Local zoning · Los Altos Hills

Los Altos Hills — Overlay Districts

Q: What can I build on an R‑A lot in Los Altos Hills?

Most single‑family residences , accessory structures, and accessory dwelling units are permitted in R‑A ; certain institutional or public uses may require conditional permits. See the permitted uses table and conditional uses in § 10‑1.702 and § 10‑1.703 .

Q: What are Los Altos Hills setback and lot‑size requirements?

Minimum lot size is 43,560 sq ft (1 acre) and each lot must contain a 160‑ft diameter circle ; detailed setback and development area limits are set by Article 5 formulas (see § 10‑1.501 and § 10‑1.502 ). Estate homes (≥ 10,000 sq ft ) have larger setback tables in § 10‑1.508 .

Q: If my project is an "estate home," what extra rules apply?

If a building’s floor area is 10,000 sq ft or greater it meets the estate home definition and must meet the larger front/side/rear setbacks and other special conditions in § 10‑1.508 ; expect discretionary conditions to protect the Town’s rural character.

Q: Where do I check whether my parcel is covered by the Upper Neary Quarry Lands rules?

The Upper Neary Quarry Lands Article references a Figure/Exhibit map that identifies the affected Lots; check the Town’s official zoning map and the Exhibit referred to in § 10‑1.901 (the Exhibit is not in the retrieved text). Verify with the Planning Department.

Overlay Districts under the Los Altos Hills local zoning and planning code, with the controlling citations.

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Last reviewed: July 2, 2026

Overview

Los Altos Hills' Zoning and Site Development Code (Title 10) does not use a standalone "Overlay District" label. Instead, the Town applies targeted, site- or subject-specific regulations through named districts and special articles (for example, Residential‑Agricultural (R‑A), Open Space Reserve (OSR), Upper Neary Quarry Lands, and special rules for Estate homes). Where site‑specific controls are applied, they are implemented as amendments to the zoning map or as separate Articles in Title 10 rather than under a generic "overlay" heading (see § 10‑1.301, § 10‑1.302, § 10‑1.901).

Below is a Los Altos Hills–specific breakdown of the districts and special-area rules that perform the practical role overlays often serve in other jurisdictions, with citations to the controlling code sections and practical guidance for applicants.

Residential‑Agricultural (R‑A)

Purpose: Preserve the Town’s semi‑rural, low‑density hillside character by allowing low‑density residential uses and accessory uses compatible with agriculture and open space. § 10‑1.301 establishes the district.
Typical permitted uses: Single‑family residences, accessory structures, accessory dwelling units (ADUs) (subject to Article 14), agricultural/horticultural uses, and certain public or institutional uses as listed in the R‑A use tables. See § 10‑1.702 for permitted uses and § 10‑1.703 for conditional uses.
Key dimensional standards: Minimum parcel size 43,560 sq ft (1 acre) with the requirement that each lot contain a 160‑ft diameter circle; development area and maximum floor area are calculated by formula and slope/lot factors (Article 5). See § 10‑1.501 and § 10‑1.502.
Where it applies: Townwide default district for unclassified land and the predominant residential district shown on the Town zoning map. See § 10‑1.307 and § 10‑1.302.
Practical notes: ADUs are explicitly authorized and governed by Article 14; ADU provisions supersede other conflicting provisions when applicable — check § 10‑1.1403 and related ADU sections before relying on general R‑A rules. For ADU technical standards see the Building Code and the Town’s ADU article.

(Linking to related topics: the Town’s Zoning & planning overview and Los Altos Hills Zoning give context for R‑A designations; read the Town Development Standards for formula calculations; ADU rules are at Los Altos Hills ADUs.)

Open Space Reserve (OSR)

Purpose: Protect and maintain lands intended for permanent open space, forest preserves, grazing and other low‑impact open uses. § 10‑1.801 establishes OSR primary uses and restrictions.
Typical permitted uses: Agricultural uses (horticulture, grazing), forest preserves, and other open space uses; accessory structures are limited to those necessary for the primary use. See § 10‑1.801 and § 10‑1.802.
Key dimensional standards: Area, coverage, height and setbacks defer to Article 5 standards and lot‑specific formulas (see § 10‑1.803, Article 5 generally).
Where it applies: Specific parcels shown as OSR on the Town’s Zoning Map; lands annexed to the Town default to OSR until rezoned (see § 10‑1.306 and § 10‑1.302).
Practical notes: Many commercial and high‑density uses are expressly prohibited in OSR; confirm a parcel’s map designation before proposing development as the OSR classification is restrictive. See § 10‑1.804 for prohibited uses.

(Link: if your proposal affects parking or setbacks also consult Los Altos Hills Parking and Los Altos Hills Development Standards.)

Upper Neary Quarry Lands (site‑specific / special lands article)

Role: Acts like an area‑specific overlay: the Upper Neary Quarry Lands are regulated through a dedicated Article with bespoke development limits and conservation easement requirements rather than a generic overlay label. See § 10‑1.901 and § 10‑1.902.
Purpose & controls: Limits on dwelling siting (no ridgeline/hilltop siting), height restrictions to preserve views, one dwelling per lot, minimum lot sizes for that area, and required conservation easements to limit subsequent development. See the special conditions summarized in § 10‑1.901 and definitions in § 10‑1.902.
Practical notes: Because these rules are area‑specific and tied to an Exhibit map referenced in the Article, treat them as a de facto overlay for affected parcels; verify the parcel against the Exhibit and zoning map before proposing changes. Verify with the jurisdiction for parcel application.

Estate Homes provisions (special size‑triggered standards)

Function: Additional setbacks and special development rules that apply to very large residences (estate homes) — these are not a map overlay but a use/size‑triggered special standard (Article 5, § 10‑1.508).
Trigger/definition: An estate home is defined as a building with 10,000 sq ft or greater floor area (exclusive of basements) — if a project meets that definition, additional setbacks and other conditions apply. See § 10‑1.508(b)–(c).
Practical notes: Estate‑scale proposals are subject to larger front setbacks (starting at 44 ft and increasing by size) and larger side/rear setbacks; applicants should expect stricter design review and potential conditions that reduce Maximum Development Area or Maximum Floor Area. § 10‑1.508(c) and related conditional permit provisions apply.

(Link to Los Altos Hills Design Review and Los Altos Hills Variances and Exceptions for process context.)

Quick reference table — decision‑relevant standards and permitted uses

District / Special Rule	Most decision‑relevant standards / typical permitted uses	Code Reference
Residential‑Agricultural (R‑A)	Single‑family homes, ADUs (per Article 14); min lot 43,560 sq ft; lot must contain 160‑ft circle; development area and MFA by formula.	§ 10‑1.301, § 10‑1.501, § 10‑1.502, § 10‑1.702, § 10‑1.1403
Open Space Reserve (OSR)	Agriculture/forest preserves/open space; accessory structures limited; area/coverage per Article 5.	§ 10‑1.801 – § 10‑1.804, § 10‑1.803
Upper Neary Quarry Lands (special area)	One primary dwelling per lot; no ridgeline/hilltop siting; conservation easement required for development; development caps tied to R‑A standards.	§ 10‑1.901, § 10‑1.902
Estate homes (size‑triggered standards)	Trigger at 10,000 sq ft; increased front setback 44 ft (and larger with size); side/rear setbacks 33 ft (increasing with size).	§ 10‑1.508(b)–(c)

Checklist

Confirm parcel zoning on the Town zoning map and any Exhibit maps (R‑A vs OSR vs special area) — see § 10‑1.302, § 10‑1.303.
Verify whether the parcel falls inside the Upper Neary Quarry Lands or other site‑specific Article area — consult § 10‑1.901/902 and the Exhibit referenced there.
Calculate Maximum Development Area and Maximum Floor Area per Articles 5 and 2 formulas (see § 10‑1.502 and supporting definitions).
Determine if the proposal is an estate home (≥ 10,000 sq ft) and apply the additional setback rules in § 10‑1.508.
If adding an ADU, follow Article 14 standards and the streamlined ADU process — see § 10‑1.1401–§ 10‑1.1407.
Prepare for design review/site development and possible conditional development permits or variances (Article 10 procedures for appeals/permits) — see § 10‑1.1001–§ 10‑1.1009.
Check parking requirements, landscape screening, and signage requirements where applicable — consult Los Altos Hills Parking, Los Altos Hills Landscaping and Screening and Los Altos Hills Signage.
Confirm building‑code compliance separately (California code) with California Building Standards Code.

Risks & Ambiguities

Issue	Why it matters	What to verify
No explicit "Overlay District" term	Town uses Articles and map annotations instead of a named overlay; legal expectations from overlay practice (e.g., stacking rules) may not directly apply.	Verify whether the parcel is subject to any Article or Exhibit (e.g., Upper Neary Quarry Lands) or map note; check § 10‑1.302 and the Exhibit referenced in the special Article.
Parcel‑specific mapping (Exhibits)	Several special rules are tied to maps or Exhibits incorporated by reference; if your parcel isn’t on the Exhibit, those rules may not apply.	Confirm parcel against the Town zoning map and any Exhibit attachments cited in the code (Zoning Map adoption language § 10‑1.302).
Estate‑home triggers (10,000 sq ft)	Large developments face additional setbacks and stronger discretionary review; failing to detect trigger early can force redesign.	Determine proposed floor area vs. the estate home threshold in § 10‑1.508(b).
ADU rule interactions with other standards	ADU Article may preempt some local constraints, but other site limits (MDA, lot unit factor, conservation easements) still bind.	Use § 10‑1.1403 with Article 5 calculations and check for conservation easement restrictions in § 10‑1.901.
Setback/coverage formulas vary with slope/lot factor	Maximum development area and lot coverage are formulaic and parcel‑specific — incorrect slope or LUF leads to wrong MDA/MFA.	Calculate per § 10‑1.502, confirm slopes in § 10‑1.202 (definitions) and consider professional survey.
Process timing and appeals	Many approvals have multi‑stage review and tight appeal windows (14–21 days) — missing deadlines jeopardizes approvals.	Check appeal and effective date rules in § 10‑1.1008–§ 10‑1.1009.

Plain‑English Summary

Los Altos Hills does not use a generic “overlay district” label; instead the Town applies site‑ or subject‑specific rules through the existing districts and special Articles (for example, rules for Upper Neary Quarry Lands and Estate homes). Start by confirming the parcel’s zoning and any Article/Exhibit that applies (R‑A or OSR), then apply the Article‑specific standards (lot area, MDA/MFA formulas, estate home setbacks, ADU Article 14) before preparing plans and pursuing design review or discretionary permits. Verify parcel results with the Planning Department.

Information Gaps

The code text retrieved does not include any section explicitly titled "Overlay District" or a generic overlay map legend. Not found in retrieved materials.
The exact zoning map Exhibits and graphic maps referenced by the Upper Neary Quarry Lands Article are not included in the retrieved text; the Exhibit locations and parcel boundaries must be checked with the Town’s official zoning map. Verify with the jurisdiction.
Parcel‑specific interpretations (lot unit factor, slope calculations, and whether an application triggers Conditional Development Permit vs ministerial review) are inherently site dependent — Verify with the Planning Department. See § 10‑1.502 and permit procedure sections.

Source References

§ 10‑1.301 (Establishment of districts: R‑A, OSR)
§ 10‑1.302 (Zoning map adoption; how districts and maps are incorporated)
§ 10‑1.501 / § 10‑1.502 (Minimum parcel size; Development Area / MDA formula — Article 5)
§ 10‑1.702 / § 10‑1.703 (Uses and conditional uses in R‑A)
§ 10‑1.801 – § 10‑1.804 (Open Space Reserve District uses and prohibitions)
§ 10‑1.508 (Estate homes: definition and additional setbacks)
§ 10‑1.901 / § 10‑1.902 (Upper Neary Quarry Lands special article)
Article 14 / § 10‑1.1401–§ 10‑1.1407 (Accessory Dwelling Units — Town ADU rules)
§ 10‑1.1001–§ 10‑1.1009 (Applications, appeals, variances and conditional permits — procedural requirements)
Zoning Code source document (Los Altos Hills Zoning and Site Development Code, Title 10, excerpted) — downloaded/compiled text.

(For construction/building code compliance also consult the California Building Standards Code.)

Sources

Retrieved passages

Los Altos Hills Zoning Code (§ 1) High relevance
Los Altos Hills Zoning Code (Article 10) Medium relevance
Los Altos Hills Zoning Code (§ 1) Medium relevance
Los Altos Hills Zoning Code (§ 10-1.1305) Medium relevance
Los Altos Hills Zoning Code (chapter as) Medium relevance
Los Altos Hills Zoning Code (§ 1) Medium relevance
Los Altos Hills Zoning Code (§ 1) Medium relevance
Los Altos Hills Zoning Code (§ 1) Medium relevance
Los Altos Hills Zoning Code (Section 10-1.301) High relevance
Los Altos Hills Zoning Code (Section 66499.37) Medium relevance
Los Altos Hills Zoning Code (§ 10-1.902.) Medium relevance
Los Altos Hills Zoning Code (§ 10-1.704.) Medium relevance
Los Altos Hills Zoning Code (§ 10-1.1311) Medium relevance

Cited sections

Official Los Altos Hills code library

Frequently asked questions

What can I build on an R‑A lot in Los Altos Hills?

Most single‑family residences, accessory structures, and accessory dwelling units are permitted in R‑A; certain institutional or public uses may require conditional permits. See the permitted uses table and conditional uses in § 10‑1.702 and § 10‑1.703.

What are Los Altos Hills setback and lot‑size requirements?

Minimum lot size is 43,560 sq ft (1 acre) and each lot must contain a 160‑ft diameter circle; detailed setback and development area limits are set by Article 5 formulas (see § 10‑1.501 and § 10‑1.502). Estate homes (≥ 10,000 sq ft) have larger setback tables in § 10‑1.508.

Do I need design review in Los Altos Hills?

Many projects require design review, site development permits, or discretionary review depending on size and whether variances/conditional permits are needed; consult the Town’s permit procedure articles and the Design Review page. Permit procedures and appeal timing are in § 10‑1.1001–§ 10‑1.1009.

Are there any overlay‑style areas I need to worry about?

There is no separate "Overlay District" chapter in the retrieved Title 10. Instead, area‑specific rules (for example Upper Neary Quarry Lands, Estate homes) act like overlays by attaching special rules to particular places or project types — see § 10‑1.901/902 and § 10‑1.508. Verify parcel applicability on the Town zoning map.

How do ADU rules interact with R‑A or OSR requirements?

ADUs are permitted under Article 14 and have their own standards; Article 14 is applied in that sequence but ADU approvals do not override other parcel constraints (e.g., conservation easements or MDA formulas). See § 10‑1.1401–§ 10‑1.1407 for ADU standards.

If my project is an "estate home," what extra rules apply?

If a building’s floor area is 10,000 sq ft or greater it meets the estate home definition and must meet the larger front/side/rear setbacks and other special conditions in § 10‑1.508; expect discretionary conditions to protect the Town’s rural character.

Where do I check whether my parcel is covered by the Upper Neary Quarry Lands rules?

The Upper Neary Quarry Lands Article references a Figure/Exhibit map that identifies the affected Lots; check the Town’s official zoning map and the Exhibit referred to in § 10‑1.901 (the Exhibit is not in the retrieved text). Verify with the Planning Department.

Can I get a variance if the overlay‑style rules block my project?

Variances are available under the Town’s variance rules but are discretionary and require findings showing practical difficulty or hardship; see the variance criteria and processing authority in § 10‑1.1007 and related subsections.

Who decides appeals and what's the appeal timing?

Administrative decisions can be appealed to the Planning Commission (typically 14 days for Staff Committee decisions) and to City Council (timing varies); see § 10‑1.1008 and § 10‑1.1009 for appeal deadlines and procedures.

Are map amendments or overlay‑style boundary changes frequent?

Changes to district boundaries are processed as zoning map amendments and must be reflected on the zoning map with ordinance and effective date notations per § 10‑1.304; check recent ordinances and map updates to see current boundaries.

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