Local zoning · Atherton

Atherton — Overlay Districts

Q: What overlay districts exist in Atherton?

Atherton's Title 17 identifies the Parker Avenue Overlay (P) , Multifamily Overlay (RM‑10) , and Multifamily Overlay (RM‑20/40) ; the overlays and their mapping are included by reference to the zoning maps ( § 17.30.080 ) .

Q: Can I build multifamily housing in R‑1A if my parcel has RM‑10?

Yes — the RM‑10 overlay authorizes multifamily development up to 10 units/acre on identified parcels and provides objective design and dimensional standards; the parcel must meet the overlay's eligibility (min 0.5 acre and at least 5 units , exclusive of ADUs) to use these standards ( § 17.35.020; § 17.35.030 ) .

Q: What are the height and setback limits in RM‑20 / RM‑40?

RM‑20 main buildings max 34 ft ; RM‑40 main buildings max 48 ft with midpoint/flat‑roof caveats (some roof measurements capped at 42 ft ); general setbacks are 40 ft from property lines and 50 ft where adjacent to an R‑1 parcel; height‑to‑setback increase ratios apply when buildings exceed certain heights ( § 17.36.070 ) .

Q: Do ADU parking exceptions apply in overlay developments?

ADU parking exceptions and rules are in chapter 17.52 ; ADUs may be exempt from separate parking in several circumstances listed in § 17.52 (e.g., transit proximity, historic districts, conversion of garage) — check the ADU chapter and apply overlay rules where they intersect ( § 17.52 ) .

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

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Last reviewed: July 3, 2026

Overview

Atherton's zoning title establishes specific overlay districts that modify uses and development standards applied over underlying base zones. The Town currently recognizes the Parker Avenue Overlay (P), Multifamily Overlay (RM-10), and Multifamily Overlay (RM-20/40); the overlay program and the maps that show where overlays apply are part of the Town's Title 17 zoning rules (§ 17.30.080) . Overlays either add permitted uses (e.g., multifamily where the base is single‑family) or change dimensional rules (height, FAR, setbacks) for the parcels identified on the zoning map (maps are included by reference) (§ 17.30.080) .

Note: this page covers only what Title 17 says about overlay districts (zoning/land‑use) — building code, housing law, and permitting procedures live in other chapters/pages.

Key overlays at a glance (decision‑relevant table)

Overlay (short)	Primary purpose / where it applies	Most decision‑relevant standards / permitted uses	Code reference
Parker Avenue (P)	Allow adapted single‑family development on small lots in the R‑1A area that front the wide Parker Ave right‑of‑way	Height max 28 ft; vertical sidewalls ≤ 20 ft; FAR = (lot sq ft × 0.165) + 1,500 sq ft; 2nd‑floor cap 1,132 sq ft; single‑story front setback 23 ft 3 in	§ 17.37.010, § 17.37.020, § 17.37.040
Multifamily Overlay (RM‑10)	Permit multifamily up to 10 units/acre on identified R‑1A/POS parcels; objective standards to allow by‑right if met	Min lot 0.5 acre and min 5 units (excl. ADUs); Height max 34 ft; lot coverage 40% / impervious 20% / total 50%; setbacks, sidewall & façade controls	§ 17.35.010, § 17.35.020, § 17.35.030
Multifamily Overlay (RM‑20 / RM‑40)	Allows denser multifamily on PFS parcels (RM‑20 up to 20 u/acre, RM‑40 up to 40 u/acre on Menlo College parcels)	RM‑20 min 12 u/acre; RM‑40 min 24 u/acre; RM‑20 max height 34 ft, RM‑40 max 48 ft (flat roof/midpoint caveats); general setbacks 40 ft; R‑1 adjacent setbacks 50 ft; detailed sidewall limits	§ 17.36.070

District‑by‑district detail

Parker Avenue Overlay District (P)

Purpose / where it applies: The Parker Avenue Overlay (P) is applied over R‑1A lots that are significantly less than one acre and front a 70‑ft public right‑of‑way; the overlay is intended to adapt R‑1A rules for this cluster of small lots (§ 17.37.010; § 17.37.020) .
Typical permitted uses: Single‑family dwellings and those R‑1A uses allowed by the base district unless otherwise modified by the overlay; the overlay is designed to work in combination with R‑1A rules — where the overlay and base conflict, the overlay controls (§ 17.37.010) .
Key dimensional standards (practical highlights):
- Maximum height for main buildings: 28 ft; vertical sidewalls/columns may not exceed 20 ft (§ 17.37.040(A)) .
- FAR / floor area: Floor area = (lot area × 0.165) + 1,500 sq ft; upper‑floor cap 1,132 sq ft (§ 17.37.040(B)) .
- Front setback for single‑story portion (≤ 15 ft tall): 23 ft 3 in (§ 17.37.040(C)) .
Practical guidance: If your parcel is within the P overlay, expect larger allowed floor area than base R‑1A but stricter sidewall vertical limits; always verify overlay mapping and whether your lot meets the "front on the 70‑ft right‑of‑way" criterion (maps are included by reference) (§ 17.30.080) .

Multifamily Overlay (RM‑10) (residential multifamily 10)

Purpose / where it applies: The RM‑10 overlay establishes objective standards to allow multifamily development up to 10 units/acre on specific parcels (identified on the zoning map and in the Housing Element) including some parcels zoned R‑1A or POS (§ 17.35.010; § 17.35.020) .
Typical permitted uses: Multifamily residential is permitted on RM‑10 parcels (and some POS parcels as noted); certain housing types and low‑barrier uses are specifically addressed by state law references in the overlay notes (§ 17.35.020; related notes) .
Key dimensional standards:
- Minimum lot area to apply RM‑10 standards: 0.5 acre and a development must include at least 5 residential units (exclusive of ADUs) unless parcel is POS (exempt) (§ 17.35.020) .
- Height: main buildings max 34 ft; control on vertical sidewalls (front vs. side/rear) and ratio setbacks when exceeding sidewall limits (see § 17.35.030(A)) .
- Setbacks & lot coverage: Front yard 30 ft minimum (with height‑to‑setback ratios); lot coverage 40% building / 20% impervious / 50% total aggregate where applicable (§ 17.35.030(B)(1); § 17.35.030(D)) .
- Site design, vehicle access, façade length, landscape screening, solid fencing along side/rear, minimum spacing between main buildings (20 ft) are detailed in § 17.35.030(E) and related subsections (objective standards) .
Practical guidance: Multifamily projects that meet the objective RM‑10 standards are eligible for by‑right consideration (still may need related permits like grading, utility connections, lot redesignation, or variances if you request departures) (§ 17.35.030) .

Multifamily Overlay (RM‑20 / RM‑40) (on PFS parcels)

Purpose / where it applies: RM‑20 and RM‑40 are overlays applied to portions of parcels zoned PFS (Public Facilities & Schools) where the Town has identified sites appropriate for higher multifamily densities; RM‑20 permits up to 20 u/ac, RM‑40 permits up to 40 u/ac on certain Menlo College areas (§ 17.36.070) .
Typical permitted uses: Multifamily residential uses as described in the RM‑20 / RM‑40 chapter, subject to the RM overlay standards and PFS development rules; some PFS parcels may be conditioned by school master plans or special conditions (§ 17.36.030; § 17.36.050) .
Key dimensional standards:
- Density: RM‑20 up to 20 units/acre (min 12 u/ac for RM‑20); RM‑40 up to 40 units/acre (min 24 u/ac for RM‑40) (§ 17.36.070) .
- Heights: RM‑20 main building max 34 ft; RM‑40 main building max 48 ft, with a midpoint/flat‑roof caveat capping some measures at 42 ft depending on roof type (§ 17.36.070(A)) .
- Setbacks: General property line setback 40 ft; where adjacent to R‑1 parcels the minimum setback is 50 ft; height increases at setbacks require proportional setback increases by specified ratios (§ 17.36.070(B)) .
- Sidewall limits: vertical sidewalls limits for side and front orientations, and reduced heights when facing adjacent R‑1 parcels (e.g., 21 ft facing R‑1) (§ 17.36.070(A)(1)(c)) .
Parking and site‑design companions: RM‑20/40 sit within the broader PFS development framework which contains parking, bicycle parking, underground parking incentives, driveway/vision triangle rules, and VMT analysis requirements for high‑VMT sites — see PFS parking rules (§ 17.36.040 and PFS parking subsections) .
Practical guidance: RM‑20/40 standards are prescriptive and extensive (façade design, screening, lighting, trash enclosures, underground parking incentives). Because RM‑20/40 is tied to specific PFS parcels/map, always confirm the parcel's overlay mapping and whether conversions/aggregate parcel treatments are allowed for contiguous PFS parcels (§ 17.36.070) .

Checklist — what an applicant must satisfy (preliminary)

Confirm the parcel carries the overlay designation on the Town zoning map (maps are included by reference) (§ 17.30.080) . Verify with the Town Planner.
Demonstrate compliance with the overlay's objective development standards (height, setbacks, FAR/area formulas, lot coverage, sidewall rules) — e.g., § 17.37.040 for Parker (P), § 17.35.030 for RM‑10, § 17.36.070 for RM‑20/40 — and include site plans that show measured heights and setbacks using the Town's measurement rules (§ 17.42.030) .
Provide any minimum lot/unit calculations required by the overlay (e.g., RM‑10: min 0.5 acre and 5 units excl. ADUs; RM‑20/RM‑40 density minima) (§ 17.35.020; § 17.36.070) .
For multifamily overlays, include parking and bicycle parking that meets the PFS/multifamily parking standards (including underground parking incentives where proposed) — see PFS parking rules and bicycle parking minimums (§ 17.36.040; parking subsections) and consult the Town's parking page for procedural details .
If proposing ADUs in combination with an overlay project, follow the ADU chapter standards (chapter 17.52) and ADU parking exceptions; see § 17.52 and the Town's ADUs guidance .
Prepare to meet site design standards required by the overlay (landscape screening, façade composition, trash enclosures, lighting, privacy windows) — detailed in § 17.35.030 and § 17.36.070 .
If your proposal requests deviations (variances, special structure permits, lot redesignations), follow the Town’s discretionary procedures (planning commission / city council approval routes) — see the permit approval authority and process in chapter 17.06 and the specific permit chapters (Table 17.06.070‑1) .

Risks & Ambiguities

Issue	Why it matters	What to verify
Overlay map boundaries are not in the code text	Title 17 states overlays are shown on maps included by reference; the printed code chapters do not contain a property‑by‑parcel list	Confirm parcel overlay status with the Town Planner and request the official zoning map (verify § 17.30.080)
Conflicts between base district and overlay standards	The overlay may expressly control any conflict, but application depends on precise language and project details	Confirm the applicable controlling subsection (e.g., § 17.37.010 says overlay controls for Parker) and get a written zoning determination from the Town Planner for ambiguous cases
Parcel‑specific minimums (lot size / min units) for RM overlays	RM‑10 and RM‑20/40 include minimum lot and unit thresholds which determine eligibility for overlay standards	Verify whether your parcel meets RM‑10 min 0.5 acre & 5 units (exclusive of ADUs) § 17.35.020 or RM‑20/40 minima in § 17.36.070; if not, overlay standards may not apply
Parking standard applicability (PFS vs. RM overlays vs ADUs)	Parking rules vary by district (ADU exceptions, PFS maxima, underground incentives) and affect feasibility	Check the applicable parking subsection: PFS/multifamily parking rules and ADU parking exceptions (§ 17.36.040, parking subsections; § 17.52 ADU rules)
VMT / CEQA‑adjacent requirements	Title 17 references VMT analyses for high‑VMT areas for some multifamily/PFS projects	If your site is in a high‑VMT area, prepare a VMT analysis per the code's requirement and C/CAG tools as noted in the parking/VMT subsections (§ 17.36.?? / parking subsections) — verify with the Town which specific section applies and whether an analysis is required

Plain‑English Summary

Atherton’s overlays are targeted zoning layers that either allow multifamily housing on specific parcels (RM‑10, RM‑20/RM‑40) or tailor single‑family rules for a local neighborhood (Parker Avenue P). Each overlay has its own objective development rules (height, setbacks, density, FAR formulas, parking and design rules) that must be met to use the overlay; confirm your parcel’s overlay status on the Town zoning map and follow the cited overlay sections when preparing plans (§ 17.30.080; § 17.37.040; § 17.35.030; § 17.36.070) .

Source References

Definition and list of overlay districts: § 17.30.080 .
Parker Avenue Overlay (P): § 17.37.010; § 17.37.020; § 17.37.040 (development standard modifications including height, FAR, setback) .
Multifamily Overlay (RM‑10): § 17.35.010; § 17.35.020; § 17.35.030 (purpose, applicability, objective standards, lot coverage, setbacks, site design) .
Multifamily Overlay (RM‑20 / RM‑40) on PFS: § 17.36.070 (density, height, setbacks, sidewall rules) and PFS development standards § 17.36.040 (parking, lot coverage context) .
Parking, bicycle parking, underground parking incentives and VMT guidance (PFS/multifamily related): parking subsections in the PFS / multifamily development standards (see parking subsections in Chapter 17.36 / 17.35) (parking subsections) .
ADU rules referenced by overlays: Chapter 17.52 (Accessory Dwelling Units) — ADU parking exceptions noted in the ADU chapter; Town ADU guidance page linked for procedure ADUs .
Administration and permit authority (how overlays interact with permitting): Chapter 17.06 (Approval authority, application processing) .

(Official text is in the Town of Atherton Title 17 zoning code as retrieved in the uploaded files; for parcel‑specific verification, request the Town zoning map and a zoning determination from the Town Planner — the code makes the maps "included by reference" § 17.30.080) .

Sources

Retrieved passages

Atherton Zoning Code (§ 4) High relevance
Atherton Zoning Code (Title 17) High relevance
Atherton Zoning Code (§ 1) High relevance
Atherton Zoning Code (Section 65651) High relevance
Atherton Zoning Code (Title 17) High relevance
Atherton Zoning Code (§ 1) High relevance
Atherton Zoning Code (Section 65915.) High relevance
Atherton Zoning Code (§ 4) High relevance
Atherton Zoning Code (Title 17) High relevance
Atherton Zoning Code (Title 17) Medium relevance
Atherton Zoning Code (chapter establishes) Medium relevance
Atherton Zoning Code (Title 17) Medium relevance
Atherton Zoning Code (Title 17) Medium relevance
Atherton Zoning Code (Title 17) Medium relevance
Atherton Zoning Code (Title 17) Medium relevance
Atherton Zoning Code (Title 17) High relevance
Atherton Zoning Code (Title 17) Medium relevance
CBC § 17.40.040 (section 17.40.040) Medium relevance
Atherton Zoning Code (§ 1) Medium relevance
Atherton Zoning Code (Title 17) Medium relevance

Cited sections

Official Atherton code library

Frequently asked questions

What overlay districts exist in Atherton?

Atherton's Title 17 identifies the Parker Avenue Overlay (P), Multifamily Overlay (RM‑10), and Multifamily Overlay (RM‑20/40); the overlays and their mapping are included by reference to the zoning maps (§ 17.30.080) .

What does the Parker Avenue Overlay let me build that R‑1A does not?

On eligible Parker Ave parcels the overlay allows more total floor area and more second‑story area than base R‑1A but caps vertical sidewalls at 20 ft and the main building at 28 ft; FAR is set by the formula (lot × 0.165) + 1,500 sq ft and the single‑story front setback is 23 ft 3 in (§ 17.37.040) .

Can I build multifamily housing in R‑1A if my parcel has RM‑10?

Yes — the RM‑10 overlay authorizes multifamily development up to 10 units/acre on identified parcels and provides objective design and dimensional standards; the parcel must meet the overlay's eligibility (min 0.5 acre and at least 5 units, exclusive of ADUs) to use these standards (§ 17.35.020; § 17.35.030) .

What are the height and setback limits in RM‑20 / RM‑40?

RM‑20 main buildings max 34 ft; RM‑40 main buildings max 48 ft with midpoint/flat‑roof caveats (some roof measurements capped at 42 ft); general setbacks are 40 ft from property lines and 50 ft where adjacent to an R‑1 parcel; height‑to‑setback increase ratios apply when buildings exceed certain heights (§ 17.36.070) .

Are parking requirements different in the PFS/multifamily overlays?

Yes — PFS/multifamily chapters include specific vehicle and bicycle parking rules (resident parking rates, guest parking rates, underground parking incentives, and screening requirements). Some PFS rules also set a cap on total resident+guest parking unless underground parking is provided; consult the overlay chapter subsections for exact numbers (parking subsections in Chapter 17.36 / 17.35) .

Do ADU parking exceptions apply in overlay developments?

ADU parking exceptions and rules are in chapter 17.52; ADUs may be exempt from separate parking in several circumstances listed in § 17.52 (e.g., transit proximity, historic districts, conversion of garage) — check the ADU chapter and apply overlay rules where they intersect (§ 17.52) .

If my project meets RM‑10 objective standards, is it discretionary?

If a proposed multifamily development complies with the RM‑10 objective standards it is considered by‑right under the overlay; however other actions tied to the project (lot redesignation, variances, special structure permits) may still be discretionary and require additional approvals (§ 17.35.030) .

Where do I confirm whether my parcel is within an overlay?

Title 17 states overlay district locations are shown on maps "included by reference" — the code text itself does not list parcel IDs. You must confirm overlay status with the Town Planner and request the official zoning/overlay map (§ 17.30.080) .

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