Hillsborough Municipal Code Ch. 16.12 Hillside Lot Size

The intent of this chapter is to regulate land in hillside areas with an average slope of ten percent or greater in order to accomplish one or more of the following:

A. To substantially maintain essential natural features, vegetation, open space, and scenic qualities.

B. To minimize water run-off and soil erosion problems incurred in adjustment of the terrain in order to meet on-site and off-site development needs.

C. To achieve land use densities that are in keeping with the general plan.

D. To insure that the town does not incur an extraordinary or substantial increase in the cost of providing or maintaining public services.

E. To encourage the use of development techniques and alternatives that will be compatible with the terrain, including, but not limited to, implementation of green infrastructure measures identified in the green infrastructure plan approved by resolution of the city council.

(Ord. No. 696, 7-11-2011; Ord. No. 757, § 12, 10-14-2019)

A. "Hillside land" means land having an average percent of slope equal to or exceeding ten percent, calculated pursuant to Section 16.12.040.

B. "Contour interval" means the difference in elevation between adjacent contour lines on a topographical map.

(Ord. No. 696, 7-11-2011)

Notwithstanding any other provision of this code regarding minimum lot size, each lot on hillside land shall be no smaller than the minimum lot size determined pursuant to this chapter.

(Ord. No. 696, 7-11-2011)

A. For purposes of this title, the average percent of slope of a parcel being subdivided, or of a single lot, shall be determined by the formula:

S = 100 IL/A

where

S = Average percent of slope,

I = Contour interval in feet

L = Summation of existing contour length in feet

A = Area of lot (in square feet)

B. The application of this formula is as follows:

[Figure]

EXAMPLE TOPOGRAPHIC MAP

Percent Slope - Sample Calculations

Contour Interval (I) = 5' (from the topographic map above)

Summation Length of Contours (L) (calculated in feet and measured from the topographic map above) = 7,624 feet

Area (A) = 5 acres @ 43,560 sq. ft. = 217,800 sq. ft.

Slope = 100 IL/A = 100 (5) 7,624/217,800 = 17.5%

C. A topographic map showing contours shall be prepared by a licensed land surveyor or civil engineer licensed to practice surveying in State of California. The map shall indicate two foot vertical intervals at a minimum and shall be of a size adequate to allow the calculations required by this chapter to be done.

(Ord. No. 696, 7-11-2011)

A. For proposed subdivisions of hillside land, the calculation of the number and size of lots shall be done in two steps: First, using the slope formula set forth in Section 16.12.040, calculate the average slope percent for the whole parcel proposed to be subdivided. Second, compare this calculated average slope percent to Column 1 of the Slope-Density Table below and determine the maximum number of lots per acre (Column 2 of the Slope-Density Table) and the minimum lot size for the subdivision (Column 3 of the Slope-Density Table). If the average slope percent falls between the numbers shown in Column 1, the numbers for all three columns shall be interpolated. For example, if the average slope percent in Column 1 is 17.5%, the density in Column 2 is 1.70 and the minimum lot size in Column 3 is .59.

Slope-Density Table

B. The maximum number of lots allowed for any proposed subdivision shall be calculated by multiplying the subdivision's total acreage by the density allowed by Column 2. If the resulting number of lots permitted is not a whole number, the number of lots permitted shall be rounded up to the next higher whole number if each resulting lot can individually satisfy the minimum lot size set forth in Column 3; otherwise, the number of lots permitted shall be rounded down to the next lower whole number. In other words, in all cases, the lot size for each lot in the proposed subdivision shall be no smaller than the minimum lot size allowed by Column 3.

C. The calculations required by this section are illustrated as follows:

Sample Lot Calculation

Assume a 5 acre parcel with 17.5% average slope.

This means that:

Column 1 = 17.5

Column 2 = 1.70 (interpolated)

Column 3 = 0.59 (interpolated)

This means that:

1.70 = density per acre of the proposed 5 acre subdivision

1.70 density × 5 acres = 8.5 lots maximum

8.5 lots rounds up to 9 lots

However, each individual lot must meet the requirements of Column 3, i.e., must be at least .59 acres in size. Nine lots at the minimum lot size (9 lots @ .59 acres = 5.31 acres total) exceed the size of the 5 acre site, so only 8 lots maximum (8 lots @ .59 acres = 4.72 acres total) may be allowed in the proposed subdivision.

D. Frontage and other requirements of this and other titles may also affect the maximum number of lots possible in a proposed subdivision and may increase the minimum lot size otherwise applicable to lots on hillside land. Nothing in this chapter shall be deemed to make such other requirements inapplicable.

(Ord. No. 696, 7-11-2011)