Local zoning · San Mateo County

San Mateo County — Overlay Districts

Q: Do I need a Coastal Development Permit for work in the CD overlay?

Possibly — the ordinance requires a Coastal Development Permit for projects defined in the CD rules; check § 8.252.050 for permit requirements and consult the Coastal Policy Checklist referenced in § 8.252.040(f) .

Q: Where do I find whether my parcel is in an S‑district, AO, CD, DR, GH or E overlay?

The County’s Zoning Maps and the district index (see § 8.08.030 and the S‑district table) list and map the combining districts and overlays; confirm parcel status with the County Planning Division since the map attachments (e.g., airport hazard map) are referenced in the ordinance but not reproduced here .

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

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Last reviewed: July 3, 2026

Overview

Overlay districts in the San Mateo County Zoning & Development Code are mapped, additional layers that apply on top of an underlying base zone in the County’s unincorporated areas. Overlays can add special use controls, require extra studies or permits, or impose stricter standards (for example for the Coastal Zone, geologic hazards, airport approaches, design review, or entertainment uses). The rules below summarize the County’s actual overlay districts, what they require, and where to look in the County code to confirm parcel‑specific rules. For the County’s broader zoning context see San Mateo County Zoning and for applicable development rules see San Mateo County Development Standards.

How to read this page

Every requirement below is grounded to the County ordinance by the controlling code section(s) (bold § cites). Each such statement is supported by the uploaded San Mateo County ordinance excerpts. Verify parcel-specific maps or up-to-date amendments with the County before filing: Verify with the jurisdiction.

District-by-district breakdown

Coastal Development Overlay — CD

Purpose: Implement the California Coastal Act within San Mateo County’s unincorporated Coastal Zone; the CD is an overlay that applies in addition to the underlying zone’s rules. See § 8.252.020 and § 8.252.030 .
Typical permitted uses: Uses allowed by the underlying district continue to be allowed unless the CD requires a specific permit; certain projects in the CD also require a Coastal Development Permit in addition to ordinary permits (see § 8.252.050) .
Key procedural/decision standards:
- Projects in the CD must comply with the Local Coastal Program and may be appealable to the Coastal Commission when specific criteria apply; see § 8.252.040(s) and § 8.252.050 .
- The ordinance defines “overlay district” and clarifies that overlay rules apply in addition to the underlying zone (see § 8.252.040(o)) .
Where it applies: The CD is coterminous with the County’s unincorporated Coastal Zone (i.e., only unincorporated areas) as mapped in the Local Coastal Program; see § 8.252.030 .
Practical note: Coastal permits often add special noticing, LCP policy checklists, and conditions — incorporate Coastal requirements into design and parking calculations early (see San Mateo County Parking and San Mateo County Development Standards).

Geologic Hazards Overlay — GH

Purpose: Regulate development in areas designated hazardous for geologic reasons to safeguard life and property; the GH is explicitly an overlay (see § 8.264.010 and § 8.264.020) .
Typical permitted uses: Land use and density are generally set by the underlying zone unless the GH is more restrictive; then the GH controls (see § 8.264.030) .
Key technical / submittal requirements:
- A district-specific geotechnical report prepared by a certified engineering geologist is required prior to designation of a GH area and is used to set development standards for that numbered GH district (see § 8.264.040) .
- No building permit may be approved until the County Geologist evaluates and approves the project per § 8.264.050; recording of deed restrictions can be required (see § 8.264.050(2)) .
Where it applies: GH districts are mapped and numbered; each has district-specific standards based on geotechnical findings (see § 8.264.020 and § 8.264.040) .
Practical note: The geotechnical conclusions become binding standards for the parcel; a GH overlay can effectively reduce developable density or require specialized mitigation — include geotechnical scope in early feasibility work.

Airport Overlay — AO / Half Moon Bay Airspace regulations (Chapters 8.248 and 8.356)

Purpose: Limit people density and hazardous development near airport runways and regulate airspace/shadow hazards around Half Moon Bay Airport (see § 8.248.020 and § 8.356.010) .
Typical permitted uses: Under the AO, all underlying permitted uses are allowed except certain residential uses or uses that allow more than three persons on site without a use permit (see § 8.248.030) .
Key dimensional / performance standards:
- New development must meet underlying district development standards; noise insulation / acoustical study is required to meet an interior CNEL 55 dBA standard (see § 8.248.040 and § 8.248.060) .
- The Half Moon Bay airport approach/conical/transitional/horizontal zones and height limits are mapped and defined in Chapter 8.356; strict height restrictions and permit/variance procedures apply (see § 8.356.030, § 8.356.040, § 8.356.070) .
Where it applies: Mapped approach and obstruction zones around Half Moon Bay Airport; a map dated in the ordinance (Half Moon Bay Airport Hazard Zoning Map) is part of the regulation (see § 8.356.030) .
Practical note: If your parcel falls inside an AO/airport zone, expect acoustic studies, possible use permits, and close review of height/trees; see San Mateo County Parking and San Mateo County Development Standards for site planning implications.

Entertainment Overlay — E

Purpose: Control operation and location of high‑impact uses (bars, clubs, card rooms, and meeting halls) where those uses have had detrimental impacts; the E is explicitly an overlay (see § 8.272.010 and § 8.272.040) .
Typical permitted uses: Bars, clubs, card rooms, meeting halls are not permitted except by obtaining a use permit; existing pre‑1982 operators had a limited window to apply (see § 8.272.050) .
Key standards: Where E conflicts with underlying district, E regulations take precedence (see § 8.272.040) .
Where it applies: Applied to discrete mapped areas — check Zoning Maps and the zoning index for an E overlay occurrence (see § Districts list: AO, CD, DR, GH, E) .
Practical note: Expect a use permit process with findings addressing nuisance, hours, and impacts; coordinate early with County planning and look at parking impacts (San Mateo County Parking).

Design Review Overlay — DR

Purpose: Preserve and enhance neighborhood character and site design by reviewing exterior construction, grading and tree removal in mapped Design Review (DR) districts (see § 8.256.010) .
Typical scope: Applies to all new exterior construction requiring a building permit, grading that needs a permit, or tree cutting requiring a permit — exemptions exist and the Design Review Administrator (DRA) can grant them (see § 8.256.030–.040) .
Key process/standards:
- A pre-design conference is required for projects in a DR district (see § 8.256.050) and the application must include detailed plans (see § 8.256.060) .
- Design Review standards and guidelines are applied by the DRA, Design Review Committee, or Planning Commission depending on the project and district.
Where it applies: Mapped DR districts (including some coastal Midcoast parcels where the DR rules apply only to residential development in RM‑CZ/PAD) — see § 8.256.010(B) for midcoast qualifications .
Practical note: Design review can drive form, materials, tree replacement and landscaping requirements (see San Mateo County Landscaping and Screening).

Special / Residential Density Districts — S‑xx (combining districts)

Purpose: Numbered “S” districts (e.g., S‑72, S‑93, etc.) are combining or special districts that modify density, lot standards, or other rules for particular neighborhoods; the zoning index shows these S districts and identifies which base zones are combined (see the district index and § 8.08.030) .
Typical effect: An S district changes permitted densities, minimum parcel sizes, or zoning relationships for the mapped area; where an S district is combined with a base zone the combined regulations apply (see § 8.08.030 and the S‑district index) .
Practical note: Always check the parcel’s Zoning Map and the specific S‑district text (some S districts are referenced in other chapters) — Verify with the jurisdiction.

Decision‑relevant standards at a glance

Overlay	Most relevant action(s) required	Typical quantitative standard or trigger	Code reference
CD (Coastal)	Apply for Coastal Development Permit when project meets CD thresholds; complete Coastal Policy Checklist	CD maps = Coastal Zone; CD rules apply in addition to base zone	§ 8.252.020, § 8.252.030, § 8.252.050
GH (Geologic)	Submit geotechnical report; County Geologist review; may require deed restriction	District-specific technical standards set by geotech report	§ 8.264.020–.050
AO (Airport)	Acoustical study; check permitted uses; permit for trees/structures above heights	Interior CNEL ≤ 55 dBA; mapped approach/transition/horizontal/conical zones; strict height limits	§ 8.248.060, § 8.356.030–.040
E (Entertainment)	Use permit required for bars/clubs/card rooms; stricter operational controls	Use permits; overlay takes precedence where conflict	§ 8.272.040–.050
DR (Design Review)	Pre-design conference; design review application & plans; possible tree protection/replacement	Application content requirements listed; exemptions possible	§ 8.256.030–.060

(See San Mateo County Design Review for process details and San Mateo County Parking for parking impacts.)

Checklist

Confirm whether the parcel is in an overlay on the County Zoning Map (verify CD, GH, AO, DR, E, or S‑district status) — see § 8.08.030 .
If in CD, determine if a Coastal Development Permit is required and prepare the Coastal Policy Checklist — § 8.252.050 .
If in GH, order a geotechnical report meeting the County’s Minimum Standards and plan for County Geologist review and possible deed restrictions — § 8.264.040–.050 .
If in AO or near Half Moon Bay Airport, obtain the required acoustical analysis (CNEL 55 interior target) and check height/tree restrictions and permitting — § 8.248.060, § 8.356.040 .
If in DR, schedule a pre‑design conference with the Design Review Administrator and prepare the full submission set required by § 8.256.060 .
For E districts, plan for a use permit and conditions addressing hours, nuisance and operations — § 8.272.050 .
Confirm parking, setback and lot coverage rules of the underlying zone and any overlay‑specific overrides (consult San Mateo County Parking and San Mateo County Development Standards).
Verify whether any proposed ADU or accessory changes trigger additional Coastal, GH, or DR review (see § 8.396.130 for CD applicability) .

Risks & Ambiguities

Issue	Why it matters	What to verify
Overlay vs underlying conflict	Some overlays (e.g., E) explicitly take precedence when they conflict with the base zone (§ 8.272.040)	Confirm which standard governs the parcel and read the overlay chapter text for conflict rules
Exact overlay map boundaries	Ordinance references maps (e.g., Airport hazard map, Coastal Zone) but the map sheet itself and parcel‑level application may be updated	Obtain the current County Zoning Map and any attached hazard maps (Half Moon Bay Airport map is referenced in § 8.356.030)
Technical report scope	GH requires geotech reports that become the binding standards; inadequate scope => rework	Confirm County “Minimum Standards for Geotechnical Reports” and scope references in § 8.264.040
CD appealability to Coastal Commission	Some approvals in the CD are appealable; applicants may assume local approval is final	Check § 8.252.040(s) for project types that may be appealable and build time for potential appeals into schedule
Noise metric and thresholds for AO	Developers may rely on base zoning for interior noise expectations; AO adds CNEL 55 dBA requirement	Confirm acoustical study standards and consultant qualifications per § 8.248.060
Applicability to ADUs	ADU rules have statewide overrides and special coastal applicability; overlay may impose extra approvals	See § 8.396.130 for ADU applicability in the Coastal Zone; Verify with the jurisdiction for overlay interactions

Plain-English Summary

If your property is in an unincorporated part of San Mateo County, overlays like CD, GH, AO, DR, and E are extra zoning layers that add permits, studies, or stricter rules on top of the base zone; check the exact overlay chapter cited (for example § 8.252 for Coastal, § 8.264 for Geologic Hazards, § 8.248 and § 8.356 for Airport rules, § 8.256 for Design Review) and obtain any required reports before you design the project. See San Mateo County Design Review for review steps and San Mateo County Parking for parking impacts.

Information Gaps

Parcel‑level overlay boundaries (Zoning Map and attached hazard maps): Not included in the retrieved text — Verify with the County.
The County’s current “Minimum Standards for Geotechnical Reports” document referenced by § 8.264.040: Not included in the retrieved materials — Verify with the County Geologist. .
The actual Half Moon Bay Airport Hazard Zoning Map sheet (attached by the ordinance) is referenced but not included in the retrieved file — Verify with County Public Works (see § 8.356.030) .
Any ordinance amendments adopted after the provided excerpts: Not found in retrieved materials — Verify with the County Clerk/Planning Division.

Source References

San Mateo County Zoning & Development Code — Coastal Development (CD): § 8.252.020, § 8.252.030, § 8.252.050, definitions § 8.252.040(o) .
San Mateo County Zoning & Development Code — Geologic Hazards (GH): § 8.264.010, § 8.264.020, § 8.264.030, § 8.264.040, § 8.264.050 .
San Mateo County Zoning & Development Code — Airport Overlay (AO): § 8.248.010–.060 (AO chapter) .
San Mateo County Zoning & Development Code — Height/Airspace near Half Moon Bay Airport: § 8.356.010–.110 (airport zones, maps, height limits, permits) .
San Mateo County Zoning & Development Code — Entertainment Overlay (E): § 8.272.010–.050 .
San Mateo County Zoning & Development Code — Design Review (DR): § 8.256.010–.060 (establishment, requirements, pre‑design conference, application contents) .
San Mateo County Zoning & Development Code — District index and combining S‑district list: § 8.08.030 and district table (shows AO, CD, DR, GH, E, S‑xx) .
San Mateo County Zoning & Development Code — Special setback lines: § 8.352.010–.030 (special building setback lines) .
San Mateo County Zoning & Development Code — ADU Coastal applicability: § 8.396.130 .

Sources

Retrieved passages

San Mateo County Zoning Code (Section 30107) High relevance
San Mateo County Zoning Code (Chapter shall) High relevance
San Mateo County Zoning Code (Chapter 8.276) High relevance
San Mateo County Zoning Code (Section 4511) High relevance
San Mateo County Zoning Code (Title 8) Medium relevance
San Mateo County Zoning Code (Title 8) Medium relevance
San Mateo County Zoning Code (Title 8) Medium relevance
San Mateo County Zoning Code (§ 6541.4) Medium relevance
San Mateo County Zoning Code (Chapter shall) High relevance
San Mateo County Zoning Code (§ 6303) Medium relevance
San Mateo County Zoning Code (Title 8) Medium relevance
San Mateo County Zoning Code (Title 8) Medium relevance
San Mateo County Zoning Code (§ 6111) Medium relevance
San Mateo County Zoning Code (section shall) Medium relevance

Cited sections

Official San Mateo County code library

Frequently asked questions

What is the Coastal Development (CD) overlay and when does it apply in San Mateo County?

The CD overlay implements the California Coastal Act for San Mateo County’s unincorporated Coastal Zone; it applies in addition to the parcel’s underlying zone and is coterminous with the County’s mapped Coastal Zone (see § 8.252.020 and § 8.252.030) .

Do I need a Coastal Development Permit for work in the CD overlay?

Possibly — the ordinance requires a Coastal Development Permit for projects defined in the CD rules; check § 8.252.050 for permit requirements and consult the Coastal Policy Checklist referenced in § 8.252.040(f) .

What triggers a geotechnical report in a GH overlay area?

In a GH district a geotechnical report prepared by a certified engineering geologist is required prior to designation or for permit review and the geotechnical conclusions become the district standards; see § 8.264.040 and § 8.264.050 .

If my property is inside an Airport Overlay (AO), what special studies are required?

New development in the AO typically requires an acoustical analysis demonstrating interior CNEL ≤ 55 dBA and must comply with mapped airport approach/height limits; see § 8.248.060 and § 8.356.030–.040 .

Will Design Review (DR) apply to small additions or ADUs?

Design Review applies to new exterior construction, grading that needs a permit, and tree cutting in DR districts unless the Design Review Administrator finds the activity exempt; see § 8.256.030–.040. ADUs in coastal areas have special rules — see § 8.396.130 for Coastal applicability of ADU regulations .

Can an overlay require a deed restriction or other recorded instrument?

Yes — the GH district in particular may require recording of deed restrictions that bind successors as part of the building permit approval process (see § 8.264.050(2)) .

Do overlay rules ever override the underlying zone?

Yes — some overlays (for example the E overlay) state that where E conflicts with the underlying district, the E regulations take precedence (see § 8.272.040) .

Where do I find whether my parcel is in an S‑district, AO, CD, DR, GH or E overlay?

The County’s Zoning Maps and the district index (see § 8.08.030 and the S‑district table) list and map the combining districts and overlays; confirm parcel status with the County Planning Division since the map attachments (e.g., airport hazard map) are referenced in the ordinance but not reproduced here .

If I want to build an ADU, how do overlays affect that process?

ADU rules are governed by Title 8 ADU chapter but ADUs in the Coastal Zone and in overlay districts may require additional permits or be subject to overlay standards; see the ADU coastal applicability § 8.396.130 and verify overlay interactions with County planning .

Who enforces airport height limits and what are the appeal options?

The Director of Planning and Building enforces airport height/airspace regulations in Chapter 8.356; permits/variances are processed by the Director with appeals to the Planning Commission and then to the Board of Supervisors (see § 8.356.080–.100) .

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