Local zoning · Hillsborough

Hillsborough — Development Standards

Q: What are Hillsborough front and interior setback requirements?

The code defines a 25‑foot street‑line setback area and a 20‑foot interior setback area as the default objective setbacks; measure per the diagrams and measurement rules in the code § 17.24.020–030 .

Q: How does Hillsborough measure height and building bulk?

Hillsborough uses a building envelope: structures start at existing grade , rise 22 ft above the setback line, then slope inward at 45° to a maximum 32 ft measured from a warped plane; check the "existing grade" definition as it affects your envelope § 17.28.010 .

Q: What is the FAR limit for a single‑family property?

Total covered floor area may not exceed 25% of net lot area for the first acre plus 15% over one acre ; the code describes how to count basements, attics, and tall spaces — consult § 17.32.020 and § 17.32.030 .

Q: How much of my lot can be covered by structures and hardscape?

Combined structural plus hardscape coverage is capped at 50% of the net lot area; within the street‑line setback area the cap is 40% . Structural coverage tables by lot size determine the structural maximum in square feet § 17.32.060 .

Q: When will I need design review or City Council review?

Large primary dwellings above 8,000 sq ft trigger City Council review after Architecture & Design Review Board consideration; ADU exceptions and alterations to nonconforming structures may require design review under Chapter 2.12 and the ADU chapter § 17.32.040 and § 17.52.020 .

Development Standards under the Hillsborough local zoning and planning code, with the controlling citations.

Ask a question free See coverage

Last reviewed: July 2, 2026

Overview

This page summarizes the Hillsborough municipal zoning rules that control setbacks, height, lot coverage, floor area ratio (FAR) and density for the town's zoning districts. It is grounded in Title 17 of the Hillsborough Municipal Code (the Hillsborough Zoning Ordinance) and explains how the rules interact with accessory dwelling units (ADUs), two‑unit projects, and design review. For quick reference to the town's zoning framework, see the Hillsborough Zoning page. Also note local rules reference ministerial requirements for parking, design review, and state building rules such as the California Building Standards Code.

District-by-district development standards (what the ordinance actually says)

The Town restructured its districts in its 2024 ordinance. The primary districts are RD-1, RD-2, and RD-3; their basic purposes and density rules are in § 17.12.010 and the allowed uses are summarized in § 17.16.010 .

RD-1 — Traditional residential (RD-1)

Purpose and typical uses: intended for single‑family dwellings to "retain the scale and character of existing residential neighborhoods"; typical permitted use is a single-family dwelling; accessory uses (garages, ADUs subject to ADU chapter) are allowed under other chapters § 17.04.010 and § 17.16.010 .
Density: maximum allowed density is one single‑family dwelling per one‑half acre (exclusive of ADUs) § 17.16.010 .
Key dimensional controls that apply (applied town‑wide unless otherwise stated):
- Front (street‑line) setback: default street‑line setback area is a 25‑foot strip measured from the street line; see § 17.24.020 .
- Interior setback: 20‑foot interior setback area measured from non‑street lot lines § 17.24.020 .
- Building envelope / height: building envelope rises 22 ft above existing grade at setback line then slopes inward at 45° to a maximum 32 ft measured from a warped plane (this is the primary height/volume limit) § 17.28.010 .
- FAR (single‑family): total covered floor area limits equal 25% of net lot area for the first acre + 15% of net lot area over one acre (the code expresses allowed total covered floor area as that percentage—i.e., the FAR formula) § 17.32.030 .
- Lot coverage: structural coverage formulas and caps (table) and combined structural + hardscape caps apply (combined structural + hardscape ≤ 50% of net lot — and 40% limit within street‑line setback area); see § 17.32.060 and the coverage table .
Where it applies: wherever the zoning map designates RD‑1; see the Zoning Map requirement § 17.04.030 .

RD-2 — Mixed residential (RD-2)

Purpose and typical uses: established to allow townhouses and multifamily on specific parcels and town‑owned land; minimum density 20 units per acre (intended where multi‑unit development is appropriate) § 17.16.010 .
Dimensional standards: the same town‑wide development standard chapters apply (setbacks § 17.24.020; height envelope § 17.28.010; FAR/lot coverage chapters § 17.32.020–060), but multifamily parcels sometimes are subject to site‑specific standards and ADU/JADU rules differ when multifamily conversions occur § 17.52.020 .
Special ADU allowances: converted ADUs within existing multifamily dwellings and limited detached ADUs on multifamily properties have tailored limits (see § 17.52.020(C) for quantity and setback rules) .

RD-3 — Governmental and residential mixed use (RD-3)

Purpose and typical uses: accommodates town facilities and limited residential units on town‑owned land; up to 16 dwelling units allowed on land zoned RD‑3 § 17.16.010 .
Dimensional standards: RD‑3 uses the same Chapters for setbacks, height, FAR and coverage unless the code or project approval establishes alternative standards; private schools and public facilities have additional setback rules (e.g., private schools: 25 ft from a street line, 20 ft from other property lines) § 17.16.030 .

Town‑wide numeric standards and rules (at-a-glance)

The following table highlights the standards most likely to determine whether a proposed project will be allowed or require exceptions. Code references are given for each line.

Standard / item	What Hillsborough's code requires (practical)	Code reference
Zoning districts established	RD‑1, RD‑2, RD‑3 (map on file with City Clerk) — uses listed in § 17.16.010	§ 17.12.010; § 17.16.010
Front (street‑line) setback area	25 ft street‑line setback (measured per diagram rules)	§ 17.24.020
Interior setback area	20 ft interior setback strip	§ 17.24.020
Building envelope / height	Envelope: 22 ft above grade at setback then 45° inward to 32 ft max (warped plane)	§ 17.28.010
FAR / max total covered floor area	25% of net lot area for first acre + 15% of net lot area over 1 acre (FAR expressed as percent of lot)	§ 17.32.030
Structural + hardscape cap	Combined structural + hardscape ≤ 50% of net lot; within street‑line setback area combined ≤ 40%	§ 17.32.060
Special increase for very large homes	Homes > 8,000 sq ft: aggregate setbacks increased by 15 ft (minimum +5 ft to street line)	§ 17.24.020(F)
ADU minimum setbacks	ADU side & rear: 4 ft (minimum); ADU front setback: 25 ft (with exceptions)	§ 17.52.020(E)
ADU height limits (detached)	Detached ADU generally 16 ft; up to 18 ft (transit prox./multifamily) and other limited conditions up to 22 ft with spacing § 17.52.020(E)	§ 17.52.020(E)
Two‑unit projects (urban lot split)	Special unit, size, height and setback rules apply (see Chapter 17.54)	§ 17.54.050 et seq.

Notes: Many items above are measured from existing grade as defined in the code; the precise measurement point and treatment of basements, attic areas, and high‑ceiling spaces are described in § 17.32.020 (total covered floor area rules) .

How these rules interact in practice — plain English synthesis and practical guidance

FAR in Hillsborough is expressed as a percent of net lot area (the code gives 25% + 15% over one acre) and is applied to the legally defined "total covered floor area" calculated to exterior walls; basements, high ceilings, and other special spaces have specific counting rules — see § 17.32.020 and § 17.32.030 .
Height is not a single number for every lot: the town uses a building envelope (22 ft then 45° slope to 32 ft) to control bulk and massing rather than only a numeric cap; measure existing grade carefully — the code's "existing grade" rules determine where that envelope begins § 17.28.010 .
Lot coverage is split conceptually between "structural" and "hardscape" coverage; these combine against a 50% cap for the lot overall and a 40% cap inside street setbacks — the numeric table and calculation rules are in § 17.32.060 .
ADUs have their own chapter with ministerial standards that cannot be used to prohibit at least an 800 sq ft ADU with 4 ft side/rear setbacks in most cases — consult the ADU chapter and state ADU law: § 17.52.020 (ADUs) and state law overview (local ADU rules are implemented in the code) . For Hillsborough ADU process and requirements see the ADU chapter and the ADU page.
Design review (the Architecture & Design Review Board) is tied into nonconforming repairs, large homes (>8,000 sq ft require council review after design board action) and some ADU exceptions; expect design review for discretionary exceptions § 17.32.040 and Chapter 2.12 references in the ADU chapter .

Inline resources you may want now: the town's pages on parking, design review, overlay districts, and ADUs. When the code references the building standards it defers to the California Building Standards Code.

Checklist (what an applicant must satisfy before you can expect a ministerial or typical discretionary approval)

Verify the lot's zoning district (RD‑1/RD‑2/RD‑3) on the official zoning map § 17.04.030 .
Calculate net lot area and allowable FAR (25% first acre + 15% over 1 acre) against "total covered floor area" counting rules § 17.32.020–030 .
Measure and confirm front (25 ft) and interior (20 ft) setback areas, and confirm any special >8,000 sq ft setback increases § 17.24.020–030 .
Draw the building envelope: 22 ft at setback rising at 45° to 32 ft warped‑plane max; verify existing grade baseline § 17.28.010 .
Compute structural coverage / hardscape and ensure combined cap ≤ 50% (and ≤40% within street setbacks) § 17.32.060 .
For ADUs: confirm ADU type (conversion vs detached) and that ADU dimensions, setbacks, heights and parking conform to § 17.52.020; if seeking exceptions, prepare for design review § 17.52.020 .
Identify whether the project requires Architecture & Design Review or City Council review (e.g., >8,000 sq ft primary dwelling triggers council submission after ARDB review) § 17.32.040 .
Confirm parking requirements and any exemptions (see Hillsborough parking standards) Chapter 17.36 .
If nonconforming conditions exist, document them and check alteration/rebuilding rules § 17.20.020 .

Risks & Ambiguities

Issue	Why it matters	What to verify
Existing grade baseline for building envelope	"Existing grade" definition (natural vs. altered five‑year rule) can change allowable envelope and max height	Confirm how building department will determine "existing grade" for the parcel and get that determination in writing § 17.28.010
Which coverage table applies	Structural coverage uses a graduated table tied to net lot area; mis‑application changes allowable footprint	Calculate using the town's structural coverage table and confirm which table row applies to your net lot area § 17.32.060
ADU exceptions vs ministerial ADU rules	State ADU law constrains local rules; some ADU sizes, heights, and setbacks are protected — but local ADU exceptions can require design review	Determine whether your ADU is ministerial under § 17.52.020(C) or requires an ADU planning permit and whether a design‑review exception is needed
Nonconforming structures & remodeling	Nonconforming height, FAR, or setbacks can allow remodeling under limits but could block larger reconstructions	If structure is nonconforming, validate what is allowed under § 17.20.020 and obtain pre‑application advice from planning
Parcel-specific mapping (RD‑2/3 special parcels)	RD‑2 and RD‑3 are intended for specific town parcels; assuming a district's density/uses without map verification risks improper application	Confirm the parcel on the zoning map per § 17.04.030 and consult the planning office § 17.12.010

Plain-English Summary

Hillsborough controls building size and placement primarily through a measured building envelope (22 ft then a 45° slope to 32 ft), percent‑based floor area limits (FAR = 25% of the first acre + 15% over an acre), and a combined structural + hardscape coverage cap of 50%; front and interior setbacks are generically 25 ft and 20 ft, respectively, with ADUs and two‑unit projects subject to their own adjusted rules — verify your parcel's district and exact measurements with the Planning Department before design work. Key citations: § 17.24.020, § 17.28.010, § 17.32.030, § 17.32.060, § 17.52.020 .

Source References

Hillsborough Municipal Code, Title 17 — Zoning: Chapters and context (Title summary and purposes) § 17.04.010—17.04.030
Zoning districts established: § 17.12.010 (RD‑1, RD‑2, RD‑3)
Permitted uses and district summaries: § 17.16.010 (RD‑1/RD‑2/RD‑3 uses and densities)
Setbacks and location rules (street‑line = 25 ft; interior = 20 ft; diagrams & special 8,000 sq ft rule): § 17.24.020; measurement rules § 17.24.030
Height/building envelope: § 17.28.010 (22 ft then 45° to 32 ft)
Residential size, FAR, and counting rules: § 17.32.020; FAR maximums § 17.32.030; large‑home review § 17.32.040
Lot coverage types and table (structural/hardscape caps, combined 50% cap, setback‑area 40% cap): § 17.32.060 (table included)
ADU/JADU conversion and ministerial ADU standards (setbacks, heights, parking, exceptions): Chapter 17.52 / § 17.52.020
Two‑unit projects & urban lot split standards: Chapter 17.54 / § 17.54.050 et seq.
Nonconforming structures & alterations: Chapter 17.20 / § 17.20.020
Hillsborough parking rules and minimum spaces: Chapter 17.36 (referenced in ADU & two‑unit chapters)

(Where a single topic is handled across multiple code sections the primary controlling § is listed above. For ADU state law context, see California ADU guidance materials cited in local ADU chapter updates — summary notes in town files.)

Sources

Retrieved passages

Hillsborough Zoning Code (Section 17.32.030) High relevance
Hillsborough Zoning Code (chapter is) High relevance
Hillsborough Zoning Code (chapter of) High relevance
Hillsborough Zoning Code (Section 21155) High relevance
Hillsborough Zoning Code High relevance
Hillsborough Zoning Code (chapter must) High relevance
Hillsborough Zoning Code (Section 21155) High relevance
California Fire Code High relevance
CBC § 66314 (§ 66314) Medium relevance
CFC § 310 (Section 310) Medium relevance
Hillsborough Zoning Code (Section 17.24.030) Medium relevance
Hillsborough Zoning Code (section 66333) Medium relevance
Hillsborough Zoning Code (§ 66317) Medium relevance
Hillsborough Zoning Code (section are) High relevance
Hillsborough Zoning Code (Chapter 2.12) Medium relevance
Hillsborough Zoning Code (§ 16) Medium relevance
Hillsborough Zoning Code (section are) Medium relevance

Cited sections

Official Hillsborough code library

Frequently asked questions

What can I build on an RD‑1 lot in Hillsborough?

RD‑1 (Traditional Residential) is intended for single‑family dwellings with accessory structures and ADUs allowed under the ADU chapter; maximum base density is one single‑family dwelling per one‑half acre (ADUs are treated separately under Chapter 17.52). See § 17.12.010 and § 17.16.010 for district establishment and uses and § 17.52.020 for ADU rules .

What are Hillsborough front and interior setback requirements?

The code defines a 25‑foot street‑line setback area and a 20‑foot interior setback area as the default objective setbacks; measure per the diagrams and measurement rules in the code § 17.24.020–030 .

How does Hillsborough measure height and building bulk?

Hillsborough uses a building envelope: structures start at existing grade, rise 22 ft above the setback line, then slope inward at 45° to a maximum 32 ft measured from a warped plane; check the "existing grade" definition as it affects your envelope § 17.28.010 .

What is the FAR limit for a single‑family property?

Total covered floor area may not exceed 25% of net lot area for the first acre plus 15% over one acre; the code describes how to count basements, attics, and tall spaces — consult § 17.32.020 and § 17.32.030 .

How much of my lot can be covered by structures and hardscape?

Combined structural plus hardscape coverage is capped at 50% of the net lot area; within the street‑line setback area the cap is 40%. Structural coverage tables by lot size determine the structural maximum in square feet § 17.32.060 .

Do ADUs have different setbacks and heights in Hillsborough?

Yes. ADUs are governed by Chapter 17.52: minimum side/rear setbacks for many ADUs are 4 ft, front setback 25 ft (with specific exceptions), and detached ADUs generally limited to 16 ft height with conditional allowances to 18–22 ft in limited circumstances; parking rules for ADUs are also established in that chapter § 17.52.020 .

When will I need design review or City Council review?

Large primary dwellings above 8,000 sq ft trigger City Council review after Architecture & Design Review Board consideration; ADU exceptions and alterations to nonconforming structures may require design review under Chapter 2.12 and the ADU chapter § 17.32.040 and § 17.52.020 .

If my home is legally nonconforming, can I remodel or enlarge it?

Yes, subject to limits: a nonconforming structure that encroaches into setbacks may be altered if the encroachment is not increased, new work within the setback does not exceed 22 ft in height, and certain findings are made (fire/safety and design board findings) — see § 17.20.020 .

What does Hillsborough require for parking on a new dwelling?

Hillsborough sets parking standards in Chapter 17.36; for typical dwellings a garage is required for new or substantially enlarged dwellings and dimensional minimums for spaces and backup area are specified. ADU parking is addressed in the ADU chapter with specified exemptions Chapter 17.36 and § 17.52.020 .

How do two‑unit projects differ from ADUs?

Two‑unit projects (Chapter 17.54) implement state two‑unit/urban lot split rules and set unit size, height, setback and owner‑occupancy requirements distinct from ADU rules; two‑unit projects have their own ministerial rules and checks (e.g., owner occupancy, fire mitigation for high fire zones) § 17.54.050 et seq.

Ask about any Hillsborough property

Get a cited, plain-English answer on Hillsborough zoning, setbacks, FAR, ADUs and permits — for any address.

Start Free Trial