Local zoning · Tuolumne County

Tuolumne County — Overlay Districts

Q: How does the Historic Design Preservation (HDP) district affect parking and design review?

For HDP , underlying uses remain, but exterior changes typically require a use permit and Historic Preservation review; commercial parcels are given a special parking ratio of one space per 250 sq ft , with off‑site parking or in‑lieu fees allowed under certain conditions. See § 17.20.030(C) .

Q: If my parcel is in an Airport Combining (:AIR) district, what limits should I expect?

Expect to follow the ALUCP compatibility-zone rules: density and use restrictions , strict height limitations in critical zones (referencing FAR Part 77 and Chapters 18.24/18.28), and possible prohibition of uses that attract birds, create glare, or interfere with flight. Check the ALUCP maps and § 17.20.050 .

Q: Do combining districts change base zoning uses (e.g., allow new commercial uses)?

Generally, combining districts do not change the underlying allowed uses—the base zoning still controls uses unless the combining district expressly prohibits or conditions specific uses (common in the Airport Combining District). Always read the specific combining-district § and the underlying zone’s use table. See § 17.20.010–050 .

Q: Are mobile homes allowed anywhere with the :MX overlay?

Within a Mobile Home Foundation Combining ( :MX ) District, mobile/manufactured homes may be used on individual parcels only if installed on an approved foundation and meeting skirting and age requirements set out in § 17.20.040 ; mobile home parks are regulated separately. See § 17.20.040 .

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

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Last reviewed: July 3, 2026

Overview

Overlay (combining) districts in Tuolumne County are special “layers” applied on top of the county's base zoning that modify or supplement the underlying zoning rules for particular lands (historic areas, airport influence areas, mobile‑home foundation requirements, agricultural preserves, planned developments, etc.). The combining districts are codified in Title 17 (Article 3, Chapter 17.20) and set purposes, criteria, permit requirements, and the specific ways they change development standards for the unincorporated areas of Tuolumne County. See the Tuolumne County zoning & planning overview for the broader context. § 17.20.010–17.20.050

How Tuolumne County implements overlays (quick summary of rules)

Overlays are called Combining Districts in Title 17; they do not replace the base zone but supplement or modify it. Uses allowed generally remain the underlying zone's uses unless a combining district explicitly alters that (e.g., Airport Combining restrictions). § 17.20.010, § 17.20.020
Many combining districts require a use permit or other discretionary approvals prior to changing setbacks, heights, landscaping, or parking rules; others allow limited exceptions without permits. See each district below for specifics. § 17.20.030–17.20.050
Where the combining district modifies development standards, it will say which standards can be altered (setbacks, heights, parking, landscaping) and whether a use permit or Director action is required. § 17.20.020(C)–(D)

District-by-district breakdown

The most used combining (overlay) districts in the Tuolumne County Title 17 combining-district chapter include the following. For each I summarize purpose, typical permitted uses (how the overlay treats underlying uses), key dimensional or process effects, and where it typically applies.

Note: All rules below apply only to Tuolumne County unincorporated areas. Verify parcel‑specific applicability with the County maps/Planning Department.

Historic Combining District — H (§ 17.20.020)

Purpose: Preserve and enhance places and things of local/state/national historic importance. § 17.20.020
Typical permitted uses: Uses allowed are those of the underlying zone; the H designation does not change the underlying use table unless specifically stated. § 17.20.020(B)
Key modifications / rules:
- Modifications to setbacks, height, landscaping, and parking are generally suspended until a use permit is obtained — i.e., many standards do not apply unless the property owner secures a use permit; however, certain narrow exceptions are allowed without a permit (for example parking rules for commercial uses). § 17.20.020(C)–(D)
- The State Historical Building Code may be used for buildings in the H district. § 17.20.020(C)(1)
Where it applies: Parcels rezoned to H by Board ordinance after findings; owner consent is required for an H rezoning. § 17.20.020(A)(4)
Practical note: If your parcel is in H, expect referral to the Historic Preservation Review Commission and extra procedural steps before exterior changes — see Tuolumne County Historic Preservation and the County’s design-review process. § 17.20.020(E)–(I)

(First mention links: historic preservation and design review are referenced inline; see the linked pages for related processes.)

Historic Design Preservation Combining District — HDP (§ 17.20.030)

Purpose: Preserve and enhance historic character across an area containing multiple cultural resources; created where a majority of property owners consent and the Historic Preservation Review Commission supports it. § 17.20.030(A)–(B)
Typical permitted uses: Underlying zone uses remain; the HDP primarily changes review and design requirements. § 17.20.030(B)
Key modifications / rules:
- Many development standards (setbacks, heights, landscaping, parking) may be suspended or modified but only after the required use permit and review; some limited actions (ordinary maintenance, same‑size window/door replacement, small compatible signage) are allowed without a use permit but must be compatible with the historic district design guidelines. § 17.20.030(C)–(E)
- For commercial parcels within an HDP, the code sets a special parking standard: one parking space per 250 sq ft for commercial (treated as shopping-center type), with off‑site parking/in‑lieu fees allowed in certain cases. § 17.20.030(C)(1)–(2)
Where it applies: Boundaries are set by ordinance after public hearing; property-owner consent and commission review required. § 17.20.030(A)(2)–(4)

(First mention links: parking and design review were linked earlier.)

Mobile Home Foundation Combining District — :MX (§ 17.20.040)

Purpose: Ensure older mobile homes used as residences on individual parcels are placed on foundations where required to protect neighborhood character and safety. § 17.20.040(A)
Typical permitted uses: Mobile/manufactured homes may be allowed on individual lots except where an MX exclusion or the underlying zone forbids residences; mobile home parks are treated separately. § 17.20.040(B)–(C)
Key standards:
- Foundation requirement per the current California Building Code (Title 24) and Health & Safety Code § 18551; mobile home age limits and skirting requirements apply for guesthouses. § 17.20.040(A)–(B)
Where it applies: Applied as a combining district to parcels where the County has determined foundation requirements are necessary. § 17.20.040

(First mention link: California Building Standards Code / Title 24 linked inline when referencing foundation standards.)

Airport Combining District — :AIR (§ 17.20.050)

Purpose: Protect public safety and minimize noise/safety hazards in airport influence areas; ensure consistency with the Tuolumne County airport land use compatibility plan (ALUCP). § 17.20.050(A)–(B)
Typical permitted uses: Underlying uses remain but subject to compatibility constraints; the overlay may prohibit or restrict specific uses listed in the code and ALUCP. § 17.20.050(D)
Key standards / effects:
- Development must comply with the airport land use compatibility plan; density and intensity limits are tied to ALUCP compatibility zones and mapped Exhibits A/B. § 17.20.050(B)–(C)
- Height restrictions are strict in critical zones and reference Federal Aviation Regulations Part 77 and Chapters 18.24/18.28; certain zones may effectively limit heights to very low levels or ground level. § 17.20.050(G)
- Where parcels cross compatibility zone boundaries, the code treats them as if divided at the boundary for density calculations; the code also allows density transfers to less‑restricted parts of a parcel or project in specified ways. § 17.20.050(D)(1)–(2), (M)
Where it applies: To property falling within ALUCP airport influence area boundaries for Columbia and Pine Mountain Lake Airports (Exhibits A & B referenced). § 17.20.050(A),(C)

(First mention link: link to Tuolumne County Land Use is provided when discussing airport land use compatibility; for parcel‑level boundaries verify maps with the County.)

Planned Unit Development Combining District — :PD (§ 17.20.010 description)

Purpose: Provide flexibility and integrated design for large or mixed projects (diverse uses, open spaces, clustering) while ensuring General Plan consistency. § 17.20.010 (Purposes of combining districts; PD described)
Typical permitted uses: The PD is applied in combination with base zoning and replaces strict parcel-by-parcel standards with an approved PD plan that sets site‑specific development standards and allowed uses.
Key standards:
- A PD typically requires a comprehensive discretionary approval process where the Planning Commission and/or Board approve a master plan; development standards (setbacks, lot sizes, open space, parking) are set in the PD approval. § 17.20.010
Where it applies: Specific projects and mapped areas as established by ordinance/PD approval. Verify with County for active PD boundaries.

Agricultural Preserve Combining District — :AP (§ 17.20.010)

Purpose: Implement Williamson Act / agricultural preserve policies, preserve agricultural/open-space values, and limit incompatible uses. § 17.20.010 (AP description)
Typical permitted uses: Agricultural operations are favored; other uses are restricted or conditioned consistent with Williamson Act contracts and County policy. § 17.20.010

Decision-critical table (overlay summary)

Combining (Overlay) District	Purpose (plain)	Key immediate effect on development	Code reference
H (Historic Combining District)	Preserve individual historic properties	Underlying uses remain; many development standards suspended until a use permit; limited exceptions (e.g., certain parking rules)	§ 17.20.020
HDP (Historic Design Preservation)	Preserve historic character of an area	Requires use permit/design review for exterior changes; special parking rules (commercial: 1 space / 250 sq ft) and possible landscaping reductions	§ 17.20.030
:MX (Mobile Home Foundation)	Require foundations/skirting for mobile homes	Mobile/manufactured homes must meet foundation and age/skirting rules; mobile home parks treated separately	§ 17.20.040
:AIR (Airport Combining)	Protect airports and adjacent public safety	Must follow ALUCP; density, use prohibitions, strict height limits in critical zones; compatibility maps control applicability	§ 17.20.050
:PD (Planned Unit Development)	Allow integrated, flexible site plans	Replaces prescriptive standards with PD-approved standards (setbacks, open space, design)	§ 17.20.010
:AP (Agricultural Preserve)	Enforce Williamson Act preserves	Limits non‑agricultural development consistent with preserve/contract	§ 17.20.010

Practical guidance and how overlays change the project review

Always start by confirming whether a parcel is mapped for any combining district: overlays are map overlays applied to parcels — if present, the combining-district rules are binding and often add discretionary steps (use permits, referrals to commissions). Verify with the County Planning Department (parcel map / GIS). Not found in retrieved materials: the actual map layers/Exhibits A & B referenced for the Airport Combining District. § 17.20.050(C)
If a property is in H or HDP, expect referral to the Historic Preservation Review Commission and possible design standards or a requirement to apply the State Historical Building Code; check the County's design‑review steps and Historic Preservation pages. § 17.20.020(E), § 17.20.030(D)
If in the :AIR district, check the ALUCP compatibility zone (A, B1, B2, C, D) — density, allowed uses and height limits depend on the compatibility zone; some parcels that straddle zones are treated as separate areas for density calculations and may be eligible for density transfer. § 17.20.050(D)–(G)
For properties in :MX, ensure any mobile/manufactured home installations comply with foundation requirements in the current Title 24 and Health & Safety Code references; these rules are specifically called out in the combining district. § 17.20.040(A)
Many combining districts allow the Director discretion to reduce standards such as landscaping area or require off‑site or in‑lieu parking; applicants should be prepared to justify alternatives and provide mitigation. § 17.20.020(C)(1)(c), § 17.20.030(C)(2)

(First mention links: development standards, landscaping and screening, variances and exceptions, parking, design review, and zoning pages are linked inline in the relevant sentences above.)

Checklist (what an applicant must satisfy when an overlay applies to their parcel)

Confirm overlay(s) on the parcel via County GIS / Planning (verify whether H, HDP, :AIR, :MX, :PD, :AP apply). Verify with the jurisdiction. Not found in retrieved materials: parcel-specific map extracts. § 17.20.050(C)
Review the underlying zoning district’s allowable uses and development standards in Title 17. § 17.02.050; Article 2 chapters for base zone rules.
Determine whether the combining district requires a use permit or other discretionary approval (H/HDP commonly do). § 17.20.020–030
For H/HDP, obtain or prepare to obtain recommendations from the Historic Preservation Review Commission and conform to adopted design guidelines where required. § 17.20.020(E)–(I), § 17.20.030(E)
For :AIR, secure any ALUCP consistency determinations and check height/density limits for the parcel’s compatibility zone; prepare for possible density transfer requirements or restrictions. § 17.20.050(B),(D),(G)
For :MX, ensure mobile home foundation and skirting details comply with the California Building Standards Code/Health & Safety Code conditions. § 17.20.040(A)
Where the overlay permits alternative compliance (e.g., off‑site parking, in‑lieu fees, landscape credits), prepare documentation and proposed agreements for Director review. § 17.20.020(C)(1)(b)–(c), § 17.20.030(C)(2)
Confirm whether any referred chapters (e.g., Chapters 18.24 / 18.28 for airport rules) apply; gather any federal/state code references cited by the combining district. § 17.20.050(B),(G)

Risks & Ambiguities

Issue	Why it matters	What to verify
Overlay boundary mapping (Airports / Historic districts)	Overlay rules only apply where mapped. Misreading the map can lead to unnecessary denials or missed requirements.	Verify parcel’s overlay status with County GIS/Planning and request Exhibits A/B (Airport) if needed. § 17.20.050(C)
Treatment of development standards in H/HDP	The code allows suspension/modification of setbacks, parking, landscaping — but often only after a use permit. A misunderstanding can produce design noncompliance.	Confirm which standards are exempted vs. which are allowed without a permit (see § 17.20.020(C)–(D) and § 17.20.030(C)).
Density transfers in Airport Combining (:AIR)	Transfer rules allow shifting development potential, but require permanent release or conditions — complicated for multi‑parcel projects.	Verify transfer procedures and any required legal instruments or conditions with the County and ALUC. § 17.20.050(D)–(E)
Current list of parcels zoned H or HDP	The ordinance describes the criteria and process but not the current inventory of historic parcels.	Ask Planning for the current list of H/HDP parcels and applicable design guides. § 17.20.030(A),(4)
How overlays affect ministerial ADU approvals	Overlays may add discretionary steps that conflict with statewide ADU rules if misapplied.	Not found in retrieved materials: No explicit crosswalk for ADUs in combining districts. Verify with County and review California ADU law. § 17.20.010–050 (no ADU-specific cross reference found)
Use of State Historical Building Code within H/HDP	The code allows it, but application specifics (when it overrides local standards) require clarity.	Review § 17.20.020(C)(1) and consult Building/Planning departments on application of the State Historical Building Code.

Plain-English summary

If your property in unincorporated Tuolumne County has an overlay/combining district on it — for example H, HDP, :AIR, or :MX — the overlay adds extra rules or review steps on top of the usual zoning. Often the underlying uses stay the same, but expect additional permit reviews (use permits, design review, referrals to historic or airport bodies), special parking/landscaping rules, and strict height/density limits near airports. Always check the County’s maps and the specific combining-district § that applies to your parcel before designing a project. See §§ 17.20.010–17.20.050.

Source References

Tuolumne County Uniform Zoning Ordinance (Title 17) — Combining Districts: § 17.20.010 (Purpose)
Tuolumne County Uniform Zoning Ordinance — Historic Combining District § 17.20.020
Tuolumne County Uniform Zoning Ordinance — Historic Design Preservation (HDP) § 17.20.030
Tuolumne County Uniform Zoning Ordinance — Mobile Home Foundation (:MX) § 17.20.040
Tuolumne County Uniform Zoning Ordinance — Airport Combining (:AIR) § 17.20.050
Tuolumne County zoning & planning overview (/us/california/tuolumne-county) — context and county web resources
Tuolumne County Zoning (/us/california/tuolumne-county/zoning) — base zoning chapters and maps
Tuolumne County Land Use (/us/california/tuolumne-county/land-use) — ALUCP and related land-use materials
Tuolumne County Development Standards (/us/california/tuolumne-county/development-standards) — for standards referenced by combining districts
Tuolumne County Parking (/us/california/tuolumne-county/parking) — parking standards and in‑lieu options referenced in H/HDP
Tuolumne County Historic Preservation (/us/california/tuolumne-county/historic-preservation) — referral and commission process for H/HDP
Tuolumne County Design Review (/us/california/tuolumne-county/design-review) — design review processes tied to historic overlays
Tuolumne County Variances and Exceptions (/us/california/tuolumne-county/variances-and-exceptions) — for relief where overlays allow Director/Commission discretion
Tuolumne County Landscaping and Screening (/us/california/tuolumne-county/landscaping-and-screening) — where director can reduce requirements in H/HDP
California Building Standards Code (/us/california/building-codes) — referenced for foundation requirements in :MX and for State Historical Building Code application
California ADU law (/us/california/california-adu-laws) — Not found in retrieved materials: no explicit overlay/ADU cross-reference in Title 17; verify with County.

Information Gaps

The uploaded ordinance text references Exhibits A and B for the Airport Combining District boundaries but the actual maps/Exhibits were not included in the retrieved materials. Verify parcel mapping with County GIS / Planning. § 17.20.050(C)
No complete list of parcels currently zoned H or HDP was included; the ordinance describes criteria and procedure but not the current inventory. Verify with Historic Preservation / Planning. § 17.20.030(A)
No explicit guidance in the retrieved Title 17 excerpts about how combining districts interact with statutory ADU ministerial rules — local application is not shown; verify with the County and California ADU law. Not found in retrieved materials.

Sources

Retrieved passages

Tuolumne County Zoning Code (§ 4) High relevance
Tuolumne County Zoning Code Medium relevance
Tuolumne County Zoning Code (Chapter lists) Medium relevance
Tuolumne County Zoning Code (Chapter is) Medium relevance
Tuolumne County Zoning Code Medium relevance
Tuolumne County Zoning Code (Chapter shall) Medium relevance
CBC § 17.20.030 (Section 17.20.030) Medium relevance
Tuolumne County Zoning Code (Section 15331) Medium relevance

Cited sections

Tuolumne County Uniform Zoning Ordinance (Title 17) — Combining Districts: **§ 17.20.010** (Purpose) (Title 17)
Tuolumne County Uniform Zoning Ordinance — **Historic Combining District** **§ 17.20.020** (§ 17.20.020)
Tuolumne County Uniform Zoning Ordinance — **Historic Design Preservation (HDP)** **§ 17.20.030** (§ 17.20.030)
Tuolumne County Uniform Zoning Ordinance — **Mobile Home Foundation (:MX)** **§ 17.20.040** (§ 17.20.040)
Tuolumne County Uniform Zoning Ordinance — **Airport Combining (:AIR)** **§ 17.20.050** (§ 17.20.050)
Tuolumne County zoning & planning overview (/us/california/tuolumne-county) — context and county web resources
Tuolumne County Zoning (/us/california/tuolumne-county/zoning) — base zoning chapters and maps
Tuolumne County Land Use (/us/california/tuolumne-county/land-use) — ALUCP and related land-use materials
Tuolumne County Development Standards (/us/california/tuolumne-county/development-standards) — for standards referenced by combining districts
Tuolumne County Parking (/us/california/tuolumne-county/parking) — parking standards and in‑lieu options referenced in H/HDP
Tuolumne County Historic Preservation (/us/california/tuolumne-county/historic-preservation) — referral and commission process for H/HDP
Tuolumne County Design Review (/us/california/tuolumne-county/design-review) — design review processes tied to historic overlays
Tuolumne County Variances and Exceptions (/us/california/tuolumne-county/variances-and-exceptions) — for relief where overlays allow Director/Commission discretion
Tuolumne County Landscaping and Screening (/us/california/tuolumne-county/landscaping-and-screening) — where director can reduce requirements in H/HDP
California Building Standards Code (/us/california/building-codes) — referenced for foundation requirements in :MX and for State Historical Building Code application
California ADU law (/us/california/california-adu-laws) — Not found in retrieved materials: no explicit overlay/ADU cross-reference in Title 17; verify with County. (Title 17)
TuolumneCounty_ZoningCode.md

Frequently asked questions

What is a combining (overlay) district in Tuolumne County?

A combining district in Tuolumne County is an overlay that sits on top of the base zoning and modifies or supplements the base rules (e.g., altering permit requirements, parking, setbacks, or height limits) for parcels in unincorporated areas. See the general combining‑district purpose in § 17.20.010.

What does the Historic Combining District (H) change about my property?

The H district preserves individual historic resources; uses remain those of the underlying zone, but many development standards (setbacks, height, landscaping, parking) may not apply unless a use permit is secured. The State Historical Building Code may be used. See § 17.20.020.

How does the Historic Design Preservation (HDP) district affect parking and design review?

For HDP, underlying uses remain, but exterior changes typically require a use permit and Historic Preservation review; commercial parcels are given a special parking ratio of one space per 250 sq ft, with off‑site parking or in‑lieu fees allowed under certain conditions. See § 17.20.030(C).

If my parcel is in an Airport Combining (:AIR) district, what limits should I expect?

Expect to follow the ALUCP compatibility-zone rules: density and use restrictions, strict height limitations in critical zones (referencing FAR Part 77 and Chapters 18.24/18.28), and possible prohibition of uses that attract birds, create glare, or interfere with flight. Check the ALUCP maps and § 17.20.050.

Do combining districts change base zoning uses (e.g., allow new commercial uses)?

Generally, combining districts do not change the underlying allowed uses—the base zoning still controls uses unless the combining district expressly prohibits or conditions specific uses (common in the Airport Combining District). Always read the specific combining-district § and the underlying zone’s use table. See § 17.20.010–050.

Are mobile homes allowed anywhere with the :MX overlay?

Within a Mobile Home Foundation Combining (:MX) District, mobile/manufactured homes may be used on individual parcels only if installed on an approved foundation and meeting skirting and age requirements set out in § 17.20.040; mobile home parks are regulated separately. See § 17.20.040.

Can the County reduce landscaping or parking requirements in a historic district?

Yes—Title 17 authorizes the Director to reduce minimum required landscape area and to allow off‑site parking or in‑lieu fees in H and HDP districts under specified conditions, but often only after discretionary review. See § 17.20.020(C) and § 17.20.030(C)(2).

How do overlay districts interact with design review?

Design review and historic preservation processes commonly apply when an overlay like H or HDP is present; the ordinance requires referral to the Historic Preservation Review Commission and design compliance as part of discretionary approvals. See § 17.20.020(E)–(I) and § 17.20.030(E).

What if my parcel lies in two airport compatibility zones?

The code treats a parcel split by compatibility zone boundaries as if it were multiple parcels for density purposes; it also allows for density transfer from more restrictive to less restrictive zones under specified conditions. Check § 17.20.050(D) and consult the ALUCP and Planning for the parcel‑level interpretation.

Who do I contact to confirm whether an overlay applies to my parcel?

Confirm overlay status and obtain applicable maps from Tuolumne County Planning / GIS. The ordinance references Exhibits and maps (e.g., for the Airport Combining District) but the parcel‑level mapping is maintained by the County — Verify with the jurisdiction. § 17.20.050(C)

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