Planning and Zoning

CHAPTER 61 - LOT AND SITE DEVELOPMENT APPROVAL PROCEDURES

61.530 SITE CAPACITY CALCULATION:

Site capacity for any proposed development is equal to the net buildable area of the site multiplied by the density factor (in the case of residential uses) or by the floor area ratio (in the case of non‑residential uses).  The site capacity calculation provides the mechanism by which the total site area is adjusted to account for characteristics that constrain development potential.  The result is to determine the extent to which a site may be utilized given its unique physical characteristics.

61.531

Site Capacity Calculation Required: The site capacity calculation shall be completed for every type of development involving the erection of or addition to a building to determine the allowable amount of dwelling unit density (for residential use) or square footage of floor area (for all other uses).  Except within the Decorah Edge, where it is required for all development, the calculation need not be completed for any residential use type controlled by a lot size standard.  Site capacity calculations shall be based on the vegetation and topography of the site in 1991, as determined from 1991 USGS digital elevation model data and 1991 aerial photography or an equivalent or better source.  The density factor for all residential development in the Decorah Edge shall be as specified for performance residential development in the district, except that in the R-1 zoning district, the density factor shall be 5.5 for Type I residential development, 8.71 for Type II and 15.0 for Type III.

61.532

Capacity Calculation Procedure:  The following procedure is used to calculate the site capacity.

  1. Determine the Base Site Area:

    1. Base site area is calculated by subtracting the following areas from the gross site area, as determined by an on-site survey.

      1. Site area devoted to planned or existing right‑of‑way of arterials or higher order streets and required easements of access.
      2. Land that is not contiguous, including:


        1. Separate parcels that do not abut, adjoin, or share common boundaries with the rest of the development; and
        2. Land that is cut off from the main parcel by features such as a railroad, other existing land uses, or a major stream, such that common use is hindered.

      3. Lands that are reserved to satisfy requirements for storm water detention, usable recreation space or other open space use in a previously approved subdivision that has been partially or completely developed.

      4. Whenever a site contains land that is designated in more than two zoning districts, and the proposed development does not propose the integrated development of the site under the mixed-use provisions of the ordinance, the area zoned for non‑residential purposes must be subtracted to determine the area available for residential use.  (In the case of determining the area available for non‑residential use, subtract the area devoted to residential uses.)

  2. Determine the Amount of Resource Protection Land (All Land Uses): 

    All land area consisting of the natural resources or natural features listed below shall be measured.  The total acreage of each resource shall be multiplied by its respective open space ratio to determine the amount of resource protection land.  The resource protection ratio for lands exhibiting more than one characteristic shall be the highest single ratio applicable and not the sum of the ratios.  The sum total of all resource protection land on the site equals TOTAL RESOURCE PROTECTION LAND (see linked table).

  3. Determination of Site Capacity/Permitted Amount of Building: 


    1. The site capacity for residential density is determined by calculating the NET BUILDABLE AREA and multiplying this number by the density factor permitted in the applicable zoning district.  For residential uses types for which density factors are not provided, the density factors for performance residential development shall apply.  For the R-1 and R-Sa Districts, the density factor for performance residential developments applicable in the R-1x District shall apply. The calculation is as follows:   net buildable area table

    2. The permitted floor area for other uses in determined by calculating the NET BUILDABLE AREA, (adjusted to a square footage figure) and then multiplying this number by the floor area ratio permitted in the applicable zoning district.  The calculation is as follows:  permitted floor area calculation table

61.533

Density/Floor Area Bonuses: The net density or floor area achieved through the site capacity calculations may be increased through the preservation of certain natural features in the development.  The approving authority must make a finding during the review process that the design features justifying the proposed intensity increase have been provided in the development plan.  

  1. Preservation of Natural Features:  In the case of undisturbed slopes, woodland preservation, or preservation or restoration of other native habitats offered to achieve a density or floor area bonus, the development agreement must provide that the subject areas are protected from disturbance as a condition to approval of the permit authorizing the development.  The area to be left undisturbed on the site must be specifically identified on the plan and permit documents.  The area to be undisturbed on the site must be clearly marked and identified in the field prior to any development activity to insure that persons involved in the construction phase of the development do not disturb the subject area.  Protection from disturbance may be provided for through conservation easements, deed restrictions, or other mechanisms and shall provide for monitoring by a land trust or public agency.  Dedication of such areas as additional parkland beyond minimal required parkland dedication, where accepted, may be applied in density bonus calculations.
  2. Maximum Bonus:  The maximum achievable intensity must not exceed the density or floor area ratio factor for the applicable zoning district and the applicable approval process.
  3. Steep Slopes (slopes greater than 30 percent):  The net density or floor area   may be increased by multiplying the net amount by the percentage listed in the table below where steep slopes are left undisturbed.


    PERCENTAGE OF SITE IN STEEP SLOPES PERMISSIBLE % INCREASE IN NET DEVELOPMENT
    70% OR MORE 5% FOR EVERY 10% OF STEEP SLOPE AREA LEFT UNDISTURBED
    50% TO 69% 4% FOR EVERY 10% OF STEEP SLOPE AREA LEFT UNDISTURBED
    30% TO 49% 3% FOR EVERY 10% STEEP SLOPE AREA LEFT UNDISTURBED
    15% TO 29% 2% FOR EVERY 10% OF STEEP SLOPE AREA LEFT UNDISTURBED
    LESS THAN 15% 1% FOR EVERY 10% OF STEEP SLOPE AREA LEFT UNDISTURBED

  4. Moderate Slopes (Slopes of 18-30%):  The net density or floor area may be increased by multiplying the net amount by the percentage listed in the table below where moderate slopes are left undisturbed.

    PERCENTAGE OF SITE IN MODERATE SLOPES PERMISSIBLE % INCREASE IN NET DEVELOPMENT
    70% OR MORE 2.5% FOR EVERY 10% OF MODERATE SLOPE AREA LEFT UNDISTURBED
    50% TO 69% 2% FOR EVERY 10% OF MODERATE SLOPE AREA LEFT UNDISTURBED
    30% TO 49% 1.5% FOR EVERY 10% OF MODERATE SLOPE AREA LEFT UNDISTURBED
    15% TO 29% 1% FOR EVERY 10% OF MODERATE SLOPE AREA LEFT UNDISTURBED
    LESS THAN 15% 0.5% FOR EVERY 10% OF MODERATE SLOPE AREA LEFT UNDISTURBED


  5. Woodlands and Other Native Habitats:  The permitted number of dwelling units or permitted floor area may be increased by the percentage of the site area left as undisturbed woodlands or managed forest or as managed prairie, savanna, wetlands or other native habitats. [For example, if 50% of the site remains in undisturbed woodland after development, the permitted number of dwelling units would increase by 50%].
next page

Return to Top top

Page Last Modified On: Tuesday, February 12, 2008