Chapter 8.396 — ACCESSORY DWELLING UNITS, COASTAL ZONE

San Mateo County, California, Code of Ordinances Title 8 – Zoning & Development Code

Accessory dwelling units are a residential use that provide an important source of housing. The purpose of this Chapter is to:

1. Increase the supply and diversity of the County’s housing stock, in particular the number of smaller and more affordable units, by allowing accessory dwelling units to be built on existing residential properties, while preserving the neighborhood character.

2. Increase the housing stock of existing neighborhoods in a manner that has less impact on the environment than development of housing in undeveloped areas.

3. Allow more efficient use of existing residential areas and supporting infrastructure.

4. Provide a means for residents to remain in their homes and neighborhoods.

5. Provide opportunities for homeowners to earn supplemental income from renting an accessory dwelling unit.

6. Establish standards for accessory dwelling units in the County’s Coastal Zone to ensure that they are safe, habitable, compatible with existing development, and consistent with the policies of the County’s Local Coastal Program and the California Coastal Act.

1. Primary Residence. A “primary residence” is the main residence located or proposed to be located on the parcel on which an accessory dwelling unit(s) is located or proposed to be located.

2. Accessory Dwelling Unit. An “accessory dwelling unit” is a dwelling unit located or proposed to be located on a lot which contains, or will contain, a primary residence. Accessory dwelling units may be detached from or attached to the primary residence on the property. Accessory dwelling units may also be (1) efficiency units, as defined in Section 17958.1 of the California Health and Safety Code, or (2) manufactured homes, as defined in Section 18007 of the California Health and Safety Code. Accessory dwelling units are “accessory dwelling units” as that term is used in Government Code Section 65852.2. An accessory dwelling unit includes an efficiency unit as defined in Section 17958.1 of the Health and Safety Code or a manufactured home as defined in Section 18007 of the Health and Safety code. A “second unit” or “secondary unit” is an accessory dwelling unit. Accessory dwelling units are not “accessory buildings” as defined in Section 6102.19. Any secondary structure that provides independent facilities for living; sleeping; eating; cooking; and sanitation, may be considered an accessory dwelling

San Mateo County, California, Code of Ordinances Title 8 – Zoning & Development Code

unit, at the discretion of the Director of Planning and Building, unless an applicant can provide compelling evidence to the contrary to the satisfaction of the Director of Planning and Building.

3. Detached Accessory Dwelling Unit. A “detached accessory dwelling unit” is a unit that is an independent structure, entirely separated from the structure of the primary residence. Accessory dwelling unit constructed within, or as an extension of an existing detached structure other than the primary residence are considered detached accessory dwelling units.

4. Attached Accessory Dwelling Unit. An “attached accessory dwelling unit” is a unit that is built as an addition to, extension of, or within the primary residence.

5. Junior Accessory Dwelling Unit. A “junior accessory dwelling unit” is an accessory dwelling unit built entirely within the walls of an existing or proposed primary residence, not exceeding five hundred sq. ft. in size, and including an efficiency kitchen, as described in Government Code Section 65852.22. A junior accessory dwelling unit may include separate sanitation facilities or may share sanitation facilities with the existing structure or unit.

6. Efficiency Kitchen. An efficiency kitchen, as defined in Government Code Section 65852.22, is a kitchen that contains at least a cooking facility with appliances, and a food preparation counter and storage cabinets that are of reasonable size in relation to the size of the junior accessory dwelling unit.

7. Floor Area. For purposes of this Chapter, the “floor area” of an accessory dwelling unit is the area of each floor level included within the walls enclosing each dwelling unit. The floor area shall be measured from the outside face of the walls enclosing each dwelling unit including all closet space and storage areas contained within the unit, including habitable basements and attics, but not including unenclosed porches, balconies, or any enclosed garages or carports. For purposes of calculating allowable floor area of accessory dwelling units based on a proportion of the size of the primary residence, only the livable floor area of the primary residence shall be counted. The floor area of any other structures, for purposes of calculating total floor area, lot coverage, or other calculations, shall be calculated in the manner described in the relevant zoning regulations.

8. Owner Occupancy. Owner occupancy is the condition and requirement that the owner of a parcel on which a junior accessory dwelling unit is constructed live in one of the units on the property in perpetuity.

9. Stepback. A setback above the ground floor, where the building is “stepped back” an additional distance from the outermost point of the building at the ground level.

Accessory dwelling units shall be allowed in the R-1, R-2, and R-3 Zoning Districts in the County’s Coastal Zone, regardless of any regulations that might otherwise prohibit accessory dwelling units in any specific district.

San Mateo County, California, Code of Ordinances Title 8 – Zoning & Development Code

Accessory dwelling units meeting all of the applicable requirements of Sections 8.396.050 through 8.396.090, as applicable, shall be approved ministerially, without public notice, public hearing, or discretionary review, in the manner and to the extent described in Section 6439.17.

Accessory dwelling units not meeting the applicable standards set forth in Sections 8.396.050 through 8.396.090 will be considered a conditionally permitted use within the districts specified in Section 8.396.030 and may be permitted by a conditional use permit pursuant to a public hearing before the Zoning Hearing Officer, as described in Section 8.396.110 Conditionally permitted units may also still be subject to other permitting requirements and approvals pertaining to the County’s Coastal Zone, as described in Section 8.396.180.

New accessory dwelling units shall be subject to the requirements and standards described in this chapter. Where not superseded by the specific requirements described in this chapter, accessory dwelling units shall also be subject to the requirements applicable to any dwelling unit on the same parcel in the same district. Development standards applicable to all accessory dwelling units include the following:

1. Minimum Lot Area. Accessory dwelling units shall be exempt from the minimum lot area per dwelling unit provisions in the applicable district.

2. Minimum Lot Size. Accessory dwelling units shall be exempt from all minimum lot size requirements.

3. Maximum Density of Development. Accessory dwelling units shall be exempt from any and all provisions limiting the maximum density of development in the applicable district.

4. Setbacks. Notwithstanding the required setbacks in the applicable district, minimum setbacks for accessory dwelling units shall be:

a. Front Setbacks. With the exception of accessory dwelling units created entirely within the space of an existing structure, for all other accessory dwelling units regardless of height, the accessory dwelling unit may be located no closer to the front property line of the subject parcel than the lesser of:

• (1) The front setback required by the relevant zoning district, or

San Mateo County, California, Code of Ordinances Title 8 – Zoning & Development Code

(2) The distance from the front property line of the primary residence located or proposed to be located on that parcel. For purposes of this section, the primary residence includes attached garages.

In cases where an existing primary residence is closer to the front property line than the front setback normally required in the same district, the accessory dwelling unit shall also be allowed to be located as close to the front property line as the primary residence.

In cases where an accessory dwelling unit is proposed to be built atop an existing detached garage that is located within the required front setback, a conditional use permit shall be required.

b. Side and Rear Setbacks. For accessory dwelling units created entirely within the space of an existing structure, setbacks shall be those already existing for that structure, unless such setbacks present demonstrable safety issues.

For all other accessory dwelling units regardless of height, the accessory dwelling unit may be located no closer to the property line than: Side: 4 feet; Rear: 4 feet.

c. Stepbacks. Accessory dwelling units, whether attached or detached, exceeding 16 feet in height shall have the following stepbacks, located at a point no higher than 16 feet on the structure: Side: 5 feet; Rear: 10 feet.

5. Floor Area. The allowable floor area of an accessory dwelling unit shall be calculated in the manner described in Sections 8.396.050 through 8.396.090, but in no case shall these regulations be applied in such a way as to preclude an attached or detached accessory dwelling unit of at least 800 sq. ft. in size that meets all other relevant standards.

6. Lot Coverage. Accessory dwelling units shall count against the allowed lot coverage on a parcel, except that no lot coverage restriction shall preclude creation of an attached or detached accessory dwelling unit of at least 800 sq. ft. in size that meets all other relevant standards.

7. Height. The maximum height of the accessory dwelling unit shall be twenty-six feet. Building height shall be measured as the vertical distance from any point on the lower of (a) finished grade, or (b) natural grade, to the topmost point of the building immediately above. Chimneys, pipes, mechanical equipment, antennae, and other similar structures may extend up to eight feet beyond the building height, as required for safety or efficient operation. Accessory dwelling units built entirely within an existing building shall be subject to the greater of the height limit applicable to that building in the relevant district, or the maximum height of the existing primary residence, measured in the manner described in the Zoning Regulations of the relevant district.

San Mateo County, California, Code of Ordinances Title 8 – Zoning & Development Code

8. Daylight Plane. Neither accessory dwelling units built above an existing detached or attached garage or accessory structure, nor detached accessory dwelling units taller than sixteen (16) feet in height, shall be subject to daylight plane requirements.

9. Balconies and Decks. Accessory dwelling units that do not meet the setback requirements that would apply to a primary residence in the same district shall have no rooftop decks, and no portion of any balcony or deck shall be located above ten (10) feet in height, exclusive of railings, measured in the same manner as height in Section 6439.7, except on the side of the accessory dwelling unit facing the primary residence. Accessory dwelling units that meet the setback requirements that would apply to a primary residence in the same district may have rooftop decks and balconies to the extent otherwise allowed in the relevant district.

10. Windows. Accessory dwelling units that do not meet the setback requirements that would apply to a primary residence in the same district shall have no windows located above or extending above ten (10) feet on the accessory dwelling unit, measured from finished grade, except on: (1) the side(s) of the accessory dwelling unit facing the primary residence, and (2) the side(s) of the accessory dwelling unit that comply with the normal setback requirements of the district. On the sides of the accessory dwelling unit that do not meet the normal setback requirements of the district, clerestory windows located above ten (10) feet on the accessory dwelling unit shall be allowed, if they have a lower sill height of no less than six feet from the nearest interior floor of the accessory dwelling unit, and a total window height no greater than twenty-four (24) inches. Skylights shall be allowed.

11. Ingress and Egress. Accessory dwelling units shall have an independently accessible entrance that does not require passage through the primary residence.

12. Required Facilities. With the exception of junior accessory dwelling units, which are subject to the requirements described in Section 6439.8, all attached or detached accessory dwelling units must include the following:

• a. Independent facilities for living, sleeping, eating, cooking, and sanitation.

b. A kitchen area containing a refrigerator, sink, and permanently installed cooking appliance, which must include at least a fixed stovetop.

• c. A fully plumbed bathroom including sink, shower, and toilet.

13. Parking Requirements

a. Required Parking. Parking for accessory dwellings units shall be provided as follows:

San Mateo County, California, Code of Ordinances Title 8 – Zoning & Development Code

• (1) Outside of the designated areas shown in LCP Maps 3.1, “ADU Parking Area – Montara and Moss Beach,” and 3.2, “ADU Parking Area – El Grenada and Pillar Point Harbor,” one new covered or uncovered parking space, in addition to those already existing on the parcel, shall be provided on-site for each new attached or detached accessory dwelling unit, unless the accessory dwelling unit meets the parking exemption criteria of subsection b. below. When a garage, carport, or covered parking structure is demolished in conjunction with the construction of an accessory dwelling unit or converted to an accessory dwelling unit outside of such designated areas, those off-street parking spaces are not required to be replaced.

• (2) Within the designated areas shown in LCP Maps 3.1 and 3.2, at least one off-street parking space shall be required for each accessory dwelling unit, and all off-street parking requirements associated with other residential uses at the site shall be met onsite, including replacement parking spaces if any are removed or converted to accommodate an accessory dwelling unit.

• b. Parking Exemptions. Accessory dwelling units located outside of the designated areas shown in LCP Maps 3.1 and 3.2 and meeting any of the following criteria shall not be required to provide any parking in addition to that already provided on the parcel, or in the case of a concurrent application for a new primary and accessory dwelling unit, shall not be required to provide any parking in addition to the parking required for the primary residence:

  • (1) Accessory dwelling units located within one-half (1/2) mile of a public transit stop or station, measured as a direct line from the transit stop. Public transit stops must be served by a transit line serving the public, and not solely by specialized, private, or limited population services such as school buses, privately run shuttles, or other services that cannot be used by all public riders.

  • (2) Accessory dwelling units located within a designated architecturally and historically significant historic district.

  • (3) Accessory dwelling units that are part of the existing primary residence or an existing accessory structure, including attached or detached garages.

  • (4) Accessory dwelling units located within one (1) block of a car share vehicle pick-up/drop-off location.

• c. Conversion of Covered Parking. Any covered parking removed in order to create an accessory dwelling unit, if required to be replaced, may be replaced with uncovered parking of any type and configuration allowed by Section 8.396.050(13)(f), below. For purposes of this Section, conversion includes partial or full demolition of covered parking required to create an accessory dwelling unit.

• d. Garage conversion. If an existing attached or detached garage is converted to an accessory dwelling unit, the parking previously provided by that garage may be replaced by uncovered

San Mateo County, California, Code of Ordinances Title 8 – Zoning & Development Code

parking of any type and configuration allowed by Section 8.396.050(13)(f), below, and no additional parking related to the accessory dwelling unit is required. For purposes of this Section, conversion includes partial or full demolition of the garage and partial or full replacement with an accessory dwelling unit.

e. Use of Existing Parking. If the parking already existing on the parcel exceeds that required for existing development on the parcel, excess parking spaces shall be counted toward the new parking required for the accessory dwelling unit.

• f. Provision and Location of Parking. Parking spaces shall be provided in the following manner:

(1) Pervious Surfaces. All new parking spaces created for the accessory dwelling unit must be provided on pervious surfaces. The maximum amount of impervious surfaces designated to satisfy the accessory dwelling unit parking requirement shall be no greater than the amount of impervious surfaces existing at time of application. Existing impervious surface area may be used for parking and need not be converted to pervious surface.

(2) Uncovered Parking. All parking required for the accessory dwelling unit may be uncovered.

(3) Front or Side Yard Parking. Up to three parking spaces may be provided in the front or side yard. Not more than 600 sq. ft. of the front yard area shall be used for parking.

(4) Tandem Parking. Required parking spaces for the primary residence and the accessory dwelling unit may be provided in tandem on a driveway. A tandem parking arrangement consists of one car behind the other. No more than three total cars in tandem may be counted toward meeting the parking requirement.

(5) Compact Spaces. All parking required for the accessory dwelling unit may be provided by compact parking spaces, as defined in Section 8.344.010(a).

14. Requests for Parking Exceptions. If the required parking for an accessory dwelling unit outside the designated areas shown in LCP Maps 3.1 and 3.2 cannot be met in accordance with this Chapter, an application may be submitted for a parking exception, as specified in Section 8.344.040. For parking provided in accordance with the provisions of this Chapter, a parking exception shall not be required.

uests for Parking Exceptions. If the required parking for an accessory dwelling unit outside the designated areas shown in LCP Maps 3.1 and 3.2 cannot be met in accordance with this Chapter, an application may be submitted for a parking exception, as specified in Section 8.344.040. For parking provided in accordance with the provisions of this Chapter, a parking exception shall not be required.

15. Design Review. Accessory dwelling units shall not be subject to design review, except to the extent that they are located in the County’s Coastal Zone. Accessory dwelling units in the County’s Coastal Zone are subject to relevant design review requirements incorporated in the County’s Local Coastal Program and Zoning Regulations, however, such units shall not be reviewed by a Design Review Committee, nor shall their design be subject to consideration at any public hearing. Compatibility with applicable design

San Mateo County, California, Code of Ordinances Title 8 – Zoning & Development Code

standards for such units shall be determined by the Director of Planning and Building or the Director’s designee.

16. Architectural Review. Accessory dwelling units located in scenic corridors in the County’s Coastal Zone shall be subject to architectural review as normally required.

17. Concurrent Application for Development of Primary Residence and Accessory Dwelling Unit. In the case of a concurrent application for development of a new primary residence and new accessory dwelling unit on the same parcel, whichever unit is first issued a certificate of occupancy must conform to all applicable regulations for the primary residence in the relevant district.

18. Conversion of Existing Residence. An existing residence may be converted to an accessory dwelling unit in conjunction with development of a new primary residence, if the existing residence, once converted, will meet all the standards applicable to development of a new accessory dwelling unit described in this Chapter.

19. Conversion of Accessory Buildings. An accessory dwelling unit may be constructed within or above an existing, detached accessory building, provided the resulting unit conforms to all applicable provisions of this Chapter.

Accessory dwelling units constructed within or above an existing, detached accessory building that conforms to all applicable provisions of this Chapter shall not be required to obtain a use permit, regardless of the requirements of the applicable district.

Accessory dwelling units built within or above existing garages are subject to the specific provisions of this Chapter regarding such units, regardless of any regulations to the contrary in the Zoning Regulations.

20. Creation of Accessory Dwelling Unit Entirely Within a Non-Conforming Primary Residence. In the case of an existing primary residence that does not conform to one or more zoning regulations, creation of an accessory dwelling unit that will be entirely within the existing primary residence shall not, in itself, create a requirement that the nonconformities be rectified. However, no other provisions that may require rectification of existing nonconformities are waived merely due to approval of an accessory dwelling unit, unless specifically described in this Chapter.

21. Short Term Rental. Accessory dwelling units created pursuant to the provisions of this Chapter, if rented, shall only be rented for a term longer than 30 days.

22. Impact Fees. Accessory dwelling units of less than 750 sq. ft. in size shall be exempt from all impact fees. Accessory dwelling units of greater than 750 sq. ft. in size shall only be charged impact fees in an amount equal to the standard impact fee for such a unit, multiplied by the proportion of the accessory dwelling unit to the primary dwelling unit.

San Mateo County, California, Code of Ordinances Title 8 – Zoning & Development Code

New detached accessory dwelling units shall be subject to the requirements described in Section 6439.5, and to the following requirements:

1. Distance between Detached Accessory Dwelling Units and Other Residential Structures. The distance required between a detached accessory dwelling unit and any other residential structure on the same parcel must be a minimum of five (5) feet, measured from foundation to foundation. If a separation distance greater than five (5) feet is required by any other section of the Zoning Regulations, it shall be disregarded, and the standards of this Chapter shall govern.

2. Floor Area of Detached Accessory Dwelling Units. Notwithstanding any floor area standards applicable to accessory dwelling units in the applicable district, the following floor area standards shall apply:

a. The floor area of a detached accessory dwelling unit shall not exceed eight hundred (800) sq. ft. or thirty-five percent (35%) of the livable floor area of the existing or proposed primary residence, whichever is larger, up to a maximum of one thousand five hundred (1,500) square feet. The floor area of the primary residence shall be calculated in the manner described in the relevant base or overlay district Zoning Regulations.

b. The floor area of a detached accessory dwelling unit shall count against the total floor area allowed on a parcel, such that the total floor area of the accessory dwelling unit in combination with the square footage of the primary residence and other structures on or proposed to be on the parcel shall not exceed the maximum floor area allowed within the zoning district, with the following exception:

(1) Regardless of floor area limitations, a single eight hundred (800) square foot detached accessory dwelling unit shall be allowed on a parcel, so long as that accessory dwelling unit can meet the setback and stepback requirements described in Section 6439.5.4.

3. Detached Accessory Dwelling Units and Junior Accessory Dwelling Units. One detached accessory dwelling unit may be built in combination with one junior accessory dwelling unit built on the same parcel, as long as both units comply with all relevant provisions of this Chapter.

New attached accessory dwelling units shall be subject to the requirements described in Section 6439.5, and to the following requirements:

San Mateo County, California, Code of Ordinances Title 8 – Zoning & Development Code

1. Floor Area of Attached Accessory Dwelling Units. Notwithstanding any floor area standards applicable to accessory dwelling units in the applicable district, the following floor area standards shall apply:

a. The floor area of an attached accessory dwelling unit shall not exceed eight hundred (800) sq. ft. or fifty percent (50%) of the livable floor area of the existing or proposed primary residence, whichever is larger, up to a maximum of one thousand five hundred (1,500) square feet. The floor area of the primary residence shall be calculated in the manner described in the relevant base or overlay district Zoning Regulations.

b. The floor area of an attached accessory dwelling unit shall count against the total floor area allowed on a parcel, such that the total floor area of the accessory dwelling unit in combination with the square footage of the primary residence and other structures on or proposed to be on the parcel shall not exceed the maximum floor area allowed within the zoning district, with the following exception:

(1) Regardless of floor area limitations, a single eight hundred (800) square foot attached accessory dwelling unit shall be allowed on a parcel, so long as that accessory dwelling unit can meet the setback and stepback requirements in Section 8.396.050(4).

(2) For attached accessory dwelling units built entirely within the walls of an existing or proposed primary residence, an additional one-hundred fifty (150) sq. ft. of floor area is allowed regardless of other floor area limitation, solely for the purpose of providing ingress/egress, and not for expanded living space. Such space for ingress and egress typically includes, but is not limited to, stairs, porches, foyers, and other similar areas.

2. Ingress and Egress for Attached Accessory Dwelling Units. With the exception of junior accessory dwelling units, attached accessory dwelling units shall only be allowed a connecting doorway or other permanent ingress or egress between the primary residence and the accessory dwelling unit with the approval of the Director of Planning and Building, at the Director's discretion. In all cases, such doorways must be independently securable from within the accessory dwelling unit and from within the primary residence. Junior accessory dwelling units are permitted to have a connecting doorway or other permanent ingress or egress between the primary residence and the junior accessory dwelling unit, but such doorway must also be independently securable from within both the junior accessory dwelling unit and the primary residence.

rable from within the accessory dwelling unit and from within the primary residence. Junior accessory dwelling units are permitted to have a connecting doorway or other permanent ingress or egress between the primary residence and the junior accessory dwelling unit, but such doorway must also be independently securable from within both the junior accessory dwelling unit and the primary residence.

For accessory dwelling units attached to the primary residence, any new entrances and exits may face the front of the parcel only if they are 1) located so as not to be visible from the front of the parcel, or 2) unless otherwise, required by clearance and or landing requirements, or 3) unless permitted by the Director of Planning and Building, at the Director’s discretion.

3. No Combining of Attached Accessory Dwelling Units and Other Accessory Dwelling Units.

San Mateo County, California, Code of Ordinances Title 8 – Zoning & Development Code

An attached accessory dwelling unit that does not meet the definition of, and comply with all relevant standards relating to, a junior accessory dwelling unit, may not be built in combination with any other attached or detached accessory dwelling unit on the same parcel.

New attached junior accessory dwelling units shall be subject to the requirements described in Section 8.396.050, with the following exceptions:

1. Location. Junior accessory dwelling units must be constructed entirely within the walls of an existing or proposed primary single-family residence, except that an additional one hundred fifty (150) sq. ft. may be built solely for the purpose of providing ingress and egress for the junior accessory dwelling unit.

2. Floor area. The floor area of a junior accessory dwelling unit may be no greater than five hundred (500) sq. ft. under any circumstance, except that an additional one-hundred fifty (150) sq. ft. may be created outside of the primary residence, solely for the purpose of providing ingress and egress for the junior accessory dwelling unit.

3. Required Facilities. Junior accessory dwelling units must have a sleeping area, sink, and efficiency kitchen as defined in Government Code Section 65852.22. JADUs may share a bathroom with the primary residence.

4. Internal Ingress and Egress. Junior accessory dwelling units must have external ingress and egress, as described in Subsection 8.396.050(11). However, junior accessory dwelling units may have internally connecting doorways between the junior accessory dwelling unit and the primary residence. The internally connecting doorway must be independently securable from both the junior accessory dwelling units and the primary residence.

5. Owner Occupancy. The owner(s) of the parcel on which a junior accessory dwelling unit is proposed shall be required to occupy one of the units on the parcel. The owner(s) shall be required to record a deed restriction enforcing this requirement, which shall run with the land, and which shall be provided to the Planning and Building Department. The deed restriction shall also include a prohibition on the sale of the junior accessory dwelling unit separate from the sale of the single-family residence, including a statement that the deed restriction may be enforced against future purchasers.

On parcels with existing multi-family structures, including multi-family structures with two or more units, multiple accessory dwelling units shall be allowed, subject to the requirements described in Section 8.396.050 and to the following requirements:

San Mateo County, California, Code of Ordinances Title 8 – Zoning & Development Code

1. Accessory Dwelling Units within Multifamily Structures:

a. Multiple accessory dwelling units may be created within the portions of existing multi-family dwelling structures that are not used as livable space, including, but not limited to, storage rooms, boiler rooms, passageways, attics, basements, or garages, if each unit complies with state building standards for dwellings.

b. A minimum of one accessory dwelling unit shall be allowed within an existing multi-family dwelling, and a maximum number of accessory dwelling units not exceeding twenty-five percent (25%) of the existing multi-family dwelling units on the parcel, if those accessory dwelling units meet all required standards of this Chapter.

2. Detached Accessory Dwelling Units on Parcels with Multifamily Structures. No more than two detached accessory dwelling units shall be allowed on a parcel that has an existing multi-family dwelling, subject to the provisions of this Chapter.

1. Building permits may be issued for existing accessory dwelling units which were constructed without required permits, under the following conditions:

a. The accessory dwelling unit conforms to all applicable provisions of this Chapter, and all other applicable required standards for habitability.

• b. All applicable fees for construction completed without permits have been paid.

Accessory dwelling units constructed without permits that do not meet the provisions of this Section may apply for a conditional use permit, as described in Section 8.396.110.

1. Accessory dwelling units not meeting all applicable standards of this Chapter may be conditionally permitted, subject to a conditional use permit.

2. With the exception of accessory dwelling units described in Section 8.396.110(4), below, the process for application for and issuance of a conditional use permit for an accessory dwelling unit shall be that set forth in Section 8.280.030 of the County Zoning Regulations, except that the granting of the permit shall

San Mateo County, California, Code of Ordinances Title 8 – Zoning & Development Code

be at the determination of the Zoning Hearing Officer. The determination of the Zoning Hearing Officer shall be appealable to the County Planning Commission only, subject to the procedures specified in Chapter 8.280 and Chapter 8.448 of the Zoning Regulations.

3. In the case of accessory dwelling units within the Coastal Zone which are proposed in conjunction with other development that is required to be reviewed by the Planning Commission, the conditional use permit will be reviewed and granted by the Planning Commission only, and shall not be appealable. The Planning Commission’s review may not consider issues related to design review.

4. Accessory dwelling units requiring a conditional use permit which are within the Coastal Development (CD) District may require a Coastal Development Permit that may be appealable to the Coastal Commission.

5. In the event that the creation or legalization of an accessory dwelling unit creates conflicts with standards specific to the base or overlay zoning of the parcel, or other standards for which specific exceptions are not provided in this Chapter, those conflicts must be addressed by whatever relief, if any, and through whatever procedures, are normally required by the regulations in which those standards are contained.

6. In the case of accessory dwelling units meeting all applicable standards of this Chapter except those related to parking requirements, a parking exception may be requested as provided in Section 8.396.050(14), and a conditional use permit shall not be required.

For accessory dwelling units that may be allowed contingent on approval of a Home Improvement Exception (HIE), as described in Section 8.320, accessory dwelling units are exempt from the requirements of Section 8.320 that:

1. The improvement may not result in the creation of a new story . Accessory dwelling units permitted contingent on an HIE may result in creation of a new story.

2. At least 75 percent of the existing exterior walls (in linear feet) will remain . Accessory dwelling units may be permitted contingent on an HIE regardless of the percent of linear feet of existing walls remaining.

3. At least 50 percent of the existing roof (in sq. ft.) will remain . Accessory dwelling units may be permitted contingent on an HIE regardless of the percent of existing roof remaining.

4. The addition will be located at least three feet from a property line . In the case of accessory dwelling units located within an existing structure, as described in 8.396.050(4), accessory dwelling units may be permitted contingent on an HIE regardless of setbacks.

San Mateo County, California, Code of Ordinances Title 8 – Zoning & Development Code

5. The existing structure is located in an area with an average slope of less than 20 percent . Accessory dwelling units may be permitted contingent on an HIE regardless of the average slope.

These exceptions to HIE standards are applicable only to the accessory dwelling unit, not to the primary residence or any other development on the subject parcel.

Home Improvement Exceptions may not be used to allow an accessory dwelling unit of greater floor area than that allowed by Section 8.396.050(5).

These regulations shall only be applicable in areas inside San Mateo County’s Coastal Zone.

With the exception of specific standards and exemptions described in this Chapter, all accessory dwelling units must comply with all applicable provisions in the San Mateo County Ordinance Code, including the Zoning Regulations (Title 8 et seq.) and the Building Regulations (Title 10 et seq.).

In the Coastal Development (CD) District, all accessory dwelling units shall comply with all of the applicable regulations of the district, including but not limited to the Sensitive Habitats, Visual Resources, and Hazards policies of the Local Coastal Program. Nothing in this Chapter shall be construed to supersede or in any way alter or lessen the effect or application of the California Coastal Act, the San Mateo County Local Coastal Program, or the CD District regulations, except that no public hearing shall be required for accessory dwelling units that meet all relevant standards of this Chapter, and approval of such accessory dwelling unit applications shall be made ministerially, at the staff level. Accessory dwelling units shall count toward the total residential development limits described in Section 1.23 and 3.22 of the County’s Local Coastal Program.

Applications for accessory dwelling units, except for those requiring a conditional use permit as specified in Section 8.396.110, shall be approved or denied ministerially, on the basis of the objective criteria included in this Chapter and other applicable regulations as defined in Section 8.392.130 Consideration of other permits associated with development of the proposed accessory dwelling unit only, that might otherwise be discretionary, including but not limited to Tree Removal, Coastal Development, Resource Management, and Grading Permits, shall also be ministerial, except as provided in Section 8.396.110. Except for units that are within the Coastal Zone’s Appeals Jurisdiction and/or that require a Coastal Development Permit, no public notice or public hearing shall be required for review and approval or denial of an accessory dwelling unit, unless an applicant requests exceptions to the standards set forth in this Chapter. In the case of units that are within the Coastal Zone’s Appeals Jurisdiction, and/or require a Coastal Development permit, all required public notice will be provided.

San Mateo County, California, Code of Ordinances Title 8 – Zoning & Development Code

Decisions to approve or deny an application for an accessory dwelling unit that meets all relevant standards set forth in this Chapter shall not be subject to appeal, except if located in the Coastal Commission appeals area of the CD District, in which case the decision may be appealable as provided in the CD District Regulations, Section 8.252.040(s).

With the exception of specific standards and exemptions described in this Chapter, all accessory dwelling units must comply with all applicable provisions in the San Mateo County Ordinance Code, including the Zoning Regulations (Title 8 et seq.) and the Building Code (Title 10 et seq.).

(Chapter 22.5.1 - Added by Ordinance No. 4834 – September 15, 2020)

(Sections 6439.1 – 6439.18 repealed and replaced in their entirety by Ordinance No. 4851 - September 14, 2021)