Chapter 17.32

RESIDENTIAL DISTRICT R-1A

Sections:

• 17.32.010 Purpose.

• 17.32.020 Characteristics of the District.

• 17.32.030 Allowed Uses and Permit Requirements.

• 17.32.040 Development Standards.

This chapter identifies the allowed use and permit requirements and development standards for the residential district R-1A. The intent of this district is to implement the residential land use categories of the town’s general

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

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plan. It is designed to designate land for the development of residential uses consistent with the development regulations set forth in this title. (Ord. 582 § 1 (Exh. A), 2009)

Residential district R-1A provides for the development of single-family residential uses at a density of one dwelling unit per lot. It allows for new subdivisions with a minimum lot size of one acre. Second dwelling units are permitted, consistent with the development standards of this title. Home occupations are also appropriate for this district, consistent with the development standards of this title. Other uses, including churches and public utilities and facilities, may be allowed upon issuance of a conditional use permit. (Ord. 582 § 1 (Exh. A), 2009)

Table 17.32.030-1 (Allowed Uses and Permit Requirements for Residential District R-1A) identifies the allowed uses in the R-1A zoning district subject to the development standards of this chapter and all other provisions of this title. Allowed use provisions are symbolized in the table as follows:

P = Land use permitted by right

CUP = Land use permitted with approval of a conditional use permit

Table 17.32.030-1. Allowed Uses

and Permit Requirements for

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Residential District R-1A
Zoning District
Land Use
R-1A
Single-family dwelling [1,3 ] P
Employee housing [4 ] P
Group homes for P
persons with disabilities
Home occupations P
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The Atherton Municipal Code is current through Ordinance 677, passed February 18, 2026.

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Table 17.32.030-1. Allowed Uses

and Permit Requirements for Residential District R-1A

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Zoning District
Land Use
R-1A
Mobile and P
manufactured housing [8 ]
Multifamily P
residential [5,6,7 ]
Second dwelling unit [2 ] P
Single-room occupancy P
Churches and places of CUP
worship
Public utilities or facilities CUP
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Notes:

1 Includes associated accessory uses, accessory buildings, and accessory structures (Note: Garages are accessory buildings).

2 Subject to compliance with section 17.32.040 (Development Standards) and chapter 17.52 (Accessory Dwelling Units).

3 Includes residential care facility (defined as a facility serving six or fewer persons).

4 Agricultural employee housing for six or fewer employees shall be treated as a single-family structure pursuant to California Health and Safety Code Section 17021.5.

5 Shall only be permitted on lots with a Multifamily Overlay District (RM-10) designation. Subject to compliance with objective design standards in chapter 17.35 (Multifamily Overlay District RM-10).

6 Pursuant to Government Code Section 65651, a one hundred percent affordable housing development that provides twenty-five percent of its total units, or twelve units, as permanent supportive housing, is principally permitted within the multifamily overlay.

7 Pursuant to Government Code Section 65660, a low-barrier navigation center is principally permitted on any parcel within the multifamily overlay.

8 Mobile homes and manufactured housing shall be constructed on a permanent foundation.

(Ord. 669 § 4, 2024; Ord. 591 § 9, 2010; Ord. 582 § 1 (Exh. A), 2009)

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

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The following minimum and maximum requirements shall apply in the R-1A district. The town planner will review development applications against these standards to determine compliance with applicable zoning regulations.

• A. Height. The maximum building heights permitted are provided below. See also chapter 17.42 for height measurement.

  1. The standard maximum height for main buildings shall be thirty feet; provided, that vertical sidewalls and columns may not exceed twenty-two feet; and provided further, that these standard maximum heights may be increased, but in no event to exceed thirty-four feet for main buildings nor to exceed twenty-eight feet for vertical sidewalls and columns, as follows:

     • a. The main building, vertical sidewalls, and columns height may be increased in any case where the front, rear, and side yards as measured to the area(s) having the increased vertical height, are increased above the standard setbacks by a ratio of at least five feet for each one-foot increase of height; and

     • b. Increased height for a main building (but not to exceed thirty-four feet) or for vertical sidewalls or columns (but not to exceed twenty-eight feet) shall be permitted upon approval of a special structure permit.

  2. Accessory structures: see chapter 17.40.

  3. Detached garages: see chapter 17.40.

4. Consistent with the sidewall height limit for the R-1A zone, dormers that exceed or are otherwise built above the sidewall height limit for the structure, as measured from the extension of the eave line across the width of the dormer, shall be developed consistent with the following standards (see figures 17.32.040-1a (Dormers) and 17.32.040-1b (Excessive Dormers)).

• a. The maximum combined length of all dormers on a side or elevation of a building shall not exceed fifty percent of the total length of the respective side or elevation of the building to which they are associated (see figure 17.32.040-1b (Excessive Dormers)).

Figure 17.32.040-1a. Dormers

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

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Figure 17.32.040-1b. Excessive Dormers

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

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b. The face of the dormer shall be a minimum of two feet below the ridge line (see figure 17.32.040-2 (Dormer Height and Placement)).

Figure 17.32.040-2. Dormer Height and Placement

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

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B. Lot Size Requirements. New lots created in the R-1A district shall be consistent with the lot size requirements established in section 16.24.050 (Lot Size Requirements).

C. Maximum Floor Area Ratio. The maximum floor area ratio shall be eighteen percent of the lot size except for those lots smaller than forty-three thousand five hundred sixty square feet (one acre), which shall be determined by the following equation:

Floor area in square feet = (lot size in square feet × 0.163) + 726 square feet, with a minimum allowable floor area of 2,250 square feet.

The floor area above the first floor of the main building for all lots shall not exceed seven and one-half percent of the lot size.

The following conditions shall not be included in floor area calculations:

1. Structures, open on all sides, with substantially open roofs (e.g., trellis) (see figure 17.32.040-3 (Substantially Open Roof)), with the following provisions:

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

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a. No more than one side of the structure shall be attached to the main building and no more than one side of the structure may be 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

Figure 17.32.040-3. Substantially Open Roof

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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; and

2. Roofed areas completely open on two or more sides up to five percent of the maximum allowed floor area for the lot plus five hundred square feet (e.g., awning, patio cover, covered walk).

• D. Front and Rear Yards. Minimum front and rear yard requirements are:

1. Main building, interior, and corner lots: sixty feet minimum; provided, however, on lots of record prior to adoption of Ordinance No. 146 (April 16, 1946) with a depth of less than two hundred feet, the front and rear yards shall each be thirty percent of the lot depth with a minimum of thirty feet; provided further, where main building heights are between thirty feet and thirty-four feet, the front and rear yards shall be increased by a ratio of five feet for each one-foot increase in height.

2. Accessory structures: as provided in chapter 17.40.

3. The property owned by the City and County of San Francisco, known as the Hetch Hetchy property, over which the owner of adjacent property with contiguous frontage has reserved surface rights, may be utilized by the adjacent property owner for setback calculation purposes. The adjacent property owner may calculate

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

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setbacks to the original property line prior to the acquisition by the City and County of San Francisco, or, in the case of properties subdivided after that date, to the centerline of the Hetch Hetchy property.

4. Second Dwelling Units. As provided in chapter 17.52.

• E. Side Yards. Minimum side yard requirements are as shown in Table 17.38.010; provided, however, where main building heights are between thirty feet and thirty-four feet with the issuance of a special structure permit, the side yards shall be increased by a ratio of five feet for each one-foot increase in height.

  1. The property owned by the City and County of San Francisco, known as the Hetch Hetchy property, over which the owner of adjacent property with contiguous frontage has reserved surface rights, may be utilized by the adjacent property owner for setback calculation purposes. The adjacent property owner may calculate setbacks to the original property line prior to the acquisition by the City and County of San Francisco, or, in the case of properties subdivided after that date, to the centerline of the Hetch Hetchy property.

  2. Second Dwelling Units. Minimum side yard requirements are as provided in chapter 17.52.

F. Accessory Structure Area. Maximum area permitted for all accessory structures, exclusive of pools, tennis courts, garages, carports, drives, and other paved surfaces, on a building site shall not exceed the ratio of one thousand two hundred square feet of accessory structure for each forty-three thousand five hundred sixty square feet of lot area.

G. Eaves. Roof eaves may encroach into any yard not to exceed a maximum of four feet on the main building and not to exceed one foot on an accessory building.

• H. Kitchens.

  1. There is no limitation on the maximum number of kitchens for the main dwelling.

  2. One kitchen may be within an approved second dwelling unit that is located within the main dwelling building setback lines. (Ord. 627 § 1, 2017; Ord. 591 §§ 2, 3, 2010; Ord. 582 § 1 (Exh. A), 2009)