Santa Clara County · Land use · Duplex
Where is a duplex allowed in Santa Clara County?
In Santa Clara County, a duplex is allowed in 3 base zones (R1S, R2 and R3, all with a condition), needs a permit in 5 (R3S, CN, CG, OA and A1, 3 with a condition) and not allowed in 8 (Santa Clara County use tables, read October 2026).
Key points
- Allowed: R1S, R2 and R3
- Needs a permit: R3S, CN, CG, OA and A1
- Not allowed: R1, R1E, RHS, ML, MH, RS, OS/F and SCA
Find your lot's zone on the city zoning map, then read its row. Every status below was read from the Santa Clara County Municipal Code use tables (read October 2026). Base zones only. General information, not legal advice — check with the city before you apply.
Zones where a duplex can go
Santa Clara County's code calls this use “Two-Family”. Each row links to the use table it comes from. A zone marked “see note” has a condition in the code, for example upper floors only or a larger lot.
| Zone | Status | Code |
|---|---|---|
| R1S | Allowed — see note Note 1: Single-family dwellings, including certain additions, and duplexes, may be subject to the building site approval provisions of Section C12-300 et seq. of the County Ordinance Code. Note 2: In R1S districts, ASA is required for new single-family residences on lots smaller than 10,890 square feet (0.25 acre), excluding housing development pursuant to Section 65852.21 of the California Government Code. ASA is not required for additions or remodels of existing dwellings. | § 2.30.020 |
| R2 | Allowed — see note Note 1: Single-family dwellings, including certain additions, and duplexes, may be subject to the building site approval provisions of Section C12-300 et seq. of the County Ordinance Code. | § 2.30.020 |
| R3 | Allowed — see note Note 1: Single-family dwellings, including certain additions, and duplexes, may be subject to the building site approval provisions of Section C12-300 et seq. of the County Ordinance Code. | § 2.30.020 |
| R3S | Needs an architecture and site approval (asa) — see note Note 1: Single-family dwellings, including certain additions, and duplexes, may be subject to the building site approval provisions of Section C12-300 et seq. of the County Ordinance Code. | § 2.30.020 |
| CN | Needs an use permit and architecture and site approval — see note Note 5: Commercial/residential mixed uses are permitted in CN and CG districts subject to use permit and ASA. | § 2.40.020 |
| CG | Needs an use permit and architecture and site approval — see note Note 5: Commercial/residential mixed uses are permitted in CN and CG districts subject to use permit and ASA. | § 2.40.020 |
| OA | Needs an use permit and architecture and site approval | § 2.40.020 |
| A1 | Needs an use permit and architecture and site approval | § 2.50.020 |
Zones where it is not allowed
What else applies
- State law: SB 9 (Gov. Code § 65852.21) allows two homes on most single-family lots with a ministerial permit, also where this table says no.
- Not covered here: Combining districts (-os, -sm, -h, -bw, -d1, -d2 etc.) can change allowed uses; Chapter 2.10 use classification definitions are not in the packet; Other base districts of the county outside Chapters 2.20-2.50, if any. Overlay zones and specific plans can also change the answer.
Other uses in Santa Clara County
Who this affects
Frequently asked questions
Can I have a duplex in the R3S zone in Santa Clara County?
Only with an architecture and site approval (asa). Santa Clara County's use table lists it that way in R3S (§ 2.30.020). The code adds a condition: “Single-family dwellings, including certain additions, and duplexes, may be subject to the building site approval provisions of Section C12-300 et seq. of the County Ordinance Code.”
Can I have a duplex in the R1 zone in Santa Clara County?
No. Santa Clara County's use table does not allow it in R1 (§ 2.30.020).
Can I have a duplex in the R1S zone in Santa Clara County?
Yes, with a condition. Santa Clara County's use table lists it as allowed in R1S (§ 2.30.020). The code adds a condition: “Single-family dwellings, including certain additions, and duplexes, may be subject to the building site approval provisions of Section C12-300 et seq. of the County Ordinance Code. In R1S districts, ASA is required…”
General information, not legal advice.
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