Los Altos Hills — Development Standards

Last reviewed: July 2, 2026

Overview

This page summarizes the Los Altos Hills zoning and site development standards that control setbacks, height, lot coverage (development area), floor area (maximum floor area / MFA), and related rules for residential and open-space districts. It is grounded in the Town Zoning and Site Development chapters (Title 10) and highlights the district-level rules you will actually use when planning a project. For procedural and design-review steps see the Town's Los Altos Hills Design Review guidance; for parking requirements see Los Altos Hills Parking.

Residential‑Agricultural (R‑A)

Purpose and typical uses

• The R‑A district is the Town's primary residential category allowing primary dwellings, agriculture, limited institutional uses and accessory uses subject to the Town's design guidance. See permitted uses list (§ 10-1.701) .

Key dimensional and development standards (what an applicant must calculate)

• Minimum parcel size: 43,560 sq ft (1 acre) as a general minimum; exceptions for parcels created prior to 1980 with LUF ≥ 0.5 (§ 10-1.501) .
• Development area (Lot Coverage / MDA): Formula-based; for S ≤ 10%: MDA = LUF × 15,000 sq ft; for S ≥ 30%: MDA = LUF × 7,500 sq ft (intermediate slope formula applies between) (§ 10-1.502) .
• Floor area (MFA / allowed floor area): Formula links MFA to LUF and average slope (for S ≤ 10%: MFA = LUF × 6,000 sq ft; S ≥ 30% uses different base) and a minimum MFA of 5,000 sq ft except where lowered by Conditional Development Permit rules (§ 10-1.503) .
• Height: Base maximum 27 ft structure height. Primary dwellings may rise above 27 ft up to 32 ft if setbacks are increased per the increment rules; absolute maximum roof/top point is 35 ft (special height limit) (§ 10-1.504) .
• Setbacks: Structural setback rules (front, side, rear) and measurement rules are in Article 5; typical front setback measured from the nearest street/right‑of‑way is 40 ft from that line when applicable and 30 ft in other instances — see the precise definitions in § 10-1.505 (§ 10-1.505) .
• Off‑street parking: Each primary dwelling must provide surfaced off‑street parking for a minimum of four cars (at least two covered for new primary dwellings); parking dimensions and access requirements in § 10-1.601 — see Los Altos Hills Parking for municipal practice details (§ 10-1.601) .
• Variances and who decides: Minor MDA/MFA/setback exceptions handled by Staff Committee; larger encroachments or any height envelope exceedance (to go above 27 ft or the 35 ft special limit) go to the Planning Commission (§ 10-1.1007) .
• Conditional Development Permit triggers: Lots with Lot Unit Factor (LUF) ≤ 0.50, significant geologic/noise setbacks, or other constraints require a Conditional Development Permit (§ 10-1.1007(3)) .

Practical guidance

• Run the LUF / slope calculations first — they control both MDA and MFA (§ 10-1.502, § 10-1.503) .
• Expect stricter site‑specific setbacks or lower allowable floor area where the Planning Commission finds high visibility or sensitivity (§ 10-1.505, § 10-1.503) .

Open Space Reserve (OSR)

Purpose and typical uses

• The OSR district preserves agricultural, forest and open‑space uses; only accessory structures necessary to those uses are allowed (§ 10-1.801–802) .

Standards

• Area/coverage/height/setback limitations for OSR defer to Article 5 general provisions (development area, floor area and height formulae) — see § 10-1.803 referencing Article 5 (§ 10-1.803) .
• Prohibited commercial uses (e.g., commercial cannabis) are listed in § 10-1.804 (§ 10-1.804) .

Practical guidance

• Where OSR parcels are proposed for limited development, apply the same MDA/MFA and height rules but expect stricter interpretation to preserve open character (§ 10-1.803, § 10-1.504) .

Estate Homes (special category under Article 5 / § 10‑1.508)

Purpose and when it applies

• Estate home rules apply where a single building totals 10,000 sq ft or more; they add special setback and height controls intended to protect the Town's rural character (§ 10-1.508) .

Key points

• Additional setbacks for estate homes: front setback 44 ft + 4 ft per 2,000 sq ft over 10,000 (cap 60 ft); side/rear 33 ft + 3 ft per 2,000 sq ft (cap 45 ft) (§ 10-1.508) .
• Estate homes may reach 32 ft if the increased setback formula is satisfied; absolute maximum 35 ft (§ 10-1.508, § 10-1.504) .

Accessory Dwelling Units (ADUs) — Article 14

Where allowed and principal limits

• ADUs are permitted on all residentially zoned properties with a single‑family dwelling; Article 14 sets the local objective standards while conforming to State ADU law (§ 10-1.1401–1403) .

Important numeric controls

• Detached ADU: base maximum height 1 story / 16 ft; incentives can increase to 19 ft and 1,200 sq ft if a 30 ft side/rear setback and an extra parking space are provided (§ 10-1.1403, § 10-1.1407) .
• Setbacks for ADUs: front — 40 ft from the street/right‑of‑way; side/rear — at least 4 ft (30 ft encouraged to qualify for incentives) (§ 10-1.1403(e)) .
• Parking: ADU parking is governed by Article 14 and has several exemptions tied to transit proximity, conversions, or demolition of existing garage — see § 10-1.1403(g) and the Town ADU article; ADU review is ministerial and complies with the California Building Standards Code for building safety (§ 10-1.1403, § 10-1.1405) .

Practical guidance

• ADUs are subject to objective design checks and a 60‑day ministerial review per § 10-1.1406; confirm ADU setbacks vs. existing primary dwelling siting early in the design (§ 10-1.1406) .

SB 9 / Two‑Unit Split Rules (Article 15 / § 10‑1.1500+)

Where applicable

• SB 9 lot splits and SB 9 units are allowed in eligible R‑A parcels per Article 15 subject to Town and State eligibility rules (§ 10-1.1503 et seq.) .

Key objective standards (decision‑relevant)

• SB 9 unit size: single SB 9 unit maximum 900 sq ft; SB 9 unit maximum height 16 ft; MDA for SB 9 lot equals MFA + 2,100 sq ft cap for additional development area on SB 9 lots (§ 10-1.1505) .
• SB 9 parking: one on‑site parking space required per SB 9 unit unless within one‑half mile of major transit/high‑quality transit corridor or other exemptions (§ 10-1.1505(e)) .
• SB 9 safety and design: SB 9 units must have fire sprinklers, one‑hour fire wall separation, utility undergrounding, no roof decks, and required landscape screening; see § 10-1.1506 for the full list (§ 10-1.1506) .

Practical guidance

• SB 9 projects must meet both State SB 9 eligibility and these local objective standards; review the Town's SB 9 article for parcel‑specific prohibitions (e.g., historic district exclusion) (§ 10-1.1503) .

Quick Standards Table (decision‑relevant at a glance)

Checklist — what an applicant must satisfy (pre‑application)

• Confirm parcel eligibility and net area (§ 10-1.501) .
• Calculate Lot Unit Factor (LUF) and average slope (S) and compute MDA and MFA per § 10-1.502 and § 10-1.503 .
• Verify setbacks: front, side, rear per § 10-1.505 and any special estate home setback formulas (§ 10-1.508) .
• Check height limits: base 27 ft, exceptions/step‑ups and the 35 ft special cap (§ 10-1.504) .
• Meet parking rules for the proposed use (primary dwellings, ADUs, SB 9 units) (§ 10-1.601, § 10-1.1403, § 10-1.1505) .
• Include landscape screening plans where required (estate homes, some large projects) (§ 10-1.508) .
• If proposing an ADU, follow Article 14 objective standards and confirm compliance with the California Building Standards Code where applicable (§ 10-1.1403, § 10-1.1405) .
• Determine whether the project is ministerial (e.g., many ADUs) or requires Site Development or Planning Commission review (thresholds in § 10-2.301) .
• Check for overlays or historic status that may restrict SB 9 or other approvals (see Los Altos Hills Overlay Districts and § 10-1.1503) .

Risks & Ambiguities

Plain‑English summary

Los Altos Hills uses slope and Lot Unit Factor (LUF)‑based formulas to set how big a house and how much lot coverage you can build; typical targets are an acre‑minimum lot, a 27 ft height standard (with conditional step‑ups to 32 ft and an absolute 35 ft cap), front setbacks commonly measured at 40 ft, and strong limits on development area and floor area tied to your lot's slope and LUF (§ 10-1.501–10-1.505, § 10-1.502, § 10-1.503, § 10-1.504) .

Source References

• Town of Los Altos Hills, Zoning & Site Development (Title 10), Article 5 (Area/Coverage/Height/Setbacks) — § 10-1.501, § 10-1.502, § 10-1.503, § 10-1.504, § 10-1.505 .
• Article 6 Off‑Street Parking — § 10-1.601 (parking counts and dimensions) .
• Article 7 Residential‑Agricultural (R‑A) — § 10-1.701 – 10-1.706 (permitted uses, R‑A applicability) .
• Article 8 Open Space Reserve (OSR) — § 10-1.801 – 10-1.804 (uses and reference to Article 5) .
• Estate Homes — § 10-1.508 (additional setbacks and height rules) .
• Variances / Conditional Development Permits — § 10-1.1007 (who hears MDA/MFA/setback/height exceptions) .
• ADUs (Article 14) — § 10-1.1401 – 10-1.1407 (ADU size, setbacks, height, incentives, ministerial review) .
• SB 9 Article (Article 15) — § 10-1.1503, § 10-1.1505, § 10-1.1506 (lot split eligibility, SB 9 unit size/height/parking, special conditions) .
• Permit thresholds and administrative review rules — § 10-2.301 (what triggers Planning Commission vs. Director) .
• Town code references used above are from the Los Altos Hills Zoning Code extract supplied (Title 10, Zoning & Site Development) — source file LosAltosHills_ZoningCode.md (ecode360 snapshot) .

Retrieved passages

• Los Altos Hills Zoning Code (§ 10-1.1007) High relevance show source text
• Los Altos Hills Zoning Code (§ 10-1.1504) High relevance show source text
• CBC § 2 (§ 2) High relevance show source text
• Los Altos Hills Zoning Code (section for) High relevance show source text
• Los Altos Hills Zoning Code (Section 10-1.202.) High relevance show source text
• Los Altos Hills Zoning Code (§ 10-1.504) High relevance show source text
• Los Altos Hills Zoning Code (Section 10-1.505) High relevance show source text
• Los Altos Hills Zoning Code (section nor) High relevance show source text
• Los Altos Hills Zoning Code (§ 10-1.704.) High relevance show source text
• Los Altos Hills Zoning Code (§ 1) High relevance show source text
• Los Altos Hills Zoning Code (Section 10-2.1305) High relevance show source text
• Los Altos Hills Zoning Code (§ 10-1.503.) High relevance show source text
• Los Altos Hills Zoning Code (§ 10-1.703) High relevance show source text
• Los Altos Hills Zoning Code (Article 7) High relevance show source text
• Los Altos Hills Zoning Code (section for) High relevance show source text
• Los Altos Hills Zoning Code (Section 10-1.505) High relevance show source text
• Los Altos Hills Zoning Code (§ 1) High relevance show source text
• Los Altos Hills Zoning Code (§ 10-1.507) High relevance show source text

Cited sections

• Town of Los Altos Hills, Zoning & Site Development (Title 10), Article 5 (Area/Coverage/Height/Setbacks) — § **10-1.501**, § **10-1.502**, § **10-1.503**, § **10-1.504**, § **10-1.505** . (Title 10)
• Article 6 Off‑Street Parking — § **10-1.601** (parking counts and dimensions) . (Article 6)
• Article 7 Residential‑Agricultural (R‑A) — § **10-1.701** – **10-1.706** (permitted uses, R‑A applicability) . (Article 7)
• Article 8 Open Space Reserve (OSR) — § **10-1.801** – **10-1.804** (uses and reference to Article 5) . (Article 8)
• Estate Homes — § **10-1.508** (additional setbacks and height rules) .
• Variances / Conditional Development Permits — § **10-1.1007** (who hears MDA/MFA/setback/height exceptions) .
• ADUs (Article 14) — § **10-1.1401** – **10-1.1407** (ADU size, setbacks, height, incentives, ministerial review) . (Article 14)
• SB 9 Article (Article 15) — § **10-1.1503**, § **10-1.1505**, § **10-1.1506** (lot split eligibility, SB 9 unit size/height/parking, special conditions) . (Article 15)
• Permit thresholds and administrative review rules — § **10-2.301** (what triggers Planning Commission vs. Director) .
• Town code references used above are from the Los Altos Hills Zoning Code extract supplied (Title 10, Zoning & Site Development) — source file LosAltosHills_ZoningCode.md (ecode360 snapshot) . (Title 10)
• LosAltosHills_ZoningCode.md

• Official Los Altos Hills code library