Chapter 17.40

ACCESSORY BUILDINGS AND STRUCTURES

Sections:

• 17.40.010 Purpose. 17.40.020 Definitions.

• 17.40.030 Permit Requirements and Exceptions.

• 17.40.040 General Development Standards. 17.40.050 Development Standards for Specific Types of Accessory Buildings and Structures.

The Atherton Municipal Code is current through Ordinance 677, passed February 18, 2026.

Page 106 of 192

Title 17 Zoning | Atherton Municipal Code

The purpose of this chapter is to permit the construction or exterior alterations of accessory buildings and structures subject to regulations necessary to prevent unreasonable interference with views, light, and air, an unreasonable invasion of privacy, or adverse impacts upon the aesthetic character of neighboring residential structures. This chapter establishes a set of criteria, objectives, and procedures to be followed with respect to the review of any proposed accessory structure, or addition or alteration thereto, and to assure that the new development occurs in a manner that is consistent with the objectives of this chapter. (Ord. 582 § 1 (Exh. A), 2009)

Terms that are relevant to this chapter are defined in chapter 17.60 (Definitions). (Ord. 582 § 1 (Exh. A), 2009)

Unless otherwise provided below, all accessory buildings and structures shall require zoning clearance at the time of building permit review or prior to development/installation to ensure compliance with the applicable regulations of this chapter.

A. Special Structure Permit Required. The following specific structures shall require the issuance of a special structure permit from the designated approval authority (planning commission as described in Table 17.06.070-1) prior to development/installation:

1. Athletic courts that are located outside the required setback area (see section 17.40.050(A)).

2. All inflatable covers (see section 17.40.050(G)).

3. Roof-mounted antenna taller than the height limit of the structure to which it is attached. The antenna must be capable of being retracted to a height less than that allowed for the type of building on which it is mounted when it is not in use.

4. Satellite dishes larger than one meter in any dimension, either ground- or building-mounted. Note, the designated approval authority (planning commission as described in Table 17.06.070-1) shall not have the discretion to deny such permit, but shall review each application for conformity to the requirements of this chapter.

5. Arbors and trellises larger than specified in section 17.40.050(B) (Development Standards for Specific Types of Accessory Structures).

6. A pool or spa, exclusive of equipment, when located outside of the area generally allowed, described in section 17.40.040 (General Development Standards) and figure 17.40.040-1 (General Setback Standards for Accessory Buildings and Structures for Interior Lots). See also section 17.40.050(E).

The Atherton Municipal Code is current through Ordinance 677, passed February 18, 2026.

Page 107 of 192

Title 17 Zoning | Atherton Municipal Code

B. Exempt Accessory Buildings and Structures. No zoning clearance or special structure permit is required for the following buildings and structures.

1. Accessory buildings with a floor area that is less than one hundred twenty square feet in size with no portion of the structure more than eight feet in height with the following conditions:

   • a. Structures shall not be located in a required front yard except as otherwise provided.

   • b. In order to maintain necessary fire breaks, accessory buildings shall be set back a minimum of ten feet from side and rear property lines with a minimum eight-foot separation from the main building.

2. Bridges and walkways over private ponds, creeks, and other features, when located on private property.

3. Mailboxes, flagpoles, outside lighting on poles not over three feet tall, and benches to be used for seating.

4. Driveways, walkways, patios, and other flat wood, concrete, or asphalt work or other similar materials not over six inches above grade.

5. A well, located less than six inches above grade, exclusive of tanks, controls, separator discharge plumbing, or other equipment located outside of the well casing, may be constructed in required side or front yards. In no event shall a well be closer than ten feet to any property line.

6. Seat walls not over twenty-four inches in height.

7. Antennas maintained by the town in connection with public safety activities.

8. Satellite dishes measuring not more than one meter in any dimension when attached to a building or placed on the ground and located within the buildable area for a main building or accessory building or structure.

9. Arbors and trellises, consistent with the standards of section 17.40.050(B).

10. Driveways that also function as basketball courts.

11. Bird baths or pedestals with a shallow basin filled with water for birds to bathe in and drink from.

12. Air conditioners and emergency generators located within the buildable area of the lot and enclosed or otherwise screened to mitigate noise and comply with the town noise ordinance. The location of the equipment shall not impact existing trees. Equipment may be located next to existing buildings consistent with building code requirements. Equipment may be located underground when the size is limited to the minimum area needed for the equipment and access and working space, but may not exceed six inches above grade.

13. Fountains and artwork not over six feet in height.

The Atherton Municipal Code is current through Ordinance 677, passed February 18, 2026.

Page 108 of 192

Title 17 Zoning | Atherton Municipal Code

14. Solar facilities are exempt from the minimum ten-foot side yard setback requirement unless the building official has determined that the placement therein will have a specific, adverse impact upon the public health or safety, as defined in State law. (Ord. 609 § 2, 2014; Ord. 582 § 1 (Exh. A), 2009)

The following development standards/provisions apply to all accessory buildings and structures:

A. Location and Required Setbacks. Accessory buildings and structures may be located within required yard areas in compliance with the development standards in Table 17.40.040-1 (General Minimum Setback Standards for Accessory Buildings and Structures). Figure 17.40.040-1 (General Setback Standards for Accessory Buildings and Structures for Interior Lots) illustrates where accessory buildings and structures are generally allowed.

Table 17.40.040-1. General

Minimum Setback Standards for Accessory Buildings and

==> picture [204 x 296] intentionally omitted <==

----- Start of picture text -----
Structures
Location Setback
Front 120 ft., or 30 ft.
behind front line of
main structure,
whichever is less [1, 2 ]
Side, interior 10 ft.
Side, street side See Table 17.38.010
Rear 10 ft.
Rear, abutting 30 ft. [3, 4 ]
street
Between 8 ft. [5, 6 ]
structures and
buildings
----- End of picture text -----

Notes:

1 See special front yard location and setback standards for athletic courts (section 17.40.050(A)), arbors and trellises (section 17.40.050(B)), and artwork and fountains (section 17.40.050(H)).

2 On flag lots, the front setback for accessory buildings and structures shall be consistent with the front yard setback of the main residence upon issuance of a special structure permit.

The Atherton Municipal Code is current through Ordinance 677, passed February 18, 2026.

Page 109 of 192

Title 17 Zoning | Atherton Municipal Code

3 For structures that are less than three feet in height, the minimum setback shall be ten feet.

4 When the rear property line abuts the town boundary, the minimum setback shall be ten feet.

5 Stables shall not be located within forty feet of any building intended or used for human habitation on the same lot, shall not be located within forty feet of any property line, and shall not be located within eighty feet of any building intended or used for human habitation on an adjoining lot.

6 In all cases, the eight-foot separation shall be maintained between the main building and accessory building(s), between the main building and accessory structure(s) and between accessory building(s) and accessory building(s). The separation between accessory building(s) and accessory structure(s) and between accessory structure(s) and accessory structure(s) shall be the minimum distance required under the California Code of Regulations as adopted by the city council.

Figure 17.40.040-1. General Setback Standards for Accessory Buildings and Structures for Interior Lots

The Atherton Municipal Code is current through Ordinance 677, passed February 18, 2026.

Page 110 of 192

Title 17 Zoning | Atherton Municipal Code

==> picture [480 x 549] intentionally omitted <==

B. Height. Unless otherwise specified, the maximum height for all accessory buildings and structures is fifteen feet or one story. Vertical sidewalls or columns shall not exceed eleven feet. No other use of structure shall be located above the first story (i.e., no roof decks, spas, etc.). See chapter 17.42, Building Height and Measurement.

1. Exception for vertical projections. Vertical architectural projections on accessory buildings and structures (e.g., cupolas, spires, towers) may exceed the maximum height by up to two feet, up to a maximum of

The Atherton Municipal Code is current through Ordinance 677, passed February 18, 2026.

Page 111 of 192

Title 17 Zoning | Atherton Municipal Code

seventeen feet; provided, that the footprint of the projection is not more than ten percent of the total footprint of the building. Such projections shall be a minimum of twenty feet from rear and side property lines.

C. Lot Requirements. Unless otherwise identified for specific types of structures or buildings, all accessory buildings and structures shall be constructed only in conjunction with or subsequent to the construction of a main building. An accessory structure or building may be located on a lot without a main building only if all of the following conditions exist:

1. The lot containing the accessory buildings or structure is located adjacent to a lot containing a main building;

2. Both such lots are owned by the same property owner; and

3. An agreement between the town and the property owner has been executed and recorded that provides that in the event common ownership of the two lots ceases then the accessory building or structure will be removed or made to conform to all other provisions of this title.

• D. Kitchens. One kitchen may be within an approved accessory building or structure.

• E. Bathrooms. There shall be no limitation on the number of bathrooms allowed in an accessory building.

• F. Connecting Accessory Buildings and Structures. Accessory buildings and structures shall be detached from the main building and other accessory buildings and structures, except that:

1. An accessory building or structure may be connected to another accessory structure/building or a main building by way of a breezeway or covered walkway when the walkway is open on all sides except where connected to the structures. Examples include, but are not limited to, covered walkways connecting the primary dwelling to a detached garage or secondary dwelling. Structures must be located a minimum of eight feet from the main building. The covered walkway may have a maximum width of eight feet and the length of the walk must be a minimum of two feet longer than the width.

2. A garage shall be considered a part of the main building when it is attached and made an integral part of the dwelling and has at least one common wall of least seven feet in length.

G. Floor Area Ratio Calculation. Accessory buildings and structures shall count towards the allowed floor area ratio of the underlying zoning district as identified in section 17.32.040 (Development Standards for Residential District R-1A) and section 17.33.040 (Development Standards for Residential District R-1B), except that floor area ratio shall exclude the following:

1. Roofed areas open on two or more sides not exceeding five percent of the maximum allowed floor area for the lot plus five hundred square feet (e.g., awning, patio cover, covered walk); and

2. Structures, open on all sides, with substantially open roofs (e.g., trellis), that meet the following criteria:

The Atherton Municipal Code is current through Ordinance 677, passed February 18, 2026.

Page 112 of 192

Title 17 Zoning | Atherton Municipal Code

a. No more than one side of the structure is attached to the main building and no more than one side of the structure is enclosed by small structural features (e.g., outdoor kitchens/barbeques, fire pits/ fireplaces, cabinets); provided, that on the side with the structural feature at least fifty percent of the side is still open (see figure 17.40.040-2 (Attached Trellis Exempt from Floor Area Requirement)); or

b. No more than two sides shall be partially enclosed with small structural features (e.g., outdoor kitchens/barbeques, fire pits/ fireplaces, cabinets); provided, that at least fifty percent of both sides is still open and the other two sides are completely open.

Figure 17.40.040-2. Attached Trellis Exempt from Floor Area Requirement

==> picture [462 x 293] intentionally omitted <==

H. Windows. Accessory buildings and structures may include windows and/or skylights, except that no window or skylight openings that face the side or rear property line shall be located over nine feet above the ground level.

I. Lighting. All lighting on accessory buildings and structures that are located outside of the main building area shall be shielded or downlit and shall not shine onto adjoining properties.

J. Temporary Habitation. Temporary habitation of an accessory building or structure is permitted for a period of no more than thirty days in any calendar year (consecutive or intermittent). Temporary habitation of an accessory building for more than thirty days may be permitted upon issuance of a Conditional Use Permit when the main building is vacant for remodeling or other similar purposes. (Ord. 609 § 1, 2014; Ord. 605 § 1, 2014; Ord. 582 § 1 (Exh. A), 2009)

The Atherton Municipal Code is current through Ordinance 677, passed February 18, 2026.

Page 113 of 192

Title 17 Zoning | Atherton Municipal Code

In addition to the development standards of section 17.40.040 (General Development Standards), the following accessory buildings and structures have special standards and regulations:

A. Athletic Courts. Any athletic court shall be considered an accessory structure and may be located in areas permissible for accessory buildings and structures. Athletic courts may also be located on other portions of the lot, where accessory buildings and structures are normally prohibited, only upon issuance of a special structure permit; however, in no event shall an athletic court be closer to any side or rear property line than specified in Table 17.40.040-1 or closer to the front property line than the minimum front yard setback line of the main dwelling. These types of facilities are intended and are to be used solely for the enjoyment of the occupants and guests of the principal use of the property on which it is located. No commercial or advertised use of the skateboard ramp/BMX tracks shall be permitted and no donations or contributions shall be solicited or received for use of or attendance at skateboard ramp/BMX track activities. Any athletic court shall be constructed or erected in accordance with the following standards:

1. No enclosure or partial enclosure for an athletic court shall be permitted within ten feet of any side or rear property line or closer to the front property line than the front setback line.

2. No enclosure or partial enclosure of an athletic court shall be permitted to exceed nine feet in height from finished grade with the exception of a basketball backboard which is a part of the enclosure.

3. Nets (with the exception of basketball goal nets) which exceed nine feet in height from finished grade shall be removed or lowered to less than nine feet in height when not in use.

4. A structure which is used as a practice board or court wall shall be constructed of a minimum six-inchthick masonry material unless located a minimum sixty feet from any property line.

5. No artificial lighting shall be constructed to illuminate an athletic court.

6. No lighting system or light elsewhere on the property (e.g., landscape lighting, porch lighting) shall be used to illuminate an athletic court.

7. Skateboard Ramps/BMX Tracks. The ramp/track shall be of such a scale and design and constructed of materials which will minimize noise, vibration, and other nuisance factors commonly associated with usage. Portions of the ramp/track may be located below ground level, but in no case shall any portion of the ramp/ track exceed three feet in height above average natural grade, excluding handrails. The ramp shall comply with all pertinent sections of the Uniform Building Code and all zoning requirements of accessory structures. No motorized vehicles shall be allowed in conjunction with the track or ramp. Grading and drainage review is required.

elow ground level, but in no case shall any portion of the ramp/ track exceed three feet in height above average natural grade, excluding handrails. The ramp shall comply with all pertinent sections of the Uniform Building Code and all zoning requirements of accessory structures. No motorized vehicles shall be allowed in conjunction with the track or ramp. Grading and drainage review is required.

8. Batting Cages. No enclosure or partial enclosure of a batting cage shall be permitted to exceed nine feet in height from average natural grade. Netting and sound baffling material shall be used on the enclosure to

The Atherton Municipal Code is current through Ordinance 677, passed February 18, 2026.

Page 114 of 192

Title 17 Zoning | Atherton Municipal Code

absorb the sound. No chain link fencing or other materials that generate sound shall be utilized. If the batting cage is enclosed with walls and a roof, it shall be considered an accessory building and count towards floor area.

• B. Arbors and Trellises. Arbors, trellises, and pergolas are subject to the same development standards as other accessory structures listed in section 17.40.040 (General Development Standards). This includes adhering to the minimum setback standards and the maximum structure height of fifteen feet and maximum sidewall height of eleven feet (e.g., columns and posts are allowed to a maximum of eleven feet and pitched roofs are allowed to a maximum of fifteen feet). However, arbors, trellises, pergolas, and other such structures may be constructed without regard to the setback requirements if conforming to all of the following:

  1. One or more such structures may be built in front of the required accessory structure front setback; provided, that such structures shall not exceed twelve feet in height, eight feet in width, nor a total for all such structures of eight feet in length (see figure 17.40.050-1, Setback Standards for Arbors and Trellises for Interior Lots);

  2. Is not located closer than ten feet to any property line other than a public right-of-way (see figure 17.40.050-1, Setback Standards for Arbors and Trellises for Interior Lots);

  3. Is substantially open to the passage of light and air in all aspects;

  4. Is located outside of the clear visibility area; and

  5. Is expressly for the purpose of and used for supporting vines, roses, or other vegetation (except trees and/or tree limbs).

  6. Lighting shall be shielded or downlit so the source of the light is not visible from other properties.

Figure 17.40.050-1. Setback Standards for Arbors and Trellises for Interior Lots

The Atherton Municipal Code is current through Ordinance 677, passed February 18, 2026.

Page 115 of 192

Title 17 Zoning | Atherton Municipal Code

==> picture [481 x 539] intentionally omitted <==

• C. Roof-Mounted Antennas. Roof-mounted antennas are only permitted when the boom and any active elements of the antenna array are not more than fifteen feet in length and meet the following conditions:

1. That the antenna be attached to a structure that conforms to this zoning code or to a conforming portion of a nonconforming structure.

The Atherton Municipal Code is current through Ordinance 677, passed February 18, 2026.

Page 116 of 192

Title 17 Zoning | Atherton Municipal Code

2. That it be located so it is shielded insofar as practicable by the structure or landscaping from the view of adjacent property and any public street, park, facility, or right-of-way.

3. That it not exceed the height limit applicable to the structure to which it is attached, with the exception that if a special structures permit is granted so providing, an antenna with the capability of being retracted to a height less than that allowed for the type of building on which it is mounted may exceed the height limit during the actual use for transmitting and receiving.

4. Each antenna shall be constructed of low-visibility materials and shall be finished with a low-visibility, nonglare paint or other finish, consistent with its location and surroundings.

5. Roof-mounted amateur radio antennas provide an essential telecommunication service during periods of disaster and other emergency conditions and are therefore exempt from the provisions of this chapter when in compliance with the following standards:

   • a. The antenna is forty-five feet or less in height as measured from the ground to the highest point of the antenna, unless the tower is equipped with a lowering device (motorized or mechanical) capable of lowering the antenna to the maximum permitted height when not in operation, in which case the antenna must be not more than seventy-five feet in height.

   • b. The operator registers their amateur radio antenna, including type of antenna (e.g., fixed or retractable) and height, with the town.

   • c. Consistent with federal law, additional height may be permitted through issuance of a special structures permit, provided the approval authority makes a specific finding that the requested height for the amateur radio antenna is needed to enable communication between antennas.

D. Ground-Mounted Antennas. A ground-mounted antenna is only permitted when the following conditions are met:

1. That the antenna be located in the rear yard.

2. That it meets all requirements of this chapter for accessory buildings and structures.

3. That it be screened by fences, buildings, or landscaping from the view of adjacent property and any public street, park, facility, or right-of-way.

4. That it have an antenna height of not more than fifteen feet.

5. Each antenna shall be constructed of low-visibility materials and shall be finished with a low-visibility, nonglare paint or other finish, consistent with its location and surroundings.

6. Ground-mounted amateur radio antennas provide an essential telecommunication service during periods of disaster and other emergency conditions and are therefore exempt from the provisions of this chapter when in compliance with the following standards:

The Atherton Municipal Code is current through Ordinance 677, passed February 18, 2026.

Page 117 of 192

Title 17 Zoning | Atherton Municipal Code

• a. The antenna is not more than forty-five feet in height as measured from the ground to the top of the antenna, unless the tower is equipped with a lowering device (motorized or mechanical) capable of lowering the antenna to the maximum permitted height when not in operation, in which case the antenna must be not more than seventy-five feet in height.

• b. All antenna structures are set back a minimum distance of ten feet from interior property lines.

• c. All antennas are located within an enclosed fenced area or have a minimum five-foot tower shield at the tower base to prevent climbing. All active elements of antennas shall have a minimum vertical clearance of eight feet.

• d. The operator registers their amateur radio antenna, including type of antenna (e.g., fixed or retractable) and height, with the town.

• e. Consistent with federal law, additional height may be permitted through issuance of a special structures permit, provided the approval authority makes a specific finding that the requested height for the amateur radio antenna is needed to enable communication between antennas.

E. Pools and Spas. A pool or spa shall be located within the area generally allowed, identified in Table 17.40.040-1 (General Minimum Setback Standards for Accessory Buildings and Structures) and figure 17.40.040-1 (General Setback Standards for Accessory Buildings and Structures for Interior Lots). However, upon issuance of a special structure permit, a pool or spa may be located up to ten feet from side and rear property lines and between the front yard setback line and the front line of the main structure.

F. Pool Equipment Operation. No pumping, filter, or similar equipment shall be operated between the hours of eight p.m. and eight a.m., and all permits for the erection of pumping, filter, or other similar equipment shall include the installation of an automatic timing device adjusted to ensure such hours of operation.

G. Inflatable Covers.

1. Screening. Inflatable covers shall be screened from public view or view from other properties.

2. Height. No inflatable cover shall exceed nine feet in height as measured from the ground.

3. The designated approval authority (the planning commission as described in Table 17.06.070-1), in approving the special structures permit, may establish time limits on the permit and other conditions as deemed appropriate by the approval authority.

4. Existing inflatable covers in use at the time of adoption of this title shall be existing nonconforming structures and may continue to be used; provided, that they are maintained in the same location and under the same ownership. (Code Effective: November 20, 2009).

H. Artwork and Fountains. Consistent with the setback requirements of Table 17.40.040-1 (General Minimum Setback Standards for Accessory Buildings and Structures), artwork and fountains are permitted in the following lot areas, consistent with specified development standards:

The Atherton Municipal Code is current through Ordinance 677, passed February 18, 2026.

Page 118 of 192

Title 17 Zoning | Atherton Municipal Code

1. Front Yards. Artwork and fountains may be located in required front yard areas provided they are set back twenty feet from the front property line, are no taller than eleven feet in height, and are not more than one hundred twenty square feet in total area (see figure 17.40.050-2 (Setbacks for Artwork and Fountains)).

2. All Other Areas. Artwork may be located in side and rear yard areas provided they are set back from property lines consistent with Table 17.40.040-1 (General Minimum Setback Standards for Accessory Buildings and Structures) and are no taller than eleven feet in height (see figure 17.40.050-2 (Setbacks for Artwork and Fountains)).

Figure 17.40.050-2. Setbacks for Artwork and Fountains

The Atherton Municipal Code is current through Ordinance 677, passed February 18, 2026.

Page 119 of 192

Title 17 Zoning | Atherton Municipal Code

==> picture [481 x 526] intentionally omitted <==

I. Solar facilities other than pumps for water heaters not exceeding six feet in height are exempt from the minimum ten-foot side yard requirement. (Ord. 605 § 3, 2014; Ord. 582 § 1 (Exh. A), 2009)

The Atherton Municipal Code is current through Ordinance 677, passed February 18, 2026.

Page 120 of 192

Title 17 Zoning | Atherton Municipal Code