"Surface with Purpose" Tool

Identifying opportunities for solar and green roof development for a more resilient region

The Surface with Purpose Tool quantifies potential climate-change mitigation effects from green roof and BioSolar development on large rooftops and surface parking lots across the Twin Cities region. Using multiple spatial datasets of the region's land use, county parcel records, and building footprints (2014-2016), the Surface with Purpose tool offers:

  • summary data on stormwater retention and annual solar energy production by jurisdiction (city, townships) or watershed, breaking out each metric by land use; and  
  • detailed property-level information, including address, ownership, total surface area, and annual solar energy production and stormwater retention estimates. 
The purpose of this tool is to 1) demonstrate the potential value of green roofs and BioSolar systems, 2) help communities and practitioners make more informed climate resilience investments, and 3) inform regional policy, planning, and development of these technologies to promote greater climate resilience across the region. 
For technical assistance or to learn more about this work, please contact Cameran Bailey (cameran.bailey[at]metc.state.mn.us).

Methods Summary

The following steps broadly outline how we built the dataset underlying this interactive. For more details, contact GIS Specialist Paul Hanson paul.hanson(at)metc.state.mn.us.
  1. Impervious surfaces were identified from the University of Minnesota’s Twin Cities Metropolitan Area 1-Meter Land Cover Classification (Urban Focused) dataset, then associated with other spatial layers, including: Metropolitan Council’s 2016 Generalized Land Use, Metropolitan Council's Regional Planned Land Use, county parcel boundaries, and Microsoft Building Footprint datasets. 
  2. From there, impervious surfaces that fell within Commercial, Office, Industrial, Multifamily Residential, Mixed Use, and Institutional* land uses were extracted (see below for definitions). That subset was then joined with the Metro Regional Parcel dataset to a) identify properties—that is, adjacent parcels with identical ownership and b) remove roadways. 
  3. Within this subset of impervious surfaces, the areas covered by buildings greater than 1,500 square feet were extracted and serve as the building component of the tool. The remaining impervious surface areas were further processed to identify surfaces that more closely align with large contiguous parking areas. These areas serve as the parking lot component of the tool.  
  4. Lastly, for each identified property, the estimated solar production and potential stormwater retention from 4”- and 6”-depth Green Roofs were calculated. 

*excluding "Religious Institution" as defined in the Metropolitan Council Regional Planned Land Use dataset.

Solar Production Formulas 

Annual Solar Productivity Formula

Kilowatt hours per year (kW-h/year) = Solar Radiance * (Surface area in square meters) * (365 days per year) * (generating capacity)


  • We chose a solar radiance value of 3.5 kW-hr based on the MN Solar Suitability Analysis App, a joint project between the University of Minnesota and the Minnesota Department of Commerce. 

  • Surface area selected include buildings with rooftops greater than 1,500 square feet and surface parking lots larger than 20,000 square feet.


Green Roof Development Formula

This formula is from the Minnesota Pollution Control Agency's Stormwater Manual—Green Roofs. 
Volume (V) = ((Surface area in square feet) * 0.75) * (Depth of media in feet) * (Moisture Content at Maximum Density (MMWR) in cubic feet/cubic foot)


  • We multiply surface areas by 0.75 to reflect our assumption that only 75% of any given roof or ground surface could be effectively converted to a green roof. 

  • Depth of media is equal to the area from the bottom of the media (top of underlying drainage layer) to the top of the media. 

  • We used a value of 0.33 based on its use in the Minnesota Pollution Control Agency's Minimal Impact Design Standards (MIDS) calculator

  • Surface area selected include buildings with rooftops greater than 1,500 square feet and surface parking lots larger than 20,000 square feet.

Land Use categories

For more information about the Regional Plan Land Use dataset published by the Metropolitan Council is available here. 

Single-Family Residential—Land used exclusively for residential purposes and containing a single dwelling unit; includes farmsteads, seasonal/vacation, single-family detached, and manufactured housing.

  • Farmsteads

    • Land that encompasses the single family residential dwelling and associated buildings of a farm.  Associated buildings of a farm may include buildings used for animal husbandry (barns, chicken coops, grain solos, etc.) along with accessory uses, provided that such accessory uses are incidental to the agricultural activities. 
  • Seasonal/Vacation

    • Land meeting the general definition of single-family residential containing a dwelling unit occupied seasonally or used as vacation property.  
  • Single-Family, Detached

    • Land meeting the general definition of single-family residential and detached from any other residential dwelling unit (i.e., with open space on all four sides, includes detached town homes). 
  • Manufactured Housing Park

    • Land meeting the general definition of Single-Family, Detached dwelling and designated for the placement of multiple manufactured housing structures. Note: this classification IS NOT used for an individual manufactured home. 

Multifamily Residential—Land used exclusively for residential multiple-family dwellings containing a building or multiple buildings. Includes single-family attached and multifamily.

  • Single-Family, Attached

    • Land meeting the general definition of multifamily residential containing two or more attached dwelling units (share a common wall, each with primary ground floor access to the outside regardless of the number of units or size.  Ex: Attached townhouse, double bungalow, triplex, etc. 
  • Multifamily

    • Land meeting the general definition of multifamily residential containing two or more attached dwelling units, one or more not having primary ground floor access to the outside. Ex:  Apartment building, condominiums or elderly housing – with minimal assisted living facilities – with a main entrance for all residents. 


  • Retail and Other Commercial

    • Land used for the provision of goods or services.  This category is for general sales and services that comprise the vast majority of establishments typically associated with commercial land use. This category is used as the default for commercial/retail land uses. Ex include: store, restaurant, hotel, bank, Metrodome, Excel Center – large commercial stadiums or arenas, Mini-storage, Canterbury Downs, YMCA, seasonal RV-Parks, American Legion, thrift stores (e.g. Goodwill, Salvation Army, etc) skeet clubs and outdoor gun ranges (large game/gun clubs  (80+ acres) should be Park, Recreation or Preserve). 
  • Office

    • Land used predominantly for administrative, professional, or clerical services.  Examples are, law offices, accounting firms, clinics (but not hospitals), and veterinarian clinic or hospital. 


  • Industrials and Utility

    • Land containing manufacturing, transportation, construction companies, communications, utilities (including water towers) or wholesale trade. This category includes publicly owned industrial lands (e.g. waste water treatment plant, see Special Situations below), warehouses (including commercial warehouses), automotive junk yards, and some special horticultural uses (large greenhouses that do not sell to the public).  
  • Extractive

    • Land containing extractive industry (Ex: Gravel Pits and Quarries). 


  • Institutional

    • Land used primarily for religious, governmental, educational, social, cultural or major health care facilities – patients with overnight stays (Ex: hospitals, schools, places of worship, cemeteries, city halls, museums, and county and state fairgrounds).  
    • NOTE: All land should be classified based on use NOT ownership! If land is owned by a church but appears to be Single-Family, Detached housing, say for the minister, or clergy, then the land use should be Single-Family, Detached residential NOT Institutional.  
    • Institutional category should include all publicly owned land that is not clearly in any other category (e.g. not in office, parks, or industrial, etc.). Clinics and health care facilities where there are only out-patient procedures will be classified as Office NOT Institutional. 

Mixed Use—Land containing a building with mixed uses.   


  • Mixed Use Residential

    • Land containing a building with multiple uses in combination with at least a residential unit(s). Examples include: Galtier Plaza in St. Paul, a mom & pop bakery with living space above it. 
  • Mixed Use Industrial

    • Land containing a building with multiple uses in combination with industrial uses and NO residential units. An example would be a building containing a warehouse, offices, and stores. 
  • Mixed Use Commercial and Other

    • Land containing a building with multiple uses but with NO residential units or industrial uses. An example would be a building containing commercial shops, childcare facility, offices, and/or restaurants.  Downtown areas usually have buildings where the first and/or second floor is commercial and the rest is office (e.g. Lawson Software Building), these types of buildings would be coded under this category. 

Park and Recreation 

  • Parks, Recreation, or Preserves

    • Land used for park and recreational assembly (Ex: community level ball fields, regional or small urban parks – public or private, playgrounds, rest areas, and other venues – indoors or outdoors – for sporting events or like purposes). Also includes passive activity uses such as park preserves, wildlife refuges, habitat area, public plazas, river walk, DNR owned land, greenways, and other public or private preserved land. 
  • Golf Courses

    • Land used for golfing, including driving range and practice areas and in most cases includes all land belonging to a country club if the predominant land use is golf course. 


  • Major Highway

    • Major roadway strips of land or area, on which a vehicular rights-of-passage exists under the following conditions: all interstate highways; all 4-lane divided highways with rights-of-way of 2,00 feet or greater in width; or all 4-lane roads with a Metropolitan Council functional class designation of "Principal Arterial."
    • NOTE: Where closely aligned frontage roads exist along vehicular rights-of-way which meet the preceding criteria, these frontage roads will be included in the total rights-of-way. Additionally, land uses occurring within a Major Highway rights-of-way, as specified above, but clearly has a different use (i.e., agriculture – row crops) are to be classified by its actual use. In addition, for consistency, if some major roadways that don’t meet the above criteria yet have been classified as a Major Highway in past land use dataset, will remain Major Highway. 
  • Major Railway

    • Land used and occupied or intended to be occupied by multiple railroad track lines or similar use including railroad classification, storage and repair yards, intermodal containerized freight and transload facilities, depots, etc. that could be classified under an industrial land use. 
  • Airport or Airstrip

    • Land used for the operation of aircraft and any related uses that are on the airport property (Ex: parking lot or car rental) Uses such as ball fields on the airport property would not be included in this category 


  • Agriculture

    • Land used for agricultural purposes. Includes discernable cultivation (Ex: ground tillage or crop rows) horticulture, floriculture (exotic flowers), viticulture (grapes) activities, pasture, and a broad range of other agricultural activities (Ex: horse boarding and training, kennels, sod farms, tree farms, fish production and processing, storage areas or buildings). Agricultural buildings (including feedlots) that are not part of the farmstead (see definition below) are included in this category. Note: Not all agricultural lands are discernable based on available data (aerial photography and assessors data).  Thus, a significant amount of agricultural land may be placed in the Undeveloped category. Previously, large feedlots were put in the industrial category.  


  • Undeveloped

    • Land not currently used for any defined purpose that may or may not contain buildings or other structures or has no discernable use based upon the aerial photos or available data. Undeveloped may include non-protected wetlands or lands currently under development. 
  • Open Water

    • ​A body of open water or flowing waterway inclusive within a discernable shoreline. This typically does not include wetlands or periodically flooded areas. Generally only features three acres or greater in size are to be delineated. Areas definable as another land use type will not be depicted as in the Water category (e.g. major highway bridge over a river and marina).  

Organizations & Technical Assistance

Minnesota Green Roofs Council

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The Minnesota Green Roofs Council (MGRC) maintains a list of companies and contractors experienced in the design and construction of green roofs. 


Minnesota Landscape Arboretum

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The Minnesota Landscape Arboretum serves as a research center and extension of the University of  Minnesota's College of Food, Agricultural and Natural Resource Sciences (CFANS). They host a Green Roof demonstration project. 

Tools & Calculators

Metropolitan Council's Solar Planning Resources

Solar Planning Resources.pngThe Metropolitan Council catalogues resources to support solar energy planning and implementation efforts. These resources include useful guides, organizations, and tools from across the State of Minnesota, the Upper Midwest, and the nation.


Twin Cities Greenhouse Gas Inventory

The Metropolitan Council's Twin Cities Greenhouse Gas Inventory is a tool that can assist local planning efforts in mitigating climate change. It summarizes the sources of emissions by jurisdiction and tracks how greenhouse gas emissions are changing over time. Communities can use the tool to explore how and where local actions and strategies can reduce future greenhouse gases. 


Metropolitan Council's Climate Vulnerability Assessment

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The Metropolitan Council's Climate Vulnerability Assessment (CVA) is a tool that can assist the Council and local planning efforts in preparing and adapting to climate changeCVA reveals what infrastructure, population, and operations, are most vulnerable to climate changes.

PV Watts Calculator

The National Renewable Energy Labratory's PV Watts Calculator estimates the energy production and cost of energy of grid-connected photovoltaic (PV) energy systems throughout the world. It allows homeowners, small building owners, installers, and manufacturers to easily develop estimates of the performance of potential PV installations.

Co-Benefits Risk Assessment (COBRA)

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The U.S. Environmental Protection Agency developed the COBRA screening tool to provide preliminary estimates of the impact of air pollution emission changes, translate this into public health effect impacts, and then monetize these impacts.

AVoided Emissions and geneRation Tool

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The U.S. Environmental Protection Agency developed a free tool (AVERT) to assess avoided emissions resulting from energy and renewable energy policies and programs.

ASU's Green Roof Energy Calculator

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This tool from the Urban Climate Research Center at Arizona State University allows users to compare the annual energy performance of a building with a green roof to the same building with either a dark or white roof. We recommend the following inputs for the Twin Cities region:

  • Growing Media Depth: 4” or 6”
  • Leaf Area Index: If building roof has little to no tree shade = 0.5
  • 75% coverage by Green Roof 
  • Electricity Cost ($/kW-h): $0.12
  • Natural Gas Cost ($/Therm): $.14

Case Studies & Further Research

Delivering Urban Resilience

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This report provides an in-depth analysis of the costs and benefits of applying smart surfaces (e.g. cool roofs, green roofs, solar PV, and permeable and reflective pavements) across three cities: El Paso, Philadelphia, and Washington, D.C. It assesses the capacity for these solutions to improve public health, strengthen resilience, and promote equity while saving billions of dollars.

Surface with Purpose launched in August 2020. We are currently collecting examples of how this tool is useful and related success stories from across the Twin Cities region. If you have a project or results to share, please contact Cameran Bailey (cameran.bailey[at]metc.state.mn.us).