Chapter 17.42 — BUILDING HEIGHT AND MEASUREMENT

Sections:

• 17.42.010 Purpose.

17.42.020 Building Height. 17.42.030 Height Measurement. 17.42.040 Exceptions to Height Limit for Main Structures.

This chapter describes the required methods for measuring the height of structures in compliance with the height limits and exceptions as established by this zoning code. (Ord. 582 § 1 (Exh. A), 2009)

A. Except as otherwise provided in section 17.42.040 (Exceptions to Height Limit for Main Structures), the height of structures shall not exceed the height limit for the applicable zoning district established by division II.

• B. Additional height provisions for fences and walls are listed in chapter 17.46 (Fences and Walls).

• C. Additional height provisions for accessory buildings and structures are listed in chapter 17.40 (Accessory Buildings and Structures). (Ord. 582 § 1 (Exh. A), 2009)

A. Height Measurement Generally. The allowable height shall be measured as the vertical distance at any point from the average natural grade within the building pad area to the topmost portion of the building or structure including structural framing and roof covering material. Continuous decorative roof elements, including but not limited to widow walks and railings, shall be included in the maximum building height. Height measurement shall not prohibit any portion of the building measuring fifteen feet or less in height as measured from the finished ground surface adjoining the wall (referred to as the height differential). Natural grade shall mean the original condition of the ground surface as it existed prior to mechanical grading or disturbance. Where the original condition of the ground surface cannot be determined, the town planner may approve a topographic survey of the property prepared by a registered civil engineer or licensed land surveyor indicating the approximate original condition of the ground surface of the site as can best be determined from record and survey data. Average natural grade shall mean the average elevation of the natural grade based upon twelve points of measure along the perimeter of the building prior to any cut and fill. Each point of measure shall be located (first) at every corner

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

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of the building and (second) every thirty feet along continuous walls with lengths over fifty feet. A “corner” shall mean a change in the wall plane of thirty degrees or more. However, if a building has more than twelve corners, then each corner shall be a point of measure regardless of the twelve-point requirement. The points shall be determined by starting at the most northerly corner of the building or structure as determined by magnetic north then moving clockwise around the building or structure. The calculation of the average shall be based on the following formula:

Elevation of point A + Elevation of point B…÷ the number of points = Average Natural Grade

See figure 17.42.030-1 (Elevation Points on a Parcel) for a representation of the elevation points located on a parcel and figure 17.42.030-2 (Height Measurements for Primary Structures).

Figure 17.42.030-1. Elevation Points on a Parcel

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Figure 17.42.030-2. Height Measurements for Primary Structures

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

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1. The building permit set of plans shall include the calculations determining the average natural grade for the property, including the locations and elevations of the natural grade elevation points around the perimeter of the building footprint.

2. Certification by the applicant’s civil engineer (or licensed land surveyor) that the existing conditions topographic map accompanying the building permit set of plans shows natural grade as defined in this section.

3. A certification by the applicant’s civil engineer (or licensed land surveyor) that, at the time of the roof framing inspection, the height of the building does not exceed the allowable height as specified in this title. That certification shall be accompanied by survey notes or other similar data to permit verification of the calculations by a third party. Additionally, a “non-removable benchmark elevation marker” shall be placed on the site and noted on all plans submitted.

4. Upon submission of a civil engineer’s report that finds a substantial portion of the buildable area of a lot is subject to inundation, the building pad can be raised up to one foot above the engineered flood level. The height of any building or structure placed on this raised pad shall be calculated from the new pad grade, rather than the previous existing grade. The addition of fill to the site shall not negatively impact the potential allowed height of any building or structure.

B. Height Measurements for Basements. When a building includes a basement, as defined in this title, the height of the building shall be measured as described in subsection (A) of this section. Where a home with a basement includes a lightwell, stairwell, driveway access, or other excavated feature, the height shall be measured from that point on the building where the natural grade would be if the lightwell or other excavated feature were not developed. See figure 17.42.030-3 (Height Measurement for Basements).

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

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Figure 17.42.030-3. Height Measurement for Basements

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C. Height Measurement for Sidewalls. The height of sidewalls shall be measured from the average natural grade to the base of the roof plate directly above. (Ord. 582 § 1 (Exh. A), 2009)

Exceptions to height limits on main structures include:

A. Chimneys located on the main residential structure, provided they do not exceed six feet in height above the roofline of the structure.

B. Solar panels may extend above the height limit for the zoning district subject to standards and regulations that ensure that the panels will not have a specific, adverse impact upon the public health or safety, as defined by State law.

C. On main buildings, architectural projections (e.g. towers, cupolas) individually totaling no more than four hundred square feet in footprint area are allowed to extend from the main building to a maximum of twenty-eight feet to the sidewall and thirty feet to the roof top. See figure 14.42.040-1 (Allowed Tower/Stairwell Height).

Figure 17.42.040-1. Allowed Tower/Stairwell Height

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

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D. Exception for Vertical Projections. Vertical architectural projections on accessory buildings and structures (e.g., cupolas, spires, towers) may exceed the maximum height by two feet, up to a maximum of seventeen feet; provided, that the footprint of the projection is not more than five percent of the total footprint of the building. (Ord. 582 § 1 (Exh. A), 2009)