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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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2
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