Which subdivision has the steepest slope

Three full living levels, the clients are young and energetic : enter the house on grade on the middle level, a square foot great room with expansive views to the southwest through the treetops.

The lowest level will include a private guest suite, a large art studio, both with on- grade walk-outs , and mechanical and storage rooms. Detach the garage so its elevation can be independent of the house. We schedule an exploratory meeting with the City Engineer and senior members of the zoning and building staffs and the fire chief. We preset our site plan concept, a sketched house plan and house plan, and a 3D massing model.

They pronounce the concept sound with some reservations:. They warn us not to cross an on-site sewer easement with cars. It runs the full width of the site half way between the street and the proposed house location. They express concern over where and how to channel rainfall from the impermeable house and garage roofs and driveway, potentially destabilizing the slope.

And the nearest municipal storm sewer is over feet away uphill from the site. They remind us of the requirement to engage a geo-tech engineer who would take soil borings and advise us and the City on the design of a foundation that would bear on stable soil.

When approved, there will be a buffer of 15 feet around the structures and driveway that may be landscaped, but no alterations of any kind can be made to the remainder of the site. My client had already engaged a geotechnical engineer. Soil borings are taken in several locations at and near our proposed house location. My client and I meet with the engineer to get the results and to strategize on the issues raised by the City.

His report was mixed:. The soil is stable enough to support the foundation without many extra bells and whistles. The design of the house and the proposed siting fit each other nicely, with only a portion of one wall requiring a pour of over 8 feet. The sewer line is near the surface. Making the necessary cuts for a driveway might in fact expose the line.

The only way for cars to access the house will be to replace about 40 feet of the line with a deeper line at a huge cost borne by my clien.

Rainwater from the impermeable roofs and driveway cannot be drained anywhere onto our site. The soil is not stable enough. And the nearest city storm sewer is over feet away, uphill from the house pumping required! A creative and realistic approach. Fortunately, this client wants to satisfy the City by addressing each issue proactively and creatively. Our case for the special permit includes:. Lot Slope Policy is applied on a lot-by-lot basis at the time of preliminary subdivision design.

Each individual lot is sized according to the terrain the lot falls on with the objective of obtaining the best lot design and consequently, in most cases, the best house site for that type of terrain.

Under the Marin County lot slope policy, the minimum size for hillside lots increases as the slope increases. The largest lot required under the zoning ordinance is 9, square feet. The Marin County policy is a policy — not an ordinance provision — carried out in administration of the zoning ordinance, but it might be desirable to make the requirements and chart see Figure 1 part of an ordinance. The result of the Marin County policy is that a hillside development does not have a per lot or per acre density, but does have an average density per acre for the entire development.

The Tiburon Peninsula master plan report says:. The entire hillside area is expected to average approximately two homes to the acre. This over-all density figure does not indicate any particular density for any particular parcel of land: in other words, "lot slope policy," as applied to each individual building site, is the governing device in subdivision design.

In hillside subdivisions in which "lot size averaging" is used instead of conventional minimum lot size, the major problem is on what basis improvements should be required. It is not feasible to require improvements according to lot sizes that vary so much.

That method could result in foot pavement for a half-acre lot and foot pavement for an adjoining one-acre lot, for instance.

Instead, improvements must be required on the basis of anticipated over-all density. But determining the anticipated over-all holding capacity is the difficulty. It cannot be done on a lot-density formula basis, as it can be for flat land subdivisions. Instead, the number of lots in any single hillside development must be determined on the basis of a "lot slope policy" and the holding capacity for the entire subdivision figured from the number of lots. Public facilities and services must be planned accordingly.

Actually estimating the basis for public utilities and services is not as complex as might first appear. Moreover, improvement requirements especially for hillside projects might be included in the subdivision ordinance.

As it is pointed out in the Tiburon Peninsula master plan, the number of lots in a hillside area will be determined to some degree by the layout of the roads. Experience has shown that the use of the lot slope system plus the best possible street layout and the best lot design will usually give the subdivider the maximum number of good building sites. The Marin County approach to densities and lot sizes for hillside subdivisions has much to recommend it. Once the planning agency has a rough idea of the number of families and the number of people an area can accommodate, it can set a minimum lot size.

Many of the lots will be considerably larger than the minimum and some part of the site will be unsuitable for development, but the developer will have a great deal of flexibility in lot sizes and at the same time the planning agency can maintain high development standards.

The real point of control over hillside developments then becomes the subdivision review process. Some planners think hillside subdivisions should be subject to the same subdivision regulations that govern flat land developments of the same density — an approach subject to strong attack by developers, who argue that it is inflexible.

Flat land requirements applied to steep terrain, they say, lead to tremendous earth moving operations, total transformation of the site, and problems of compaction of fill areas.

Hillsides do not lend themselves to the mass production type of residential development for which most subdivision regulations were written. Greater flexibility in subdivision controls has been achieved in some California cities by relating subdivision standards to the lot size provisions of the zoning ordinance. For example, in the Redding, California subdivision ordinance hillside areas are defined and four types of "hillside area" subdivisions are set up.

Apparently the four types are based on lot size requirements for "combining districts," under the zoning ordinance, not on the slope standards in the subdivision ordinance.

The standards under A type I subdivision is one in which the lot size is between 6, and 10, square feet with all of the lots having an area of not less than 6, square feet. In this classification are subdivisions in which all lots have an area in excess of 10, square feet.

In this classification are subdivisions in which 80 per cent of all lots have an area of 20, square feet or over, and the average area of all lots is 20, square feet or over. Eighty per cent of the lots in this classification shall be one acre or over and the average area of all lots in the subdivision shall be one acre or over. The subdivision provisions for lot sizes are presumably based on the zoning ordinance provisions for lot sizes, as they appear in the "combining districts.

The "combining district" provision of the zoning ordinance provides for a "B"-1" lot of 10, square feet. Obviously, the Type II lot is defined so as to fall within the lot size class of the "B"-1" combining district. The "combining district" provision appears below:. All other provisions of the respective districts shall apply.

On any land graded or benched for building sites not more than 10 per cent of area of the lot is to be left in slope steeper than original ground or steeper than 25 per cent, whichever is greater, unless approval is obtained from the Planning Commission prior to obtaining a building permit.

The approach used in Redding is also used in San Mateo, California, where the idea apparently originated with the planning agency, and in San Carlos, California. Adoption of this technique — classification by lot size and varying requirements — should get around the problem that arises if special provisions lowering standards for all kinds of improvements in hillside or other large-lot, low-density subdivisions are written into a subdivision ordinance.

The reduced standards for hillsides, many planners have feared, would become the standards for all subdivisions. Requirements that vary with varying situations is a common device used in zoning ordinances that can be adapted to subdivision regulations with success. The "classification by lot size" approach with varying standards for improvements cannot, however, be combined with a "lot slope policy," since under it lot sizes vary widely within any single subdivision.

Some communities have tried to handle hillside development by permitting variances from the flat land requirements of the subdivision ordinance. If there are no standards for hillside developments to guide the administrator, however, the variance procedure becomes a game of bargaining for concessions between the administrator and the subdivider — a game out of which many abuses can arise.

The subdivider buying land must know what standards he must conform to in order to estimate his development costs accurately. The city administration must be in a position to refer to established standards in order to properly and fairly review the plans submitted for approval. It is apparent, also, that a policy of varying requirements to meet the situation on each particular job is certain to result in time-consuming negotiations and misunderstandings, as well as in an inconsistent and broken street pattern.

In the majority of communities, regulation of hillside development through subdivision controls has taken the form of amendments to the basic ordinance — amendments aimed at particular problems.

Los Angeles County has made a number of studies of hillside development problems, all leading to subdivision ordinance amendments. Some communities have also supplemented such amendments with a grading ordinance since grading and cut-and-fill operations have been the biggest problems and the point at which controls can be of the greatest value.

In communities in which amendments for hillside problems have been adopted, perhaps supplemented by a grading ordinance, the principal point of control has been design review. Without modifications in improvement standards, the average flat land subdivision ordinance can only be adapted for use on hillside areas by careful control of subdivision design.

Another method of putting hillside regulations into effect is by preparation and adoption of a master plan for the entire hillside area. This method has been used by Marin County, for instance, for the Tiburon Peninsula, referred to earlier. It has also been employed by the Tucson-Pima County Planning Commission in the development of the Catalina Foothills, a 5,acre area about a mile north of Tucson.

Under the plan, major rights-of-way are mapped and the property owners grant to the county a deed of easement for the right-of-way. When an acceptable subdivision plat has been recorded, the area described by the plat is zoned from SR suburban ranch to CR-1 single residence.

In addition, the developers impose private restrictions, an unusual feature of which is a prohibition against the destruction or removal of any "native growth" including cacti and Palo Verde trees except that in the way of construction. The intention is to preserve as far as possible the plant life, rock deposits, and wildlife that contribute to the desirability of the area for residential use.

Which of the approaches outlined above is the best? The planning agency working on hillside problems may want to use a little of each. It may want to vary regulations by classes; in unusual situations it may believe that variances are justified. It will certainly want to make amendments to the subdivision ordinance and will often suggest adoption of a grading ordinance. All of the approaches merit consideration.

Streets are the most crucial factor in adjusting flat land design and improvement standards to hillside areas. A whole series of related problems center around them — paving and right-of-way widths, layout, curbs and gutters, sidewalks, vertical and horizontal curves, grades, use of private means of access to lots, on-street and off-street parking, and setbacks. Traffic engineers and planners think that street standards must be related to the kinds and amounts of traffic the streets will carry 3.

The hierarchy of street types — minor street, collector street, arterial street, and expressway — is familiar to all. In hillside areas minor and collector streets are dealt with almost exclusively. The functions of a street in a new hillside subdivision can only be determined and the street classified when it is considered in relation to the entire street pattern of the area; and the differences in function, by types, should be made clear in the street pattern.

Moreover, the pattern should be determined for an area large enough to enable an accurate estimate of the traffic, both for the immediately proposed subdivision and later developments in the area. Obviously, it is not possible to plan a good street pattern for an entire area if only one small piece is considered at a time. The function of the street — its type — is directly related to expected traffic volume.

And traffic volume in turn is related to the traffic pattern and the number of traffic generators along a street. In a residential area, traffic generation can be derived from population density. Once the density factors — lot size and residence type — have been determined, as well as the proposed street pattern, traffic volume is predictable and street types can be designated as needed to serve the area.

The basic physical differences between the street types are in cross-section — width of right-of-way, width of paving based on number and width of moving and parking lanes , median strips, and sidewalks. The tables in the Redding ordinance illustrate how these features can be varied. The major element of concern, however, is the number and width of moving and parking lanes.

Developers of hillside areas have directed most of their protests of "excessive" street improvement standards at the paving widths required for minor and collector streets.

They claim it is possible to eliminate parking lanes from minor and collector streets in hillside areas with savings in paving costs and grading because the narrower the paved area is, the less grading is needed.

Aesthetics is also a reason given by planners and developers for reducing the width of hillside streets. Bestor says: "Wide streets destroy trees and natural land formations and heavy lot grading often eliminates what is left of the natural beauties of the original hillside. Planners are not sure that parking lanes can be eliminated. However, Mr. Bestor advocates an alternative — parking bays.

He makes the point that "As long as one or both sides of a street serve as elongated parking-lots, the pavement cannot be materially narrowed. Bestor notes that in flat land developments driveways can be used for off-street parking, but that in hillside areas many driveways are so short that they cannot. To assure adequate parking spaces, he suggests that an estimate of the over-all parking requirements be made and that "the deed restriction.

To provide for other parking needs, such as the car with the flat tire, he suggests that the developer "provide parking bays outside the flowline of gutter, and these should be suitably surfaced at the time of street construction. But as lot frontage increases, the savings in road building should become evident. A narrow street could wind among the trees and avoid local steep spots, whereas a 35 or 40 foot pavement could only be "blasted through.

Good trees could be left in place within 20 feet of the road centerline and, as mentioned, [the street] could be detoured around an especially fine oak. In breaks between trees, or where cross slopes ease, bays could be introduced on one or both sides of the street. Bestor goes on to say that public officials should not oppose narrower streets and consequent elimination of some on-street parking because of the possibility that emergency vehicles might have trouble when some one has a big party.

The parking bay merits consideration by planning agencies. There may be difficulties in engineering street drainage and providing gutters and curbs but these problems should be solvable. Provision of parking bays may justify narrower than standard streets. Ninety degree parking in bays might be a desirable solution on steep streets, Mr. Bestor suggests. Some planning agencies have adopted special standards for cross-sections of streets in hillside areas.

Sometimes the hillside street is defined as a special class in the definitions section of the subdivision ordinance, as minor, collector, or arterial streets are. In other cases, special hillside streets are allowed in areas considered suitable by the reviewing authority.

The primary purpose of having a hillside street classification is to allow a reduced cross-section — both right-of-way and paving width. For example, the Tulare County, California, subdivision regulations say:. In mountainous areas standards for road right-of-way width and paving width for minor streets and cul-de-sacs may be reduced to forty feet 40' and twenty-six feet 26' respectively. Minor streets in flat areas in Tulare County must have foot rights-of-way and foot paving.

Mountainous areas are defined as those "above 1, feet elevation according to United States Survey datum. In the Santa Barbara, California subdivision ordinance , steep hillside streets are defined as a special class:. Right-of-way and paving widths required for steep hillsides are only slightly less than those required for a minor street, however.

Under the Burbank, California municipal code, the reviewing authority determines in what cases reduced cross-section streets are permissible:. The width of streets on hillside or mountainous land shall be determined by future traffic needs and topographical conditions. All mountainous highways which form a part of primary or secondary traffic routes shall have a minimum [pavement] width of forty 40 feet, but shall be made wider where the topography will permit.

Other mountainous roads of more than frontage importance shall have a minimum width of twenty-six 26 feet. These widths shall be approved only where the City Planning Commission, in the exercise of reasonable discretion, determines that the cross slope will not permit a greater width.

Hillside and mountainous areas are not defined in the Burbank code, so the planning agency presumably grants variances as each case comes up.

As the foregoing examples show, the reduction in standards for hillside streets are often not sufficient to meet the problems of excessive grading and paving.

If the goal is to reduce the amount of land that is scarred in the course of street construction, planning agencies should consider using rights-of-way widths as narrow as 40 feet and paving widths as narrow as 18 to 20 feet. Other subdivision ordinances follow the technique of varying pavement requirements by lot size. The Contra Costa County, California subdivision ordinance , for example, allows a minor street to have a paved width of 20 feet if the lot is more than 40, square feet and the lot frontage is greater than feet.

The Santa Barbara County subdivision ordinance permits a foot paved road in a "rural type" subdivision. A "rural type "subdivision is defined as a "subdivision in which the parcels average at least feet in width and [have] an average lot area of 30, square feet or more, exclusive of roads. There are two classes of subdivisions defined in the Richmond, California, subdivision ordinance The class B subdivision is an area within which 80 per cent of the lots have an area of 20, square feet or more and in which the average size of all lots is 20, square feet or more.

In a class B subdivision, a type III street — paved width of 22 feet, paved valley gutters no curb , and no sidewalks — is permitted. Drafters of the Fremont, California subdivision ordinance saw the need for special provisions for hillside subdivisions:. In the case of subdivisions or portions thereof having an average slope of not less than 8 per cent, the commission, in the exercise of its discretion, may modify the foregoing requirements of this ordinance in a manner that will result in the best possible utilization of the land to be subdivided, giving consideration to the topography of the land and the general character of the proposed subdivision.

The ordinance provides that the basis for requirements for street and roadway widths and design in hillside areas are the topography of the land and the density of development in terms of the proposed number of dwellings to be served by the street or roadway. It provides that in subdivisions or sections of a subdivision in which all lots have an area of a half acre or more: 1 street grades for minor residential streets may be increased to 20 per cent; 2 the dedicated width of a two-way street may be reduced to 40 feet, with a minimum pavement width of 26 feet; 3 the dedicated width of a one-way street can be reduced to 30 feet, with a minimum pavement width of 20 feet; 4 integral sidewalks and curbs may be permitted.

The special standards for streets in hillside subdivisions in the Fremont Ordinance seem to avoid the familiar problem that arises when standards for variances and special exceptions are not written into the ordinance.

Furthermore, by permitting the reviewing authority to consider each street on the basis of topography and the number of dwellings served, it should be possible to serve the public interest and at the same time allow the developer to vary from flat land street standards. From the standpoint of ease of administration, the best approach is probably to set a single, recognized standard, permitting a narrower-than-usual width for minor and collector streets.

On the other hand, if the planning agency establishes hillside zoning with rigid but different minimum lot sizes for different zones, the use of street standards varying with lot size is probably more appropriate. The preceeding examples indicate the direction in which planning agencies are moving in modifying improvement requirements for hillside areas and other large-lot subdivisions. In some cities, pavement width requirements for minor streets have been reduced to as little as 20 feet for hillside and large-lot subdivisions.

If parking can be successfully handled through such devices as parking bays, minor streets with only two narrow moving lanes seem reasonable.

Design standards and improvement requirements for horizontal and vertical street curves, grades, curbs, and sidewalks may also be modified in hillside areas.

Because of the winding nature of hillside roads, it is probably desirable to allow sharper horizontal curves there than on minor streets in flat land subdivisions — possibly as short as a foot radius. Grades, too, may be allowed to depart from normal limits; they may be steeper, but only for short, straight stretches.

Requirements for curbs and gutters should also be checked. Although it may be feasible to omit straight curbs in flat land, large-lot developments substituting either rolled curbs or paved valley gutters , straight curbs are absolutely necessary on hillside streets if parking is even a possibility.

To hold a car on a steep grade, drivers must be able to park their cars with tires against a straight curb. The Contra Costa County ordinance requires straight curbs in any block in which the grade is more than 6 per cent. Curbs are also an important means of controlling street drainage; erosion of the roadside on steep hills is a major problem. These standards require: 1 assurance of maximum structural safety and slope stability; 2 use of the natural terrain; and 3 replanting of vegetation.

Disturbance of ridge and tree lines, grading, cuts, fills, and other potentially destructive actives are also regulated. This section is intended to protect the public from the potential negative impacts of erosion, siltation, pollution of water supplies, slope failure, increase in downstream run-off, alteration of scenic views, and destruction of potentially significant habitat, which may result from disturbance of steep slopes.

However, in areas of poorly drained soil, surface water may not run-off; frost pockets are common characteristics of low-lying land on slight slopes; wetlands also are usually found in the areas of this slope category.

Areas with a 3 to 8 percent slope are normally free from most development problems. Slopes with an 8 to 15 percent grade are typically acceptable for development. Some problems may arise as the slope increases. Difficulties with road and driveway construction, installation of sewage disposal facilities, storm water run-off, soil erosion, and increased construction costs are some of the limitations that can be overcome with careful site planning.

Land areas containing a 15 to 25 percent slope present considerable development limitations, which can be overcome only at a great expense to developers, adjoining property owners, the [municipality], and the environment.

Some of the problems encountered include soil erosion, malfunctioning septic systems, increased requirements for cut-and-fill operations, and vegetative cutting. Slopes greater than 25 percent present extremely serious problems, of the sort outlined above, for any type of development. Steep slopes and adjacent watercourses and wetlands have been and are in jeopardy of being damaged and destroyed by unregulated filling, excavating, building, clearing and grading, and other such acts inconsistent with the natural conditions of steep slopes.

Steep slopes in the [municipality] are environmentally sensitive landforms and valuable natural resources, which are of benefit to the entire [municipality] and the surrounding region. The environmental sensitivity of steep slopes often results from such features as rock outcrop, shallow soils over bedrock, bedrock fractures, groundwater seeps, watercourses, and other wetlands found on or immediately adjacent to steep slopes.

Protection of steep slopes is a matter of concern to the entire [municipality]. The establishment of regulatory and conservational practices in this critical area is needed to protect the public health, safety, and general welfare. Experience has demonstrated that effective protection of steep slopes requires preservation wherever possible.

Experience has further demonstrated that where steep slopes have to be disturbed, careful review and regulation — including stringent mitigating measures — are required. Erosion and sedimentation often include the loss of topsoil, a valuable natural resource, and can result in the disturbance of habitats, the degradation of the quality of surface water, the silting of wetlands, the alteration of drainage patterns, obstruction of drainage structures, and the intensification of flooding.

Steep slopes, including vegetation on rock cliffs, are an important environmental feature that contribute to the character of the [municipality].

Overdevelopment or improperly managed disturbance are detrimental to the character of the [municipality] and can result in public and private expenditures for corrective measures.

Regulation of development on steep slopes is consistent with the legitimate interests of landowners to make reasonable use of their land. Regulation can prohibit the degradation of steep slopes and allow reasonable use of private property by encouraging flexible design of development so as to avoid disturbance of steep slopes. Regulation can also permit environmentally sound disturbance of steep slopes conducted in accordance with acceptable management and engineering practices to permit reasonable use of private property.

Regulation of development on steep slopes will not preclude the [municipality] from continuing to meet its social, economic and other essential responsibilities, particularly its responsibility to provide affordable housing. In order to ensure the availability of affordable housing, the [municipality] has adopted many provisions in Chapter , Zoning and Chapter , Subdivision of Land, which enable the development of a variety of housing types to meet the needs of [municipality] residents for affordable housing.

These provisions allow the renting of rooms within homes and the development of accessory apartments, two-family and multifamily dwellings, boardinghouses and housing for senior citizens. The [municipality's] master plan recommends additional measures to promote affordable housing, such as the development of new villages or hamlets and senior citizen complexes in which affordable housing would be required.

Real estate sales data shows that housing prices in the [municipality] are among the lowest in Westchester County, indicating that the [municipality] has been successful in meeting its responsibility to provide affordable housing. These regulations are enacted with the intent of providing reasonable balance between the rights of the individual property owner to the fair use of his property and the rights of present and future generations.

Therefore, this chapter recognizes the rights of owners of property exhibiting steep slopes to use their property for reasonable purposes consistent with other regulations and controls, provided that such use, in the judgment of the appropriate agencies or officials of the [municipality], does not result in a significant loss or degradation of steep slopes or a loss of visual or open space benefits which steep slopes have been found to provide. As used in this chapter, the following terms shall have the meanings indicated:.

Customary Landscaping - Land maintenance involving tree trimming and pruning, the removal of dead and or diseased vegetation, lawn and garden care and the planting of decorative trees, shrubs, and plants. Disturbance - Excavation or fill or any combination thereof and shall include the conditions resulting from any excavation or fill. Excavation - Any act by which earth, sand, gravel, rock or any other similar material is cut into, dug, quarried, uncovered, removed, displaced or spread.

Fill - Any act by which earth, sand, gravel, rock, or any other material is deposited, placed, replaced, dumped, transported, or moved by person or persons to a new location. Measurements shall be made along a horizontal plane. Angle of repose - The maximum angle at which the exposed face of various soil and rock minerals can deviate from the horizontal without incurring the likelihood of a slope failure. Applicant - A person requesting a steep slope permit from the [municipality] in accordance with the provisions of this chapter.

Approving authority - The municipal agency or public official empowered to administer the permit procedures of this chapter. Clearing - Any activity which removes or significantly disturb trees, brush, grass, or any other type of vegetation. Deposit - To fill, place, eject, or dump any material not including storm water. Disturbance - The removal of vegetation or the filling, excavation, regrading, or removal of soil, rock or retaining structures in areas of steep slope, whether by manual labor, machine, or explosive.

Disturbed area - Any steep slope area for which a disturbance is proposed or is ongoing. Drainage - The gravitational movement of water or other liquids by surface runoff or surface flow.

Erosion - The wearing away of the land surface by action of wind, water, gravity, or other natural forces.

Excavation - Any activity which removes or significantly disturbs rock, gravel, sand, soil, or other natural deposits. Fill - Any act by which earth, sand, gravel, rock, or any other material is deposited, placed, replaced, pushed, dumped, pulled, transported, or moved by man to a new location and shall include the conditions resulting therefrom.

Forest land - An ecosystem supporting a dense growth of trees covering a large area. Fence rows alone do not constitute a forest system. Grading - The alteration of the surface or subsurface conditions of land, lakes, ponds, or watercourses by excavating or filling.

Mulching - The application of a layer of plant residue or other material for the purpose of controlling erosion. Person - Any person, firm, partnership, association, corporation, company, organization or other legal entity of any kind, including public agencies and municipal corporations. Removal - Cutting vegetation to the ground, leaving it as stumpage, extracting it completely, or killing it by spraying.

Sediment - Solid material, both mineral and organic, that is in suspension, is being. Site - A lot or parcel of land, or a contiguous one, where grading work is performed as a single unified operation. Site plan - The map or drawn representation of a proposed development, which is submitted to the municipal approval authority for consideration and approval. Site preparation - The activities of stripping, excavatimg, filling, and grading, no matter what the purpose of these activities.

Soil - The natural, unconsolidated, mineral and organic material occurring on the surface of the Earth; it is a medium for the growth of plants.