Considering Decks as a Pervious Surface DESCRIPTION:
RECOMMENDATION:
The Village Board should discuss this item to determine if legislation should be prepared to modify Chapter 217 Section 7 of the Village Code.
SUMMARY:
This appeared as a discussion item on the Board of Trustees Meeting held on April 26, 2016. General Code provided two samples of zoning codes from municipalities in New York, Tarrytown and Cazenovia. Both Tarrytown and Cazenovia's Codes exclude open wood decks with spacing between floorboards from the definition of an 'Impervious surface' if they are located above a pervious surface (see attached).
Samples from zoning codes outside of New York which included similar definitions of an 'Impervious surface' also included Trenton, NJ and Elmhurst, IL.
The Village Planner, Marilyn Timpone-Mohamed of Frederick P. Clark Associates, was also consulted in the search for relevant legislation but was not able to find any additional sources.
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Article II. Terminology § 180-9. Definitions.
As used in this chapter, the following terms shall have the meanings indicated:
IMPERVIOUS SURFACE Any material placed on or above the earth that substantially reduces or prevents the natural percolation of precipitation and melted snow into the soil. Examples include but are not limited to structures, including eaves, roofs and roof overhangs; parking areas (whether hard-surfaced or not); driveways; sidewalks; patios and decks; sport courts; and pools. The following shall not be considered as impervious surfaces:
A. Wood decks less than 200 square feet, if constructed with a space between each plank and if the deck is constructed over a pervious surface (1/2 of the area of such wood decks exceeding 200 square feet shall be considered impervious surface);
B. Pathways six feet or less in width that employ grass pavers or porous paving and which are not intended for automobile use.
Village of Tarrytown, Chapter 305. Zoning
Article II. Definitions and Word Usage § 305-5. Word usage; terms defined.
A. Words stated in the present tense include the future, the singular includes the plural, and the plural includes the singular. The word "person" includes a corporation, partnership or other combination of persons. The word "lot" includes the word "plot." The word "building" includes the word "structure." The word "shall" is mandatory and not directory and does not indicate mere futurity unless the context clearly so requires. The words "Village Board," "Board of Appeals," "Planning Board," "Building Inspector" or "Code Enforcement Officer," "Village Attorney," etc., mean, respectively, such officers or boards of the Village of Tarrytown. The term "Board of Trustees" means the Village Board. The term "certificate of compliance" means "certificate of occupancy." The term "occupied" or "used" as applied to any land or building shall be construed as though followed by the words "or intended, arranged or designed to be occupied or used." B. Unless otherwise expressly stated, the following terms, for the purpose of this chapter, shall have the meanings herein indicated. For purposes of clarity and uniformity throughout this chapter of the Village Code, some definitions may be regulatory in nature.
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Sample Legislation Compliments of General Code
DECK An outdoor platform attached to the principal structure of a building and built above the natural grade. A deck does not have a roof and is exposed to the elements.
IMPERVIOUS COVER Those surfaces, improvements and structures that cannot effectively infiltrate rainfall, snow melt and water (e.g., building rooftops, pavement, sidewalks, driveways, etc.).
IMPERVIOUS SURFACE AREA The sum of the area of coverage or footprint of all buildings, structures, paved areas, patios and other improved surfaces on a lot preventing natural runoff from percolating to the ground, measured in square feet. Areas paved with gravel, crushed stone and other pervious materials shall not be considered impervious. Open wood decks with spacing between floorboards shall also not be considered impervious if they are located above a pervious surface. Calculation of the total impervious surface area on a site shall be based upon the gross lot area, not the net developable area on a site.
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Maine Legislature Title 38: Waters And Navigation, Chapter 3: Protection and Improvement of Waters, Subchapter 1: Environmental Protection Board, Article 5-A: Natural Resources Protection Act Heading, §480-B. Definitions
5-B Impervious area. “Impervious area” means an area that is a building, parking lot, roadway or similar constructed area. “Impervious area” does not mean a deck or patio. (updated 2011)
Elmhurst, IL Code of Ordinances Article II- Building and Constriction Requirements, 24.10 - Impervious Surface Regulations for Residentially Zoned Properties (Updated 2014)
a. Impervious Surface Definition. Impervious surface is land covered that cannot effectively absorb or infiltrate water, including, but, not limited to, non-porous asphalt or asphalt sealants, non-porous concrete, roofing materials, and gravel surfaces used as roadways or parking lots. (1) "Impervious surfaces" shall also include:
(ii) Wooden or composite planked decks and patios without spacing between the planks and impervious area underneath;
(2) "Pervious surfaces" shall include: (iii) Wooden or composite planked decks and patios with spacing between the planks and permeable area underneath;
Becker County, MN Zoning Ordinance, Chapter 3- Nonconformities, Section 11- Mitigation Requirements for Nonconformities in Shoreland Areas B. Calculation of mitigation requirement units. The calculation of required mitigation units shall be based on the following provisions.
1.) Nonconforming impervious surface. Impervious surface is not allowed to exceed twenty-five percent (25%) coverage. Impervious surfaces include, but are not limited to:
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streets, roofs, sidewalks, driveways, parking lots, and similar facilities and areas covered with gravel, concrete, bituminous, compacted sand, lime rock, clay or other surfaces that substantially reduce or prevent the infiltration of water. Surface coverage between fifteen percent (15%) and twenty-five percent (25%) is allowed with offsetting mitigation. Each percentage point of impervious surface greater than fifteen percent (15%) represents five (5) mitigation requirement units.
(1) Pervious decks. Decks shall be considered pervious if all of the following conditions are met: (1) Maximum material (board) width is eight inches (8”); Becker County Chapter 3 Zoning Ordinance 17
(2) Minimum spacing between material (boards) is one-quarter inch (1/4”); and
(3) The area under the deck is pervious material.
Decks not meeting these requirements shall be considered as impervious.
Wake County, North Carolina 2009 Wake County Hazard Mitigation Plan, Appendix E- Glossary Impervious Surface- A surface resulting from human activity that obstructs or prevents infiltration of water into soil. Impervious surface includes, but is not restricted to: buildings and rooftops; walkways, driveways, and parking areas that are paved or compacted by pedestrian or vehicular traffic; solid decks and patios; pavement; recreation facilities that are paved or compacted; and any other paved, compacted, or partially impervious surface. For purposes of calculating the percentage of impervious surface coverage, the area of the perimeter of the lot or parcel shall be regarded as the actual area of the lot or parcel. The water surface of a lake, pond, or swimming pool is not considered impervious. A wooden slatted deck is not considered impervious if the area below the deck is treated to prevent erosion and compacting of the soil below the deck. "Pervious" asphalt and "pervious" concrete are considered impervious if the surface's perviousness is expected to decrease under normal use or its subbase is compacted, as determined by the Engineering Division, Department of Community Development Services.
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From: Susan Epstein <susanrepstein@hotmail.com> Sent: Tuesday, March 29, 2016 3:41 PM To: Christopher Bradbury Cc: Michal Nowak Subject: permeable discussion
Follow Up Flag: Follow up Flag Status: Completed
RESEARCH: HERE IS THE LAST EMAIL: It is important to define “structure” specifically so that landowners and zoning staff are clear on what is and is not included. The definitions above do not address : • walkways • steps • sidewalks • fences • dog houses • bird houses • mail boxes • flag poles • fire rings • wood piles Types of surfaces to consider when crafting your impervious surface definition 3 Garrison, Paul et al. Implementation and interpretation of lakes assessment data for the Upper Midwest. Final report to the U.S. EPA. Grant No. X783254601. November 2008. pp.4748 4 www.sawyercountygov.org/Departments/ZoningandConservation/tabid/70/Default.aspx WCCA | NR 115 Guidebook 2-7 Some counties considered these surfaces to be impervious and some considered them pervious. 1. Open decks with at least a 1/4 inch space between deck boards with a pervious surface below. Many counties considered this to be pervious. 2. Grasscrete, pavers with voids that are filled with soil and then planted. If properly installed and vegetated correctly these can be considered pervious. 3. Gravel. Typical gravel materials used for roads and parking lots are engineered and compacted to withstand heavy loads. These compacted gravel materials form a seal through which water will not readily infiltrate. Runoff from gravel is similar to paved surfaces with only a slight reduction in runoff. It would be difficult to call a typical gravel driveway pervious. Many counties consider this to be impervious. 4. Permeable Paver System. The key word here is system. The pavers are just a cap for the pervious system below. They are expensive and need to be installed properly and maintained. The WCCA shoreland committee has concerns about products that are marketed as pervious and depend on installation, maintenance and longterm compliance. If counties are going to allow the pervious pavers, they should consider an operation and maintenance
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agreement. Product representatives have recommended that onsite inspections should be required to ensure proper installation, and to ensure proper maintenance is occurring at 5 and 10 years. They require that contractors or product representatives ensure the systems stay pervious. Some counties consider permeable paver systems to be pervious and others do not. Pervious Decks Portions of pervious residential decks can be exempted from land coverage calculations. A deck is considered pervious if it has gaps that allow water to pass freely to gravel underneath, designed in accordance with the Best Management Practices Handbook available at www.tahoebmp.org. Process and criteria: • BMPs can be currently installed and certified or installed and certified along with this project. • This coverage exemption can only be authorized through a TRPA Single-Family project permit. • Remove all non-verified coverage, and mitigate 100 percent of any verified excess coverage. • Use the attached worksheets to help determine the pervious deck coverage exemptions available on your property. Overhang Allowance (“Height Reduction”) If the edge of a structure, such as a deck, eave or porch roof, is high enough to expose a significant portion of the ground underneath to sun, snow and rain, then not all of it needs to be counted as land coverage. Process and criteria: • Allowed on any Qualified Exempt or permitted project. • Calculate the reduction at a 3:1 ratio for decks and other structures that are raised above ground level. For every three feet above ground (measured to the bottom of the structure), one foot of the horizontal overhang dimension may be excluded from land coverage calculations (see illustration below). • This “height reduction” provision is applied to both existing structures and new structures and should be accounted for in your land coverage calculations. • Please note that the height reduction for structures on a slope may vary from corner to corner. • This reduction should be calculated on any deck or overhang more than one foot above the ground. • This reduction should be taken prior to calculation of exempted coverage. 12’ 8’-3’=5’ 9’ 5’ 8’ 6’ Actual land coverage associated with the deck: = 5’ x 6’ (30 sq.ft.) 3’ 5’ TRPA-CovExempWorksheet 4 of 9 06/13 RESIDENTIAL COVERAGE EXEMPTION http://www.hamilton.govt.nz/our-council/council- publications/manuals/Documents/Three%20Waters%20Management%20Practice%20Notes/HC C07%20-%20Permeable%20Surfaces.pdf
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Calculating Site Imperviousness
Epstein Original Email