Chapter 17.15
SUBDIVISION DESIGN STANDARDS
Sections:
17.15.020 General requirements.
17.15.010 Intent.
The standards and details of design herein contained are intended only as the minimum requirements so that the general arrangement and layout of a subdivision may be adjusted to a wide variety of circumstances. However, in the design and development of the plat, the subdivider should use standards consistent with the site conditions so as to assure an economical, pleasant and durable neighborhood, and shall conform with design standards as approved by the Board of Supervisors. [Ord. 39 § 4, 1996. Code 2009 App. B, § 4.]
17.15.020 General requirements.
A. Land Suitability. No land shall be subdivided for other than agricultural purposes which is found to be unsuitable for subdividing by reason of flooding, ponding, poor drainage, adverse soil conditions, adverse geological formations, unsatisfactory topography or other features likely to be harmful to the health, safety or general welfare unless such unsuitable conditions are corrected to the satisfaction of the County. Land with a land evaluation (LE) score from the LESA system below 40 points shall be considered unsuitable for development.
1. If a subdivision is found to be unsuitable for any of the reasons cited in this section, the Planning and Zoning Commission shall state its reasons in writing and afford the subdivider an opportunity to present data regarding such unsuitability. Thereafter, the Planning and Zoning Commission may reaffirm, modify or withdraw its determination of unsuitability.
2. Floodland. All lots located within a floodplain shall contain adequate area above the elevation of flooding for essential and planned installations. The disposition of all land in a subdivision which lies in a floodplain shall be as follows:
a. Included within individual lots in the subdivision; or
b. Reserved in open space for use by all owners of lots in the subdivision with an appropriate instrument providing for its care by such owners.
3. Subdivisions (including mobile home parks and subdivisions) shall be consistent with the need to minimize flood damages and shall have adequate drainage provided to reduce exposure to flood damage. Development associated with subdivision proposals shall meet the applicable performance standards. Subdivision proposals intended for residential development shall provide all lots with a means of vehicular access that will remain dry during occurrence of a 100-year flood.
B. Streets.
1. Private Streets. Private streets, not dedicated to and accepted by the County, are discouraged. If private streets are utilized, they shall be platted as such and be under the control of the subdivision, homeowners association, and/or subdivider. Private streets shall be platted with a minimum of 60 feet in width.
2. Continuation of Existing Streets. Proposed streets shall provide for continuation or completion of any existing streets (constructed or recorded) in adjoining property, at equal or greater width, but not less than 60 feet in width, and in similar alignment, unless variations are recommended by the Planning and Zoning Commission.
3. Circulation. The street pattern shall provide ease of circulation within the subdivision as well as convenient access to adjoining streets, thoroughfares, or unsubdivided land as may be required by the Planning and Zoning Commission. In a case where a street will eventually be extended beyond the plan but is temporarily dead-ended, an interim turnaround shall be required.
4. Street Intersections. Street intersections shall be as near to right angles as possible.
5. Cul-de-Sac. Whenever a cul-de-sac is permitted, such street shall be no longer than 600 feet and shall be provided at the closed end with a turnaround having a street property line diameter of at least 100 feet in the case of residential subdivisions. The right-of-way width of the street leading to the turnaround shall be a minimum of 60 feet. The property line at the intersection of the turnaround and the lead-in portion of the street shall be rounded at the radius of not less than 30 feet. A paved cul-de-sac without curb and gutter shall have a minimum paved diameter of 65 feet with a minimum shoulder width of three feet of rock. A paved cul-de-sac with concrete curb and gutter shall have a minimum paved diameter of 71 feet measured from the back of curb to back of curb.
6. Street Names. All newly platted streets shall be named in a manner consistent with the present street name system. A proposed street that is obviously in alignment with other existing streets, or with a street that may be logically extended though the various portions be at a considerable distance from each other, shall bear the same name. New street names shall be subject to the approval of the Planning and Zoning Commission and Board of Supervisors so as to avoid duplication or similarity of names.
7. Physical and Cultural Features. In general, streets shall be platted with appropriate regard for topography, creeks, wooded area, and other natural features which would lend themselves to attractive treatment.
8. Half Streets. Dedication of half streets will be prohibited unless there exists a dedicated or platted half street or alley adjacent to the tract to be subdivided, the other half shall be platted if deemed necessary by the Planning and Zoning Commission.
9. Alleys. Alleys may be required in business areas and industrial districts for adequate access to block interiors and for off-street loading and parking purposes. Except where justified by unusual conditions, alleys will not be approved in residential districts. Dead-end alleys shall be provided with a means of turning around at the dead-end thereof.
10. Easements.
a. Easements for utilities, when necessary, shall be provided along rear or side lot lines or along alleys. The width of such easement shall be not less than 10 feet in total width.
b. Whenever a subdivision is traversed by a watercourse, channel, drainageway or stream, a stormwater easement or drainage easement may be required. The width of such easement shall be adequate for the anticipated drainage but not less than 30 feet and shall be shown on the plat.
c. For minor subdivisions, any lot which has no frontage upon a public or private street shall be provided with an easement for access to a public or private street. For one single-family dwelling, there shall be an exclusive unobstructed private easement of access of at least 20 feet. For two such single-family dwellings, there shall be a common easement of access at least 24 feet. For three or more single-family dwellings, there shall be a common easement of access at least 30 feet. Lots in a major subdivision shall have adequate frontage along a dedicated street, either public or private.
d. Easements to the County for road purposes shall not be allowed.
11. Neighborhood Plan. If any overall plan has been made by the commission for the neighborhood in which the proposed subdivision is located, the street system of the latter shall conform in general thereto.
12. Unsubdivided Portion of Plat. Where the plat to be submitted includes only part of the tract owned by the subdivider, the Planning and Zoning Commission may require a sketch of the prospective future system of the unsubmitted part. The street system of the part submitted shall be correlated with the street system of the part not submitted.
13. Major Thoroughfares. Where a new subdivision, except where justified by limiting conditions, involves frontage on a heavy traffic way, limited accessway, freeway, or parkway, the street layout shall provide motor access to such frontage by one of the following means:
a. Be so arranged as to permit, where necessary, future grade separations at highway crossings of the railroad.
b. Border the railroad with a parallel street at a sufficient distance from it to permit deep lots to go back onto the railroad; or form a buffer strip for park, commercial, or industrial use.
14. Street Width. The width of minor or residential streets shall not be less than 60 feet.
15. Street Alignments. Streets and alleys shall be completed to grades which have been officially determined or approved by the Board of Supervisors. All streets shall be graded to within two feet of the right-of-way and adjacent side slopes graded to blend with the natural ground level. The maximum grade shall not exceed seven percent for main and secondary thoroughfares, or eight percent for minor or local service streets. All street alignments, both horizontally and vertically, shall meet design criteria as specified in the sixth edition of the American Association of State Highway and Transportation Officials (AASHTO) Policy on Geometric Design of Highways and Streets.
16. Culverts and Crossroad Drainage Structures. Driveway culverts shall be designed for a 25-year flood, or a minimum of 15 inches in diameter. Crossroad drainage structures shall be designed for a 50-year flood, or a minimum of 24 inches in diameter. [Ord. 132, 2014; Ord. 81, 2003; Ord. 75, 2002; Ord. 39 § 4(A), 1996. Code 2009 App. B, § 4(A).]
17.15.030 Blocks.
A. No block shall be longer than 1,320 feet.
B. At street intersections, block corners shall be rounded with a radius of not less than 25 feet. However, where a curve radius has been previously established, such radius shall be used as standard if greater than 25 feet. [Ord. 39 § 4(B), 1996. Code 2009 App. B, § 4(B).]
17.15.040 Lots.
A. Corner lots shall have a minimum width that will permit required building setbacks on both front and side streets.
B. Double-frontage lots, other than corner lots, shall be prohibited except where such lots back onto a major street or highway.
C. For the purpose of complying with minimum health standards and zoning requirements, the following minimum lot sizes shall be observed:
1. Lots which cannot be reasonably served by a public sanitary sewer system and public water supply mains shall have a minimum width of 150 feet, measured at the building line, and an area of not less than one and one-half acres. For major subdivisions created after August 20, 2002, the effective date of Ordinance No. 75, no lot shall be created unless public sanitary sewer and public water is available or may be extended at the time of development.
2. Lots which are connected to a public water supply main or are connected to a public sanitary sewer system shall have a minimum width of 80 feet and an area of not less than 15,000 square feet.
3. Lots which are connected to a public water supply main and to a public sanitary sewer system shall have a minimum width of 75 feet and an area of not less than 7,500 square feet.
D. Side lot lines shall be approximately at right angles to the street or radial to curved streets. On large size lots and except when indicated by topography, lot lines shall be straight. [Ord. 75, 2002; Ord. 39 § 4(C), 1996. Code 2009 App. B, § 4(C).]
17.15.050 Improvements.
A. Streets and Roads. In addition to BHCC 17.15.020(B), all streets or roads intended to be dedicated to public use and accepted into the County secondary road system shall meet the following criteria:
1. All streets shall be put to grade and standard cross section according to the plans approved by the County Engineer and Board of Supervisors prior to construction. Either a rural (see Figure 2) or urban (see Figure 3) type cross section may be used. Both plan and profile view details shall be drawn to a scale of one inch equals 100 feet horizontal and one inch equals 10 feet vertical.
2. Paved streets without curb and gutter that incorporate open ditches as a means of stormwater drainage shall have a minimum surfaced width of 24 feet with a minimum shoulder width of three feet of rock (see Figure 2). Paved streets with concrete curb and gutter shall have a minimum width of 31 feet measured from the back of curb to back of curb (see Figure 3).
3. All streets shall be paved with one of the following in accordance with specifications approved by the Board of Supervisors and County Engineer:
a. Class B Portland cement concrete paving with a minimum six-inch thickness with a two percent crown measured from the centerline of the street to the gutter or shoulder of the road.
b. Asphaltic concrete paving with a minimum six-and-one-half-inch thickness, as follows, with a two percent crown measured from the centerline of the street to the gutter or shoulder of the road.
i. Surface course: two and one-half inches of Type A asphaltic concrete.
ii. Base course: four inches of asphalt treated base or four inches of Type B asphaltic concrete.
iii. Subbase course: four inches of soil aggregate subbase.
c. Other alternative construction materials and specifications acceptable to the Board of Supervisors and County Engineer.
d. All construction and materials shall conform to the current Iowa Department of Transportation standard specifications and special provisions.
4. Advance notice of construction is required.
5. All designs, materials, inspection, results, and procedures shall be certified to the County Engineer by a duly registered engineer.
B. Utility Service Systems.
1. Public sanitary sewers and water systems shall be installed within the street or right-of-way or established easements as required by the state and local ordinances.
2. Gas mains shall be installed within the street right-of-way or an established easement.
3. Electric and telephone lines shall be installed within the street right-of-way or established easements.
4. All utility service systems shall be subject to approval by the County Engineer and Board of Supervisors.
C. Storm Drainage.
1. Adequate storm sewers and inlets shall be provided where necessary.
2. Natural waterways shall be maintained and protected.
3. All stormwater facilities shall be subject to approval by the County Engineer and Board of Supervisors.
D. Utility Locations. The proposed location, alignment and sizes of all utilities, whether underground or overhead, and the type of street construction shall be shown on the preliminary plat. Approval of the plat will form the basis for final designs of all improvements.
All underground utilities to be located within the street right-of-way shall be constructed and service provided to each lot before paving of the street.
E. Signs. Street signs that conform to the Manual on Uniform Traffic Control Devices (MUTCD) shall be installed by the developer at all intersections.
F. Mailboxes, Including Newspaper Boxes. Mailboxes and mailbox construction shall conform to Black Hawk County Engineer and United States Postal Service standards.
G. Parking. The depth and width of properties reserved and laid out for residential, commercial, or industrial purposes shall be adequate to provide for the off-street parking and loading facilities required for the type of use and development contemplated, as established in the Black Hawk County zoning ordinance. [Ord. 39 § 4(D), 1996. Code 2009 App. B, § 4(D).]