Local zoning · Atherton

Atherton — Zoning

Zoning under the Atherton local zoning and planning code, with the controlling citations.

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Last reviewed: July 3, 2026

Overview

This page summarizes the Town of Atherton’s zoning rules as codified in Title 17 (Zoning). It explains the Town’s base districts, overlay districts, and the most decision-relevant development standards (height, setbacks, floor area, lot coverage) with chapter citations so you can check the ordinance text. For procedural details (permits, building code compliance) see the linked topic pages below and verify parcel-specific questions with the Town Planner.

Quick internal links you will see in the page (first mention only): the town’s zoning overview is at Atherton zoning & planning overview (/us/california/atherton); land-use rules are under Atherton Land Use (/us/california/atherton/land-use); numeric standards are at Atherton Development Standards (/us/california/atherton/development-standards); on-site vehicle rules are at Atherton Parking (/us/california/atherton/parking); the Town’s design controls are at Atherton Design Review (/us/california/atherton/design-review); overlays are summarized at Atherton Overlay Districts (/us/california/atherton/overlay-districts); accessory dwelling units are at Atherton ADUs (/us/california/atherton/adu); and where the state code matters see the California Building Standards Code (/us/california/building-codes).

How Title 17 is organized (brief)

Title 17 divides Atherton into base zoning districts (for example R-1A, R-1B, POS, PFS) and overlay districts (for example Parker Avenue (P), RM-10, RM-20, RM-40). Use tables in each chapter to find allowed uses and the development standards that apply to an individual lot; uncertain map boundaries are interpreted by the Town Planner. See § 17.30.030–.080 for district rules and overlay identification .

District-by-district breakdown

Note: each district name below is the Town’s actual designation and the controlling code citation follows the short description.

R-1A (Residential district R-1A)

  • Purpose: Reserve land for single‑family residential development consistent with the General Plan; implements one dwelling unit per lot and supports second dwelling units and home occupations where allowed. § 17.32.010–.020 .
  • Typical permitted uses: single‑family dwelling (P), group homes, employee housing (limited); other uses require a conditional use permit (CUP). See Table 17.32.030-1. § 17.32.030 .
  • Key dimensional standards (development standards chapter):
    • Maximum main building height: standard 30 ft; vertical sidewalls/columns limit 22 ft; may be increased (up to 34 ft main building, 28 ft sidewalls) with additional setbacks or a special structure permit. § 17.32.040(A) .
    • Setbacks / measurement: see the general setback measurement rules in Chapter 17.54. § 17.54.030 .
    • Lot size/new-lot rules: tied to Title 16 lot-size requirements. § 17.32.040(B) .

Where it applies: base single‑family residential neighborhoods mapped in the zoning plan; boundary interpretation by Town Planner § 17.30.060 .

R-1B (Residential district R-1B)

  • Purpose and uses: Similar intent to R-1A (single‑family) but with specific development standards for smaller lots; allowed uses include single‑family dwellings (P), second dwelling units (subject to ADU rules), home occupations, and certain institutional uses by CUP. § 17.33.010–.030 .
  • Key dimensional standards:
    • Maximum main building height: 28 ft (vertical sidewalls/columns not to exceed 18 ft). § 17.33.040(A)(1) .
    • Maximum FAR: often expressed as a percentage or by formula for lots under one acre (for example, an alternative formula is used for lots < 43,560 sq ft). See § 17.33.040(C) for the calculation details. § 17.33.040(C) .
    • Special rules for dormers, basements, and accessory buildings referenced by section. § 17.33.040 .

Where it applies: the R‑1B mapped neighborhoods listed in the zoning plan; smaller single‑family parcels. See Table 17.33.030‑1 for allowed uses .

POS (Park and Open Space)

  • Purpose: preserve parks, recreation, watershed, and natural-resource lands. § 17.34.010–.020 .
  • Typical permitted uses: park/recreation facilities, country clubs, watershed protection, and limited compatible uses subject to development standards and permits. § 17.34.030 .
  • Standards: chapter sets development standards to implement General Plan open‑space policies. § 17.34.010 .

PFS (Public Facilities and Schools) and Multifamily Overlays RM‑10, RM‑20, RM‑40

  • Base PFS purpose: public facilities and school sites; when combined with multifamily overlays, specific multifamily development rules apply. See the overlay identification rules § 17.30.080 .
  • RM‑10: a multifamily overlay that can allow multifamily development (see allowed‑use tables); specifics and objective design standards are in chapter 17.36 references. § 17.30.080 .
  • RM‑20/RM‑40: density overlays applied to portions of PFS lots to permit multifamily housing by‑right within specified mapped areas:
    • RM‑20 allows up to 20 units/acre (minimum 12 units/acre). § 17.36.070 .
    • RM‑40 (applies notably to Menlo College portions) allows up to 40 units/acre (minimum 24 units/acre) with specific height and sidewall controls. § 17.36.070 .
    • Height limits: RM‑20 main building max 34 ft; RM‑40 main building max 48 ft (with mid‑point/flat‑roof caveats). Vertical sidewall limits vary and are lower next to R‑1 properties (see R‑1 adjacent sidewall rules). § 17.36.070(A) .
    • Setbacks: base 40 ft setback is indicated for RM overlays, with step‑backs as height increases; R‑1 adjacent setbacks require larger separations (minimum 50 ft where adjacent to R‑1 unless an RM overlay applies). § 17.36.070(B–C) .

Where they apply: only to mapped portions of PFS parcels and where the zoning map identifies the overlays; see the Town zoning map and the Housing Element list referenced in the code. § 17.36.070 .

Parker Avenue Overlay (P)

  • Purpose: Address a cluster of sub‑acre lots along Parker Avenue (applies to lots in R‑1A that front a 70‑ft right‑of‑way). The overlay modifies R‑1A standards to allow more floor area while reducing some height limits to mitigate impacts. § 17.37.010–.020 .
  • Key modified standards:
    • Height (Parker): standard max 28 ft; vertical sidewalls/columns not to exceed 20 ft. § 17.37.040(A) .
    • FAR / floor area formula: floor area = (lot size × 0.165) + 1,500 sq ft (plus a cap on 2nd‑story area). § 17.37.040(B) .
    • Front setback (single‑story ≤15 ft): 23 ft 3 in. § 17.37.040(C) .
  • Where it applies: mapped Parker Avenue overlay parcels — consult the zoning map or the Town Planner for precise boundaries. § 17.37.010 .

Quick reference table — common decision‑relevant standards

District Typical permitted primary uses Typical max height Example front setback Max FAR / floor area Code Reference
R-1A Single‑family (P), second units per ADU chapter 30 ft standard; up to 34 ft with permit/added setback See general measurement rules (varies) See § 17.32.040 for lot‑size & FAR rules § 17.32.030–.040
R-1B Single‑family (P), second units (subject to ADU chapter), home occupations 28 ft main building; sidewall limit 18 ft 30 ft (general front yard baseline) 18% typical; alternative formula for <1 acre lots § 17.33.030–.040
POS Parks, recreation, watershed protection N/A (open space) N/A Site‑specific per § 17.34 § 17.34.010–.030
RM‑20 (overlay) Multifamily on mapped PFS portions 34 ft (main) 40 ft baseline; increases with height Density up to 20 units/acre § 17.36.070
RM‑40 (overlay) Multifamily (Menlo College mapped area) 48 ft max (with mid‑point caveat) 40 ft baseline; increased with height Density up to 40 units/acre § 17.36.070
Parker (P) overlay Modified R‑1A for Parker Ave lots 28 ft (main); sidewalls max 20 ft 23 ft 3 in (single‑story ≤15 ft) floor area = lot×0.165 + 1,500 sq ft § 17.37.010–.040

(For measurement rules and exceptions see Chapter 17.42 Building Height & Measurement and Chapter 17.54 Yard Measurements and Projections.) § 17.42.020–.030; § 17.54.030 file

Practical guidance and interpretation tips

  • Floor area: Atherton uses both percentage FAR and specific formulas for smaller lots (example: R‑1B and Parker overlay formulas). Always run the formula (or check the Table in the district chapter) before sizing a project. See § 17.33.040(C) and § 17.37.040(B) file.
  • Sidewall vs. overall height: many districts distinguish vertical sidewalls/columns from overall roof height; dormer rules and mid‑point rules can allow some rooftop massing while limiting tall vertical walls next to neighbors. Check § 17.32.040(A), § 17.33.040(A), and § 17.36.070(A) for district-specific language filefile.
  • R‑1 adjacent protections: where a parcel abuts an R‑1 property, the code often requires larger setbacks (for example 50 ft in RM overlays). Check § 17.36.070(C) for RM adjacent setback rules. § 17.36.070(C) .
  • Basements & parking: basements can be excluded from FAR measurement in certain low‑grade situations; below‑grade parking may enable a higher FAR in some districts (check the FAR rules and Chapter 17.44 for basements). § 17.44.040; § 17.35.030.D file.
  • Design review and site details: the Town has design review rules — consult Atherton Design Review (/us/california/atherton/design-review) and verify whether your project requires design review early. Specific triggers and objective standards are in separate chapters or design guidelines; exact cross‑references are not fully extracted here. Not found in retrieved materials: a single consolidated design‑review trigger table. Verify with the Town Planner. Not found in retrieved materials .
  • ADUs: second dwelling units are permitted in many residential districts but must comply with chapter 17.52 and state ADU law; see Atherton ADUs (/us/california/atherton/adu) and § 17.52 for local ADU rules. § 17.33.030 Note 2; § 17.52 file.

Checklist (what an applicant must demonstrate / provide to satisfy zoning)

  • Confirm zoning district for the parcel from the Town zoning map and any overlays; request boundary interpretation from the Town Planner if uncertain. § 17.30.060
  • Demonstrate proposed use is listed as permitted (P) or identify required permit (CUP, special structure permit, etc.) in the district allowed‑use table. § 17.30.030; district tables file
  • Show compliance with development standards: height, setbacks, FAR/floor area, lot coverage, and accessory building limits using the controlling district chapter (e.g., § 17.32.040, § 17.33.040, § 17.36.070). filefile
  • Provide floor‑area calculations and show whether any basement or covered area is exempt from FAR under Chapter 17.44. § 17.44.040
  • Site plan that shows driveway location, vehicle access compliance, and vision triangle; note maximum driveway width 26 ft where specified. § 17.36.070(D)
  • Landscape screening plan consistent with Chapter 17.50 and heritage tree protections; irrigation and installation timing requirements must be shown. § 17.36.070(C)
  • If proposing ADU or second unit, show compliance with Chapter 17.52 and state ADU law. § 17.33.030 Note 2; § 17.52 file
  • If project uses or changes an overlay (RM‑10, RM‑20/40, Parker (P)), demonstrate compliance with the overlay chapter(s). § 17.30.080; § 17.37; § 17.36.070 filefile

Risks & Ambiguities

Issue Why it matters What to verify
Overlay boundary (RM‑20/40, P) Development rights and density depend on whether a parcel is inside an overlay. Verify overlay mapping for the parcel; ask Town Planner to interpret boundaries per § 17.30.060. § 17.30.060
R‑1 adjacent setbacks RM projects adjacent to R‑1 parcels face larger setback/sidewall limits (e.g., 50 ft). Noncompliance can force redesign. Confirm whether the adjacent parcel is R‑1 or has an RM overlay; check § 17.36.070(C). § 17.36.070(C)
FAR formulas for small lots Different formulas apply to lots under one acre or other thresholds; floor‑area caps in Parker overlay differ. Run the specific district formula from § 17.33.040(C) or § 17.37.040(B); check for rounding/minimums. § 17.33.040(C) file
Basement & below‑grade parking treatment Whether basement area counts toward FAR depends on grade measurement; miscalculation can cause a code violation. Confirm with Chapter 17.44 and measure per § 17.44.040; verify grade measurement approach under § 17.42.030. § 17.44.040; § 17.42.030 file
Design review triggers Projects may require discretionary design review — adds time/conditions. Confirm triggers and objective design standards with the Planning Department; consolidated triggers not found in retrieved materials. Not found in retrieved materials

Plain-English Summary

Atherton’s zoning (Title 17) is primarily single‑family residential (districts R‑1A and R‑1B) with mapped overlay districts (Parker Avenue, RM‑10, RM‑20, RM‑40) that modify density and dimensional rules on specific parcels; the key compliance checks are allowed use, height/sidewall limits, setbacks (including larger R‑1‑adjacent setbacks), floor area calculations, lot coverage, and overlay eligibility — all of which are spelled out by district chapter and measurement rules in Chapters 17.32–17.38 and Chapters 17.42–17.44. See the district chapters cited below for the exact text and verify parcel boundaries with the Town Planner. § 17.32–17.38; § 17.42–17.44 file

Source References

  • Title 17 (Zoning), Town of Atherton — Chapter and section citations used in this page (Atherton Municipal Code, current through Ordinance 677):
    • § 17.32.010–.040 (Residential district R‑1A)
    • § 17.33.010–.040 (Residential district R‑1B)
    • § 17.34.010–.030 (POS Park & Open Space)
    • § 17.36.070 (Multifamily Overlay RM‑20/40 standards)
    • § 17.37.010–.040 (Parker Avenue Overlay P)
    • § 17.30.060–.080 (Interpretation of district boundaries; overlay identification)
    • § 17.42.020–.030 (Building height & measurement)
    • § 17.44.040 (Basement/FAR rules)
    • § 17.54.030 (Setback measurement rules)
    • Chapter 17.52 (Accessory Dwelling Units — local ADU chapter reference)
  • Town web pages (internal GoCodebook menu links used above):
    • Atherton zoning & planning overview: /us/california/atherton
    • Atherton Land Use: /us/california/atherton/land-use
    • Atherton Development Standards: /us/california/atherton/development-standards
    • Atherton Parking: /us/california/atherton/parking
    • Atherton Design Review: /us/california/atherton/design-review
    • Atherton Overlay Districts: /us/california/atherton/overlay-districts
    • Atherton ADUs: /us/california/atherton/adu
    • California Building Standards Code (state): /us/california/building-codes

If you need parcel‑specific confirmation (overlay boundaries, measured setbacks, or whether a specific proposed element triggers design review), verify with the Town Planner and ask for a written interpretation per § 17.30.060. § 17.30.060

Sources

Retrieved passages

  • Atherton Zoning Code (§ 1) High relevance
  • Atherton Zoning Code (Title 17) High relevance
  • Atherton Zoning Code (Title 17) High relevance
  • Atherton Zoning Code (Title 17) High relevance
  • Atherton Zoning Code (Title 17) High relevance
  • Atherton Zoning Code (§ 4) High relevance
  • Atherton Zoning Code (section 17.42.030.) High relevance
  • Atherton Zoning Code (chapter 17.40.) High relevance
  • Atherton Zoning Code (chapter 17.42) High relevance
  • Atherton Zoning Code (Section 17021.5.) High relevance
  • Atherton Zoning Code (Title 17) High relevance
  • Atherton Zoning Code (chapter 17.40) High relevance

Cited sections

Frequently asked questions

What can I build on an R-1A lot in Atherton?

You can build a single‑family dwelling and accessory uses listed in Table 17.32.030‑1 (home occupations, group homes, certain employee housing), subject to the R‑1A development standards (height, setbacks, lot coverage) in § 17.32.030–.040 file.

What are Atherton setback requirements for residential lots?

Setback measurement rules are in Chapter 17.54; district chapters (for example § 17.32.040, § 17.33.040) provide the district minima and step‑backs for height, and tables such as Table 17.35.030.B.2‑1 list side‑yard minima that scale with lot width. See § 17.54.030 and the relevant district development standards. § 17.54.030; § 17.35.030 file

Do I need design review in Atherton?

Design review triggers and procedures are managed by the Town; the Town maintains design review standards and review processes (consult Atherton Design Review). A consolidated trigger table was not extracted here — verify whether your project triggers design review with the Planning Department. Not found in retrieved materials

What is the maximum height for a house in R-1B?

The maximum main building height in R‑1B is 28 ft, with vertical sidewall/column limits (example 18 ft sidewall limit); see § 17.33.040(A) for dormer exceptions and measurement rules. § 17.33.040(A)

How does the Parker Avenue overlay change rules for small lots?

The Parker Avenue (P) overlay modifies R‑1A for the Parker Avenue cluster: it allows more floor area (floor area = lot×0.165 + 1,500 sq ft), but reduces some height limits (standard max 28 ft; sidewalls 20 ft) and sets a 23 ft 3 in front setback for single‑story portions under 15 ft. See § 17.37.010–.040

Are second dwelling units (ADUs) allowed in Atherton?

ADUs/second dwelling units are referenced and permitted in multiple residential district tables but must comply with the Town’s Chapter 17.52 rules and applicable state ADU law; check § 17.33.030 Note 2 and Chapter 17.52 for local ADU requirements and link to Atherton ADUs for local guidance. § 17.33.030; Ch. 17.52 file

How is floor area ratio (FAR) calculated in Atherton?

FAR rules are district‑specific. Some districts use a percentage (e.g., 18% in parts of R‑1B) while others use a formula for small lots (see § 17.33.040(C) and Parker formula in § 17.37.040(B)). Basements and some open roofed areas may be excluded per Chapter 17.44. § 17.33.040(C); § 17.37.040(B); § 17.44.040 filefile

What setbacks apply if my lot abuts an R-1 parcel?

Where a project (for example an RM overlay development) abuts an R‑1 parcel, larger R‑1 adjacent setbacks apply — for example 50 ft minimum in some RM contexts — and sidewall height limitations are stricter. See § 17.36.070(C) for the RM‑overlay R‑1 adjacent rules. § 17.36.070(C)

How are height measurements determined in Atherton?

Height measurement methodology and how average natural grade is calculated are set in Chapter 17.42, especially § 17.42.030; height exceptions (chimneys, solar panels, architectural projections) are in § 17.42.040. § 17.42.030–.040 file

Can multifamily housing be built by right in Atherton?

On certain mapped PFS parcels with an RM‑20 or RM‑40 overlay, multifamily housing can be allowed by‑right under the objective standards in § 17.36.070 (density, height, setbacks). Confirm that the parcel is mapped for the overlay and complies with the objective standards. § 17.36.070

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