Local zoning · Atherton

Atherton — Development Standards

Development Standards 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 Atherton’s zoning-development standards (setbacks, heights, lot coverage, FAR, density) as adopted in Title 17 of the Atherton Municipal Code and related overlay chapters. It focuses only on the zoning-development rules (not building-code, permitting steps, or tenant/housing law). For definitions and process items see the town zoning and land-use pages linked below. Key rules below are grounded in the local ordinance (Title 17) cited by section.

Note: the first time the topics below are naturally mentioned they are linked to related GoCodebook pages for quick cross-reference: setbacks (Atherton Zoning), parking (Atherton Parking), design review (Atherton Design Review), overlay (Atherton Overlay Districts), ADUs (Atherton ADUs), and California Building Standards Code (California Building Standards Code).

District-by-district development standards (decision-focused)

Below are the main residential and public-district standards a project applicant will encounter in Atherton. Each district subsection gives the ordinance purpose, typical permitted uses (high-level), the principal dimensional controls, and where the rules apply. All numeric rules are bolded and grounded to the specific Town code section.

R-1A (Single-Family Residential — base district)

  • Purpose / uses: The R-1A district is the primary single-family residential district; it governs conventional single-family lots and small-lot areas (see also Parker Avenue overlay). The ordinance treats accessory buildings and ADUs under separate chapters. See § 17.32.040 .
  • Key dimensional standards:
    • Maximum height (standard): 30 ft; vertical sidewalls/columns limited to 22 ft. Height increases up to 34 ft (and sidewalls up to 28 ft) may be allowed with increased setbacks or by special structure permit (see criteria) § 17.32.040 .
    • Setbacks: the chapter references setbacks and that greater setbacks permit height increases, but the numerical front/side/rear yard tables for R-1A are contained elsewhere in Title 17 tables and side-yard chapters — verify with the lot-specific table and chapter § 17.32.040 and chapter § 17.38.010 .
    • Lot coverage/FAR: lot coverage regime used elsewhere in the Title (see general lot-coverage language: 40% building coverage, 20% impervious surfaces, 50% total) — apply the specific district chapter and accessory building rules § 17.32.040 and related lot coverage text .
  • Special notes: Dormers and other projections have specific rules tied to sidewall limits § 17.32.040 . ADUs must also meet chapter standards (see § 17.52.040 and the ADU page) .

RM-10 (Multifamily Overlay — Residential Multifamily 10)

  • Purpose / uses: The RM-10 overlay authorizes multifamily development up to 10 units/acre on specified parcels (typically on R-1A and POS parcels listed in the Housing Element); multi‑unit projects meeting these objective standards are by-right (subject to other compliance) § 17.35.010–.020 .
  • Key dimensional standards (development standards in § 17.35.030):
    • Maximum height: 34 ft for main buildings; vertical end walls/sidewalls/columns facing the front setback limited to 28 ft, and 21 ft where the wall faces a side/rear setback line (with additional setback allowance for extra height) § 17.35.030(A) .
    • Minimum front yard: 30 ft (main building). If front‑setback building height exceeds 28 ft, the front yard must increase by 1 ft for each 1 ft of height over 28 ft § 17.35.030(B)(1) .
    • Side yards: tiered numeric table based on lot width (see Table 17.35.030.B.2-1); minimum individual side yards range down to 15 ft for narrow lots, with larger setbacks where adjacent to an R-1 parcel (R-1-adjacent setbacks increase to 25–50 ft depending on lot width) § 17.35.030(B)(2) .
    • Minimum spacing between main buildings on the same lot: 20 ft § 17.35.030(E)(3) .
    • Floor Area Ratio (FAR): 0.45 of lot area; may be increased to 0.55 (0.10 additional) if all resident parking is fully below grade. Habitable basements don’t count toward FAR if parking is fully below grade (see limits and counting rules) § 17.35.030(C) .
    • Lot coverage: 40% building coverage; 20% impervious surfaces (non-building); 50% maximum total § 17.35.030(C) .
  • Site design rules: pedestrian connectivity, streetscape, driveway width (max 26 ft), vision triangle, and landscape screening are required; surface parking may be restricted within setbacks and other access rules apply — see § 17.35.030(E–F) .

RM-20 and RM-40 (Multifamily Overlays with higher height/density allowances)

  • Purpose / uses: Higher-intensity multifamily overlays; apply to parcels listed in the zoning maps and overlay chapter § 17.36.070 .
  • Key dimensional standards:
    • RM-20 maximum height: 34 ft; RM-40 maximum height: 48 ft (with a flat-roof cap of 42 ft or vertical midpoint rules) § 17.36.070(A) .
    • Vertical sidewalls built at the setback line are further limited when adjacent to R-1 parcels (sidewall cap 21 ft for R-1 adjacent situations); if you want more height at the setback you must increase setback by 1 ft for every 1 ft of additional height § 17.36.070(A)(1–3) .
    • General minimum setback from property line: 40 ft (see RM-20/RM-40 setback figures); where adjacent to R-1, R-1-adjacent setback = 50 ft (and may be graduated by lot width) § 17.36.070(B) .
    • Lot coverage and impervious surface caps: the same 40% / 20% / 50% split is stated for overlay and multifamily development § 17.36.070(C) .

POS (Parks and Open Space)

  • Purpose / uses: POS district governs park, recreation, open-space uses — buildings in POS are treated as main buildings (not accessory) § 17.34.040 .
  • Key dimensional standards (Table 17.34.040-1):
    • Maximum height: 34 ft § 17.34.040 .
    • Lot coverage (aggregate maximum): 20% of gross lot area § 17.34.040 .
    • Front and rear yard minimum: 60 ft; side yard: see chapter 17.38 (variable) § 17.34.040 .

PFS (Public Facilities & Schools)

  • Purpose / uses: PFS applies to public facilities and schools; it has special setback/yard rules to buffer residential uses § 17.36.040 .
  • Key dimensional standards:
    • Maximum height: 34 ft (standard) and special setback/height transitions where adjacent to residences § 17.36.040 (table and notes) .
    • Front yard minimum: 60 ft when building height ≤ 22 ft (in some PFS locations); when building height > 22 ft front/rear setbacks may increase to 75 ft per the table notes § 17.36.040 .
    • Side- and rear-yard minimums also referenced to chapter 17.38 or fixed distances in the PFS table; special rules apply for school adjacencies § 17.36.040 .

Parker Avenue Overlay (P)

  • Purpose / relationship: The Parker Avenue (P) overlay modifies the R-1A standards for a cluster of small lots along Parker Avenue. When the overlay applies, its standards govern in conflicts with R-1A § 17.37.010–.020 .
  • Key dimensional changes (development modifications in § 17.37.040):
    • Standard maximum building height: 28 ft (vertical sidewalls/columns may not exceed 20 ft) § 17.37.040(A) .
    • Maximum FAR is set by formula: floor area = (lot size in sq ft × 0.165) + 1,500 sq ft; second-story floor area above ground-floor limit also capped (1100–1132 sq ft depending on the rule) § 17.37.040(B) .
    • Front yard for single-story portion ≤15 ft tall: 23 ft 3 in § 17.37.040(C) .

Quick reference table — most decision-relevant standards

District Max height Min front setback Max lot coverage (building) FAR / Floor area Key permitted uses Code Reference
R-1A 30 ft (std); up to 34 ft w/conditions See district tables / chapter 17.38 See Title 17 general rule (building 40%) Not a flat FAR standard; area rules & limits apply Single-family, accessory buildings, ADUs (per ch. 17.52) § 17.32.040
RM-10 (multifamily overlay) 34 ft 30 ft front minimum Building 40%; impervious 20%; total 50% 0.45 (up to 0.55 if resident parking fully below grade) Multifamily by-right when standards met (≤10 u/acre) § 17.35.030
RM-20 34 ft 40 ft general setbacks; larger if R-1-adjacent Building 40% See overlay chapter Multifamily § 17.36.070
RM-40 48 ft (max; flat roof cap 42 ft) 40 ft general setbacks; larger if R-1-adjacent Building 40% See overlay chapter Multifamily (higher intensity) § 17.36.070
POS 34 ft 60 ft front & rear Aggregate lot coverage 20% Not generally a conventional FAR Parks, open space, civic § 17.34.040
PFS 34 ft (standard) 60 ft / 75 ft depending on height & adjacencies Building 40% (notes) Special rules; see table Schools, public facilities § 17.36.040
Parker (P) overlay 28 ft standard; vertical sidewalls 20 ft 23 ft 3 in (single‑story ≤15 ft) FAR governed by formula (lot × 0.165) + 1,500 sq ft Formula-based Modified single-family rules for Parker Ave. § 17.37.040

(See the cited chapters for full tables and graphics; many setback and side‑yard minima are presented as tables keyed to lot width and adjacency status — consult the exact table for parcel-specific numbers) § 17.35.030(B), § 17.36.070(B), chapter 17.38 .

Measurement rules, exceptions, and related standards

  • How height is measured: Height measurement rules and special provisions (basements, sidewall measurement, benchmarks, certifications) are in § 17.42.030 (including requirement for engineer/surveyor certification at roof framing and placement of a non-removable benchmark) and exceptions in § 17.42.040 (chimneys, solar panels, towers, minor projections) .
  • Sidewall/adjacent R‑1 transitions: Where a multifamily or overlay building abuts an R-1 parcel, stricter sidewall height and setback transitions apply (e.g., R-1-adjacent setback min: 50 ft in many cases; sidewall caps 21 ft adjacent to R-1) § 17.36.070 .
  • Lot coverage and impervious surfaces: A recurring townwide formulation limits building coverage to 40%, impervious surfaces to 20%, and total to 50% unless a district table states otherwise (common language at § 17.35.030(C) and elsewhere) .
  • Accessory Dwelling Units (ADUs): ADU standards and where ADUs do or do not count toward density are in chapter 17.52 (development standards summarized in § 17.52.040). ADUs generally must meet ADU-specific setbacks, height, and number rules; consult the ADU chapter and the town ADU guidance page for state-law interactions § 17.52.040 .
  • SB 9 / Urban lot split impacts: Objective standards for parcels created under the SB 9/urban lot split chapter (e.g., maximum units, height limits, floor area caps for SB 9 units) are in § 17.53.050. For example, two units per parcel result is the maximum and specific height/FAR rules apply depending on whether original setbacks are met § 17.53.050 .
  • Site design & circulation: Driveway maximum width 26 ft, driveway vision triangles (10 ft x 10 ft) with a 3 ft max obstruction height, pedestrian/pathway requirements, and parking location rules are present across overlay and development standards chapters; see § 17.35.030(E) and § 17.32.040(E) for specifics § 17.35.030(E) . If your proposal triggers a VMT analysis, the code references C/CAG tools for high‑VMT areas § 17.35.030 .

Checklist (what an applicant must satisfy to demonstrate compliance with Atherton development standards)

  • Confirm property zoning and any overlays (RM-10, RM-20, RM-40, POS, PFS, Parker (P)) and applicable tables § 17.35.010–.020; § 17.36.070; § 17.34.040 .
  • Demonstrate conformance with district height limits and height‑measurement rules; include a surveyor/civil engineer certification at roof framing and benchmark placement as required § 17.42.030 .
  • Show required setbacks and side‑yard calculations (include any increased R‑1 adjacent setbacks) using the exact table rows keyed to lot width § 17.35.030(B); chapter 17.38 .
  • Provide FAR/floor‑area calculations and show whether parking is below grade to claim any FAR bonus § 17.35.030(C) .
  • Submit lot coverage and impervious-surface calculations (building 40%, impervious 20%, total 50% unless district table says otherwise) § 17.35.030(C) .
  • Include site-design sheets: pedestrian path connectivity, driveway plan (≤ 26 ft), vision triangle control, and landscape screening consistent with chapter 17.50 § 17.35.030(E–F) .
  • For ADUs, follow § 17.52.040 development standards and confirm ADU setbacks/height per the chapter § 17.52.040 .
  • If proposing increased heights or other exceptions, prepare a Special Structure Permit or variance submittal tied to the specific approval authority and findings (see variances/exception rules in title) Verify with the jurisdiction.

Risks & Ambiguities

Issue Why it matters What to verify
Incomplete R-1A numeric setback table in retrieved snippets Lot‑by‑lot setback obligations for R-1A are implemented via tables; snippet set includes height rules but not every numeric front/side/rear entry Confirm the precise R‑1A front/side/rear yard table in Title 17 (chapter 17.32 and 17.38) and with planning staff Verify with the jurisdiction
R-1‑adjacent rules vs. RM overlays RM overlays frequently require much larger setbacks and lower sidewall heights where abutting R-1 — this can dramatically reduce buildable envelope Check the applicable overlay figure/table for your lot width and whether the adjacent parcel has RM overlay or active multifamily applications § 17.36.070
FAR counting (basements, below-grade parking) The ordinance excludes certain basement/parking from FAR but has conditions (e.g., all resident parking must be below grade) Confirm how proposed subterranean/garage/parking areas will be counted and provide a cross‑section; check § 17.35.030(C)
ADU state-law conflicts State ADU law limits what local rules can require (size, setbacks, parking) and may override local provisions Cross-check local ADU chapter 17.52 with state ADU law; see the Atherton ADU page and California ADU law page § 17.52.040
Parcel‑specific graphics/tables missing from text snippets Several ordinance figures and tables (setback graphics, lot-width keyed tables) are illustrated graphics in Title 17 and were omitted in the snippets Pull the full Title 17 PDF / table images from the Town code or confirm with Planning counter for the precise table row for your parcel Verify with the jurisdiction

Plain-English Summary

Atherton’s Title 17 sets clear dimensional ceilings: single-family lots under R-1A are generally limited to about 30 ft tall (with controlled options to reach 34 ft); multifamily overlays (RM‑10/20/40) allow taller buildings (up to 34 ft or 48 ft) but require much larger setbacks and stricter sidewall transitions where they touch R‑1 lots; building coverage is generally capped at 40% with impervious surfaces 20% and 50% total; multifamily FAR is typically 0.45 (up to 0.55 with fully below‑grade resident parking) — all of which are codified in Title 17 tables and figures that must be used to calculate a proposal’s buildable envelope (see cited sections) .

Source References

  • Atherton Municipal Code, Title 17 — Chapter 17.35 (Multifamily Overlay RM-10: Development Standards: height, setbacks, FAR, lot coverage) § 17.35.030 .
  • Atherton Municipal Code, Title 17 — Chapter 17.36 / 17.36.070 (RM‑20 / RM‑40 overlay development standards: heights, sidewall limits, R‑1 transitions) § 17.36.070 .
  • Atherton Municipal Code, Title 17 — Chapter 17.32 (R‑1A development standards — heights, dormers, general development direction) § 17.32.040 .
  • Atherton Municipal Code, Title 17 — Chapter 17.34 (POS District development standards; Table 17.34.040-1) § 17.34.040 .
  • Atherton Municipal Code, Title 17 — PFS District standards (table & notes) § 17.36.040 .
  • Atherton Municipal Code, Title 17 — Parker Avenue Overlay (development modifications, FAR formula, front setbacks) § 17.37.040 .
  • Atherton Municipal Code, Title 17 — Height measurement and exceptions § 17.42.030 and § 17.42.040 (benchmark certification, measurement rules, exceptions) .
  • Atherton Municipal Code, Title 17 — Lot coverage and site-design language repeated across overlay chapters (building 40% / impervious 20% / total 50%) (e.g., § 17.35.030(C); § 17.36.070(C)) .
  • Atherton Municipal Code, Title 17 — ADU development standards § 17.52.040 (accessory dwelling requirements) .
  • Atherton Municipal Code, Title 17 — SB 9 / Urban lot split objective standards § 17.53.050 (unit counts, height and floor-area limits for SB 9 units) .
  • For cross-topic pages on GoCodebook linked above: Atherton zoning & planning overview, overlays, parking, design review, ADUs and the California Building Standards Code are linked in the page body to the GoCodebook menu (internal pages).

Sources

Retrieved passages

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

Cited sections

Frequently asked questions

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

You can build single‑family residential development subject to the R‑1A chapter limits: standard 30 ft maximum height (vertical sidewalls 22 ft) with limited options to increase up to 34 ft under the rules in § 17.32.040. Parcel-specific setback and side‑yard tables control the buildable envelope; accessory buildings and ADUs are governed by separate chapters (ADUs: § 17.52.040) .

What are Atherton setback requirements for multifamily overlays?

Multifamily overlays set specific setbacks: RM‑10 generally requires a 30 ft front yard and side/rear setbacks by table keyed to lot width (with R‑1‑adjacent setbacks significantly larger), while RM‑20/RM‑40 use 40 ft general setbacks and larger R‑1‑adjacent buffers; see § 17.35.030(B) and § 17.36.070(B) for the exact tables and graduated values .

Do I need design review for a new house or addition in Atherton?

Design review may be required depending on district, overlay, and the project’s scope; the code sets objective dimensional standards (height, setbacks, FAR) but discretionary actions (e.g., special structure permits, variances, or projects not meeting objective standards) can trigger design or discretionary review. Check the local design‑review procedures and the project’s conformity to Title 17 standards (verify with planning staff) § 17.32.040 .

How is building height measured in Atherton?

Height is measured per § 17.42.030 with detailed rules for basements, sidewall measurement, and required surveyor/engineering certification at roof framing; minor projections and solar panels have specified exceptions in § 17.42.040 .

What are the lot‑coverage and FAR limits I must use?

Townwide development language caps building coverage at 40%, impervious surfaces at 20%, and total coverage at 50% unless a district table specifies otherwise. For multifamily in the RM‑10 overlay, FAR is 0.45, up to 0.55 if all resident parking is below grade § 17.35.030(C) .

Where can I put parking and how wide can a driveway be?

Driveway maximum width is 26 ft and driveways must meet Fire Marshal rules. Multifamily site rules commonly prohibit surface parking within required setbacks and require vision triangles (10 ft x 10 ft) with max vegetation/structure heights of 3 ft in that triangle § 17.35.030(E) .

Can I increase height if I increase setbacks?

Yes — several districts allow increased height in exchange for increased setbacks (many codes use a ratio such as 1 ft additional setback for 1 ft of added height or other ratios, or require a Special Structure Permit). See the R‑1A height‑setback tradeoffs § 17.32.040 and RM overlay figures and ratios in § 17.35.030(A) and § 17.36.070(A) .

Do ADUs count toward FAR or density in Atherton?

ADUs and JADUs are considered accessory and generally do not count toward allowable lot density for the primary parcel; ADUs must comply with chapter 17.52 standards which also set building/height/setback rules for ADUs § 17.52.040 .

What if my parcel was created under SB 9 or an urban lot split?

Parcels resulting from an urban lot split have objective standards in § 17.53.050: a maximum of two units per resulting parcel (including ADUs/JADUs), and specific fallback rules for height, setbacks and floor area if the underlying district setbacks are not met § 17.53.050 .

Where can I confirm parcel‑specific tables and graphics (lot width rows)?

Many of Title 17’s setback and side‑yard minima are shown in tables keyed to lot width or illustrated figures (these were omitted from text snippets). Always pull the full Title 17 tables/figures for your parcel or verify with planning staff; see the cited chapters for the authoritative tables § 17.35.030(B); chapter 17.38 .

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