one thing. Your lot is another.
An ordinance tells you what's allowed in the abstract. Setbacks, easements, utility runs and what's already standing decide what's actually buildable — that's what the free site walk is for.