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Hillside Protection Overlay District

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The most recent update to the Brentwood comprehensive plan (Brentwood 2020 Plan) identified hillside protection as one of the principal objectives of both our citizens and the City leadership. In result, the Planning Section completed a major work plan assignment in 2008 that resulted in the official adoption of a new hillside protection overlay zoning district (Municipal Code Section 78-341), providing effective guidance for future hillside development in Brentwood. This initiative was preceded by detailed land development revisions affecting lot development standards which address specific site problems associated with hillside lot development.

The new HP Hillside Protection Overlay protects both the scenic vistas and the natural terrain within the City along the higher ridges of the City through specific development standards. These new regulations minimize the impact of building construction and land disturbance activities in steep hillside areas, addressing unsafe geologic disturbance, soil erosion and surface water runoff, excessive removal of trees and other vegetative cover, as well as severe cutting, physical scarring and visual modification of the natural terrain. While the standards make it more difficult to undertake hillside development, they do not prohibit such development entirely as long as such activity is carried out within the guidelines in the ordinance.

The “Hillside Protection (HP) Overlay District” operates in a similar manner to the current floodway overlay district by covering properties within a designated area regardless of the primary zoning district classification for the property. As with the floodway overlay district, the requirements associated with the hillside overlay district shall be in addition to the requirements of the primary zoning district. Unless situated in gently sloping terrain, the hillside overlay district affects most properties located at and above the 850-foot elevation within the City of Brentwood. These properties are clearly the most scenic, visible hillside locations in the City.

Please note that the HP standards only apply to the creation of new lots, construction of new dwellings or buildings, substantial expansion to an existing dwelling (more than 50% or 2,000 square feet, whichever is less), and land disturbance activity affecting more than 10,000 square feetreturn to top

rolling hills and pasture in fall season

Technical/Design Standards

Site Development Standards – The hillside protection overlay district reduces the density of residential development in such areas, setting a minimum lot area of three (3) acres. Within such hillside lots, the maximum allowable area of land disturbance is set at one (1) acre for the first three (3) acres, and one-fifth (1/5) acre for each additional one acre of the tract.  No building structure can be placed in an area of steep grades (over 25 percent grade), thereby limiting development to the flatter areas with conventional or transitional grades (under 25 percent grade). In addition, structures must be placed a minimum of fifty (50) feet away from any steep grades that are visible from the lower elevations (typically the steep areas in front of a structure that is placed on flatter terrain at the top of the hill).

Streets/Driveway Standards - Public or private streets built to City standards in the hillside protection overlay district shall not exceed the maximum permitted grades in the subdivision regulations. Roadway design guidelines for the hillside protection overlay district prohibit retaining walls in excess of ten (10) feet in height as measured from final grade, and no cut and fill sections in the natural topography in excess of twenty (20) feet shall be permitted.

Private driveways shall meet the various construction and grade standards in place (20% maximum grade for hard surfaces and 10% for gravel).  Retaining walls associated with driveway design are limited to six (6) feet in height as measured from final grade and must be constructed of durable materials with colors that visually blend into the natural terrain. Multiple retaining walls of terraced design with landscaping incorporated between to screen the walls are permitted under the new code.  The color and composition of driveway surfaces must also visually blend into the site topography. Maximum allowable cut and fill sections for any driveway shall be 12 feet.

Note that the ordinance limits land disturbance in association with driveway construction to 20 percent of the visible steep grade area located between other properties and roadways at lower elevations and the hillside structure served by the driveway. Upon completion of a driveway, any disturbed slopes must be reestablished and replanted according to a plan approved by the Planning Commission.

Geotechnical Studies – In areas of potential soil instability, the engineering department shall require a formal geotechnical study to address site conditions and recommend appropriate design and construction methods. This ordinance language is broad enough to allow the engineering department to require a geotechnical study in any location with soil concerns.

Architectural and Landscape Standards - To the greatest extent feasible and practical, new structures shall be designed and constructed to blend into the natural terrain, and existing natural vegetation shall be preserved to the greatest extent possible.  Lower profile homes are encouraged that do not extend the roof line of the dwelling above the natural tree line.  Structures should be built of materials and colors that blend into the natural tree line. In addition, due to the relatively remote locations and difficulty in providing traditional fire protection, all new hillside structures intended for occupancy shall be protected by an automatic sprinkler system. In locations with open visibility to surrounding properties at lower elevations, additional evergreen trees and shrubs may be required to screen the structure better.

To facilitate related landscape planning, a tree survey shall be produced for the proposed construction, identifying trees proposed for removal. This tree survey covers the proposed areas of disturbance, and extending fifty feet beyond the proposed areas of disturbance. A plan detailing additional landscape alterations and installations must be produced for Planning Commission review and approval. Note that the ordinance does allow limited removal of vegetation to open limited views from a hillside structure to the areas below, provided 75% of the structure is not visible from lower elevations during the winter season.  return to top

Non-Conforming Lots, Uses & Structures

Any existing lot of record and/or existing structure in the overlay district that was lawfully established prior to adoption of these regulations holds certain rights for continued use and development. However, when there are proposed improvements to expand the existing enclosed area by more than 50% or 2,000 square feet of finishable floor space, whichever is less, the site shall be brought into conformance with the new technical/design standards to the greatest extent feasible. Exceptions to the standards may be approved by the Planning Commission when it determines the proposed plan will better achieve the intent of the overlay district, or when compliance will pose an undue burden on the property owner.  return to top

Planning Commission Approval

As with proposed improvements within the Floodway Overlay District, the regulations for the HP Overlay district require review and approval of hillside development plans by the Planning Commission. Required plan details are similar to site plans presented for development in the commercial and service-institution zoning districts and include site grading, architectural elevations, landscaping, etc. In addition, computer generated graphics with a visual simulation of the proposed structure as it will appear on a photo of the hillside from the various locations, properties and roadways at lower elevations will be required.  return to top