Chapter 17.33 — RESIDENTIAL DISTRICT R-1B

Sections:

• 17.33.010 Purpose.

• 17.33.020 Characteristics of the District.

• 17.33.030 Allowed Uses and Permit Requirements.

• 17.33.040 Development Standards.

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

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This chapter identifies the allowed use and permit requirements and development standards for the residential district R-1B. The intent of this district is to implement the residential land use categories of the town’s general 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-1B 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 17.33.030-1 (Allowed Uses and Permit Requirements for Residential District R-1B) identifies the allowed uses in the R-1B 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

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

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Table 17.33.030-1. Allowed Uses and Permit Requirements for Residential District R-1B

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----- Start of picture text -----
Zoning District
Land Use
R-1B
Home occupations P
Mobile and P
manufactured housing [5 ]
Second dwelling unit [2 ] P
Single-room occupancy P
Churches and places of CUP
worship
Public utilities or CUP
facilities
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Notes:

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

2 Subject to compliance with section 17.33.040 (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 Mobile homes and manufactured housing shall be constructed on a permanent foundation.

(Ord. 669 § 4, 2024; Ord. 591 § 10, 2010; Ord. 582 § 1 (Exh. A), 2009)

The following minimum and maximum requirements shall apply in the R-1B 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.

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

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1. Main buildings: twenty-eight feet; provided, that neither vertical side walls or columns exceed eighteen feet. End walls shall be perpendicular to the lot depth.

2. Accessory structures: see chapter 17.40.

3. Detached garages: see chapter 17.40.

4. Consistent with the sidewall height limit for the R-1B 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 17.33.040-1a (Dormers) and 17.33.040-1b (Excessive Dormers)).

Figure 17.33.040-1a. Dormers

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• 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 17.33.040-1b (Excessive Dormers)).

Figure 17.33.040-1b. 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 17.33.040-2 (Dormer Height and Placement)).

Figure 17.33.040-2. 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-1B 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 × 0.165) + 1,500 square feet.

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 17.33.040-3 (Substantially Open Roof)), with the provisions of subsections (C)(2)(a) and (b) of this section.

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

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2. 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), with the provisions of subsections (C)(2)(a) and (b) of this section.

   • 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 17.33.040-3. 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. 

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

  1. Main buildings, interior and corner lots: thirty feet minimum; provided, however, on lots of record prior to adoption of Ordinance No. 277 (October 30, 1967) with a depth less than one hundred sixty feet, the front and rear yards shall each be eighteen percent of the lot depth with a minimum of twenty feet; and

  2. Accessory structures, as provided in chapter 17.40.

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

• E. Side Yards. Minimum side yard requirements are as shown in Table 17.38.010.

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

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

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F. 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.

• G. 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. (Ord. 591 §§ 4—6, 2010; Ord. 582 § 1 (Exh. A), 2009)