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Attachment 1- Pervious Pavers (062617 cc ws pp KFS) w CITY OF ClIANIIASSEN � ;��� Chanhassen is a Community for Life-Providing for Today and Planning for Tomorrow VI! MI I MEMORANDUM TO: Todd Gerhardt, City Manager FROM: Paul Oehme, Director of Public Works/City Engineer DATE: September 25, 2017 SUBJ: KFS: Research Policies and Potential Consequences for the Allowance of Permeable Pavers in the Equation for Hard Cover Allowance DISCUSSION Annually,the city receives requests from residents that wish to install a patio or other hard cover on their property but the hard surface coverage threshold is sometimes already at the maximum allowed by code. Patios are considered hard surface and would add to the total hard surface coverage of the property. Hard Surface/Lot Coverage Percentage as PUD City Code (Chapter 20 - Zoning/Article VIII. Planned Unit Development District. Division 1.- Generally. Sec. 20-505 - Required general standards, (e)) illustrates by table the following: Hard surface coverage shall be limited as follows: Comprehensive Plan Designation Hard Surface Coverage (%) Low or medium density residential 30 High density residential 50 Office 70 Commercial (neighborhood or community) 70 Commercial (regional) 70 Industrial 70 Mixed use 70 According to Code, individual lots within PUD's may exceed these standards if the average meets these standards. Hard Surface/Lot Coverage Percentage by Land Use Classification Most directly related to the policy implications of addressing PICP, "maximum lot coverage" as a percent of the lot. PH 952.227.1100• www.ci.chanhassen.nln.us• FX 952.227.1110 7700 MARKET BOULEVARD • PO BOX 147 • CHANHASSEN • MINNESOTA 55317 I Todd Gerhardt KFS: Allowance of Permeable Pavers September 25, 2017 Page 2 of 8 Maximum Lot Coverage by Land Use Classification Land Use Classification by District Maximum Lot Coverage by Percentage "A-2" Agricultural Estate* 20 "RR" Rural Residential* 20 "RSF" Single-Family Residential* 25 "R-4"Mixed Low Density Residential* 30 "RLM" Residential Low and Medium Density* single-family dwelling, 35 two-family dwelling, 40 townhouse or multi-family dwelling 50 "R-8" Mixed Medium Density Residential* 35 "R-12"High Density Residential* 35 "R-16" High Density Residential* 50 "BN"Neighborhood Business 65 "BH" Highway and Business Services 65 "CBD" Central Business No maximum "CC" Community Commercial 70 "BG" General Business 70 "BF" Fringe Business 40 "OI" Office and Institutional 65 "IOP" Industrial Office Park 70 day care facilities 65 Shoreland Management District single-family residential 25 medium/high density residential 35 industrial zones within Lake Susan Shoreland District 70 *Please be apprised that City Code (Chapter 20-Zoning, Article IV. - Conditional Uses. Division 3. -Standards for Agricultural and Residential Districts. Sec 20-254. - Churches (4). states, "No more than 70 percent of the site is to be covered with impervious surface and the remainder is to be suitability landscaped in conformance with Article XXV." To get around the hard cover coverage requirement, property owners have asked to use patio systems that allow water to infiltrate into the soil to reduce runoff. Permeable pavers are the most previlent system that property owners have asked to be used. The City Code does not recognize these systems as permeable. Property owners would have to go through a variance process to have these systems approved. Todd Gerhardt KFS: Allowance of Permeable Pavers September 25,2017 Page 3 of 8 Staff has researched how other communites handle pervioius pavers for residental use in hard cover surface considerations. The attached spreadsheet shows the findings. Staff has been concerned that if allowed in residential areas, the systems may not be installed properly and not be maintained as needed. Staff does not have the resources to check back to see if the permeable pavers are working as intended. If they are not working as intended, what should the recourse be? The city does allow these systems in special situations for commercial or industrial areas however,plans have to be submitted and approved and a maintenance agreement signed. There were three main potential options to consider for residential areas: A Continue to define pervious pavers as impervious surface, with engineering and literature to support that policy. A Allow the conditional use of pervious pavers with engineering and literature to detail the conditions of use (e.g., engineering and maintenance standards, alternative management standards). • Allow the use unconditionally. There are several purposes for regulating and limiting impervious surfaces. Traditional city planning, zoning and code requirements set limits of impervious surfaces by land use classification to encourage infiltration and natural groundwater recharge,reduce urban flooding and solar heat gain, limit overall hardscape, and provide green space. Federal, state, and regional regulations have been enacted to manage stormwater in urbanized communities including but not limited to the requirements of the EPA Clean Water Act,National Pollution Discharge Elimination Systems (NPDES), and specifically Municipal Separate Storm Sewer Systems (MS4)requirements. In Minnesota,watershed districts (WD) and watershed management organizations were created to manage and protect the water resources within their defined hydrologic boundary. The Minnesota Legislature authorized the creation of watershed districts in 1955, through the Watershed Act, for the statutory purposes to conserve the natural resources of the state by land use planning, flood control, and other conservation projects for the protection of public health and welfare and the prudent use of natural resources. Further, in 1982,the Minnesota Legislature approved the Metropolitan Area Surface Water Management Act, which requires local units of government in the Seven-County Metro Area to prepare and implement comprehensive surface water management plans. Both the WD and the city have an interest in water quantity and quality and have adopted plans and rules that address a variety of water management concerns. More discussion with the WD would be need to see if allowing permeable pavers would be acceptable and comply with their rules. Todd Gerhardt KFS: Allowance of Permeable Pavers September 25,2017 Page 4 of 8 Pervious Pavers Defined The MPCA Stormwater Manual defines the more encompassing definition of permeable pavement as follows: Permeable pavements allow stormwater runoff to filter through surface voids into an underlying stone reservoir where it is temporarily stored and/or infiltrated. The most commonly used permeable pavement surfaces are pervious concrete,porous asphalt, and permeable interlocking concrete pavers (PICP). The Interlocking Concrete Pavement Institute(ICPI) describes permeable interlocking concrete pavements (PICP) as: PICP consists of solid concrete units molded with joints and/or openings that create an open area across the pavement surface. The openings allow water from storm events to flow freely through the surface into an open-graded base where it is collected and stored before it infiltrates into the underlying soils. For low-infiltration rate soils, drain pipes are often placed in the subbase to drain excess water, thereby functioning as a detention facility with some infiltration. Uses and Limitations of Permeable Interlocking Concrete Pavements (PICP) PICP has become the preferred permeable pavement option over pervious concrete and asphalt applications in recent years due in part to the use in smaller residential or retrofit applications, and lower material and installation costs and maintenance. Research has demonstrated that PICP is an effective method for reducing stormwater runoff and pollutants from urbanized areas. Properly designed, installed, and maintained PICP can have design life surface infiltration rates exceeding 100 in./hour according to industry literature. PICP are typically used in areas with light traffic at commercial and residential sites such as low- speed roads,parking lots, driveways, sidewalks,plazas, and patios. Stringent design, installation and maintenance is imperative to ensure proper performance. All the WD's recognize permeable pavement as a viable BMP to reduce volume and pollution. Many offer cost-share opportunities for their installation. However, complicating factors in the blanket use of PICP in the city are the varying rules and standards across the WDs pertaining to the design, installation, and maintenance of permeable pavement and PICP specifically. Each WD has its own specific rules, standards, and exemptions. Developing a city-wide one-size-fits- all set of engineering and maintenance standards for PICP is problematic. Therefore, the first step is to address the use of PICP in City Code if PICP are approved. Current City Code Definitions that Influence the Use of PICP A key issue that influences the use of PICP in the City Code is the varying definitions and regulations of impervious surface,hard surface coverage and lot coverage. City Code (Chapter 1- GENERAL PROVISIONS/Sec. 1-2. Rules of construction and definitions) defines impervious surface as: any material that substantially reduces or prevents Todd Gerhardt KFS: Allowance of Permeable Pavers September 25,2017 Page 5 of 8 the infiltration of stormwater. It shall include, but not be limited to, gravel driveways,parking area, buildings, and structures. City Code defines: A Hardcover as: the definition of impervious surface. A Lot coverage as: that portion or percentage of a lot that is covered by impervious surfaces. A Structures as: anything manufactured, built, constructed, erected, or a portion thereof which is normally attached to or positioned on land, whether temporary or permanent in character, including, but not limited to, buildings,fences, sheds, advertising signs, dog kennels, hard surface parking areas, boardwalks,playground equipment or concrete slabs. The terms "hard surface" and"hard surface coverage" are not defined within Sec. 102 Rules of construction and definitions,however the terms are interspersed throughout the Code. Watershed District Definitions that Influence the Use of PICP The following are definitions of impervious,pervious and structure for WDs within the jurisdiction of the city. In instances where definitions are not provided, the specific entity has not defined the term. The Minnehaha Creek WD defines impervious as: surfaces that are compacted or covered with a layer of material such that it is highly resistant to infiltration of runoff including but not limited to gravel, rock, asphalt, concrete, and non pervious paver systems. The Riley Purgatory Bluff Creek WD defines impervious surface as: any exposed surface that has been compacted or covered with a layer of material, or is likely to become compacted from expected, use, such that it is highly resistant to infiltration. The Carver County WMO defines impervious as: a constructed hard surface that either prevents or retards the entry of water into the soil and causes water to run off the surface in greater quantities and at an increased rate of flow than prior to development. Examples include rooftops, sidewalks,patios, driveways,parking lots, storage areas, and concrete, asphalt, or gravel roads. The Minnehaha Creek WD defines pervious as: surfaces that are readily penetrated or permeated by rainfall or runoff resulting in infiltration and reduced runoff. The Carver County WMO defines pervious as: a surface that is readily penetrated or permeated by rainfall or runoff resulting in infiltration and reduced runoff. The Riley Purgatory Bluff Creek WD defines structure as: any impervious building or other object that is constructed or placed on the ground and that is, or is intended, to remain in place for longer than a temporary period. Todd Gerhardt KFS: Allowance of Permeable Pavers September 25,2017 Page 6 of 8 The Carver County WMO defines structure as: anything constructed or erected on or connected to the ground. Current City Code that Influences the Use of PICP Relevant"hard surface" or"impervious surface"references and standards by zoning classification are cited here and in the Appendix. To ensure code changes are made to accommodate the use of PICP in the city, City Code sections should be thoroughly reviewed. City Code (Chapter 18 - Subdivisions,Article III. - Design Standards. Sec. 18-60. - Lots (j) states, Proposed house sizes shall be shown on the subdivision plan and shall be designed to accommodate residents' future house expansion(e.g.,porches) and accessory structures (e.g., decks and patios) as well as the driveway and sidewalks to building entrances. If house plans are not known, then a 60-foot by 60-foot building pad and a 30-foot wide access driveway shall be used. The maximum permitted impervious surface shall be calculated for each lot and the permitted houses and structures shall be limited to those sizes. Design, installation, and maintenance standards would be at the discretion of appropriate city staff and/or input or deferment to the corresponding WD or WMO. The MPCA Stormwater Manual suggests using the design, installation, and maintenance guidance for PICP as referenced by the Interlocking Concrete Pavement Institute(ICPI). The ICPI's website is www.icpi.org. It includes information for design professionals and installers regarding industry standards and specifications, installation guidelines and maintenance. Staff would recommend that if permeable pavers are allowed a certified installer shall be required to pull the permit. Many certified installers are available in the metro area. Shoreland Management and Bluff Creek Overlay Districts would need to be addressed in a different manner if ICPI are allowed. Staff recommends that as a permit requirement, a recordable easement or maintenance agreement be required that assures the owner of the property in which PICP was installed as a permitted accessory use is properly maintained as a pervious surface. Planning Department Review Planning staff has reviewed the findings from the research that has been completed. A brief discussion of these issues and Planning staff's recommendations are presented below. Issue 1: Lot Coverage and Impervious Surface Unlike the terms "hardcover" and "impervious surface", "lot coverage" and "impervious surface" should not be seen as interchangeable. When the City Code uses the terms hardcover and impervious surface, it is primarily in a context of stormwater management; however, the term lot coverage is has impacts on the intensity of land use, viewscape, and greenspace, as well as on stormwater runoff. Treating impervious surface and lot coverage as synonyms would Todd Gerhardt KFS: Allowance of Permeable Pavers September 25,2017 Page 7 of 8 mean that setbacks would be the only limit on the intensity of land use. In the case of industrial and commercial districts, this would allow for larger parking lots and buildings. Staff examined a site within the Southwest Corporate Center that is limited to 70%lot coverage. If lot coverage was defined solely as impervious surface and pavers were not considered impervious surface, the owner could increase the parcel's maximim building size from about 268,000 square feet to approximately 329,000 square feet and reduce the greenspace on site from 30 percent to about 10.5 percent. This would create a substantially different visual impact for surrounding land users and increase the development's traffic impact. In residential areas,this would mean that by substituting traditional impervious surfaces with pervious pavers, a builder could construct a house where only roofed structures counted towards lot coverage. This would allow for the construction of homes with a substantially larger footprint, as lot coverage currently used for driveways and patios could all be allotted to the house, and would also make it easier for large sheds to be constructed on small residential lots. Staff examined a property on W. 65th Street zoned Residential-Single Family and determined that if lot coverage was defined solely as impervious surface,the owner could reduce the property from having 75% greenspace to approximately 40% greenspace. Staff conducted the same exercise for a property zoned Residential Low and Medium Density on Strawberry Lane and discovered that the lot's greenspace could be reduced from 65%to around 31%. In both cases,the owners would be able to add 320 plus square foot sheds in their rear yards. The size of these accessory structures, overall intensity of property use, and visual impression of these residences would be very different from what is currently typical for the city's small lot residential neighborhoods. Since the city uses lot coverage as a major tool for limiting the intensity of development and preserving onsite greenspace, any change that completely exempts a category of materials from counting towards lot coverage will have many unintended consequences. Issue 2: Regulating through Conditional Use Permits Conditional Use Permits need to go before both the Planning Commission and City Council. Additionally, staff performs annual inspections of all conditional use permits in order to ensure that properties are complying with the conditions placed upon the permits. Categorizing pervious pavers as conditional uses would result in a significantly increased workload for both the Planning Commission and City Council, and performing the required inspections would exceed the capacity of the city's staff. Properties located in commercial and industrial districts can already utilize pervious pavers as part of a stormwater mitigation strategy. These systems are evaluated as part of a development's site plan review, and several projects incorporating these systems, for example Total Wine,have already been approved. Todd Gerhardt KFS: Allowance of Permeable Pavers September 25,2017 Page 8 of 8 Issue 3: Definitions Planning staff is concerned that by narrowly defining pervious systems as those made up of permeable interlocking concrete pavers,the city will not be able to take advantage of new technologies. Adopting a broader definition of pervious would allow the city to evaluate proposed systems based on their demonstrated capacity to facilitate stormwater infiltration, rather than the materials used in their construction. Summary Planning staff agrees that pervious pavers and other similar systems are proven technologies that are well suited for use in low traffic areas. Staff recognizes that the current lot coverage limits on residential properties were drafted partially with the intent of limiting the stormwater runoff generated in those zoning districts; however,the lot coverage standards were also created to create a certain neighborhood aesthetic. Staff desires to balance these two considerations to accommodate technologies that allow homeowners to created stormwater neutral structures, without comprising the character of the city's residential neighborhoods. Recommendation Planning staff recommends that the following changes be made to the City Code if permeable pavers are approved: 1) Residential properties should be allowed a total lot coverage of X+5%* where X is the currently established maximum impervious lot coverage, and the 5%is pervious lot coverage. To qualify as pervious,the system must be designed in compliance with standards established by the Interlocking Concrete Pavement Institute(ICPI) and installed by an ICPI certified installer.** a. Possible phrasing: "The maximum lot coverage for all structures and paved surfaces is 30%, of which no more than 25%may be impervious surfaces." 2) The use of permeable paver systems on industrial and commercial properties should continue to be addressed through the site plan review process. 3) The term"pervious/permeable"be defined in the City Code. 4) The usage of the terms "impervious" and"hardcover" should be standardized throughout the Code. *To provide context that would allow a 15,000 square foot lot(minimum RSF lot size)to construct a 750 square foot(25' x 30')pervious paver patio in addition to the currently permitted 3,750 square feet(25%) of impervious lot coverage. **For other types of pervious surface technologies, a similarly credible organization's guidelines and appropriately certified installer could be substituted. g:\plan\city code\2017\various\penneable payers.doc I