Our experience with vegetated roofs Shakopee Mdewakanton Sioux Community Prior Lake, Minnesota
Shakopee Mdewakanton Sioux Community Located in East Central Minnesota 3,000 acres of land at agriculture / urban interface. Cannot relocate. Future generations must live on existing land. Must consider environmental impact of development. Scott County, MN ") 21 282 tu 169 ")13 %&'( 35W
Sustainable building practices All possible items considered at planning stages Choose the ones that made the most sense for the project Vegetated roof Skylights Geothermal Solar water heat
What is a vegetated roof? A roof covered with soil and plants. Built to support weight of water, soil, and plants. Root barrier over normal roofing membrane. Drainage layer Filter fabric to hold soil, silt. Growing media Extensive <6in Intensive >6in
Why install a vegetated roof? Retain stormwater Reduce polluted waters Reduce runoff Reduce building footprint Reduce heat-island effect Minimize heating / cooling costs Increase roof life-span Provide wildlife habitat Aesthetics
SMSC Vegetated Roofs Two irrigation zones Irrigated with treated effluent Water Reclamation Facility 31,000 ft 2 Planted Summer 2006 Native and nonnative plants
SMSC Vegetated Roofs Six irrigation zones Dakotah!! Ice Arena 32,600 ft 2 Planted Fall 2008 / Spring 2009 Primarily Sedum Will interplant with native species Research area with moisture meters, tipping bucket, and controllable surface and subsurface irrigation.
Green Roof Sub Layer Both locations employ an Extensive Henry Green Roof System Hot applied, rubberized, seamless, flexible asphalt membrane Insulation DBR Rootbloc Keeps soil and roots from lower layers Prefabricated storage cones reduce runoff and provides moisture to plants Channels for aeration and drainage avenue for excess water
Soil Reclamation Facility Thickness 6 of growing medium 35% greater plant survival versus 4 thick Composition 10% pine bark, 30% sand, 60% haydite (high grade shale) Ice Arena Same thickness Composition 2% pine bark, 94% pumice and 4% stabilized compost Lighter and less expensive ($4.29 ft 2 versus $5.41 ft 2 ) Carbon footprint smaller Blended locally using pumice from Northern Cal. or Virginia
Maintenance SMSC to assume green roof maintenance for Reclamation Facility in 2009 and Ice Center in 2010 Staff member with dedicated time Irrigation lines Spring opening and fall shutdown Break repair Irrigation scheduling Plant composition If you care about the type of plants on the roof - plan on maintenance to remove and dispose of weeds
Cost Reclamation Facility $950,000 + load bearing modifications versus approximately $500,000 to $600,000 for traditional roof Maintenance $1,000 per year Heating and cooling approximately 1/3 of expected Ice Arena Changes to soil and plants types meant ft 2 cost was reduced from $11.99 to $7.76 (35.3%) Membrane to soil cost $16.5/ft 2 was reduced to $15/ft 2 Irrigation SMSC will reimburse enterprise for cost since this project was initiated by government staff
Plants: 1 st vegetated roof 25 Native species, 17,000 plants 12 non-native Sedum species, 25,000 plants 20 volunteer weeds, unknown # of plants Native, wild petunia Sedum kamtchatium Non-native native weed, Lamb s s quarter
What we are unsure about Are green roofs really better at moderating heating and cooling costs than conventional roofs? How much / how long is water retained? What plants give best performance? What about irrigation? Do wildlife really use this novel habitat?
SMSC Research Plant establishment via seeds, cutting, or plugs and various irrigation levels to determine optimization of upfront cost and final green cover. Determine plant and irrigation influence on soil moisture to optimize water retention. Looking at building heating and cooling on outside and inside of the WRF and an adjacent building without a green roof. Exploring pollinator usage of plants.
What we do know... There is less temperature swing between day/night temp on a green roof vs. conventional roof, but averages the same. Winter temperature: Conventional roof: air temperature Green roof: ~32 F Temperature monitoring Neighboring rock ballast roof
What we do know Animals are using the vegetated roof Solitary bee Blue-wing teal nest Jumping spider Beetle Bumblebee Sootywing butterfly
What we do know... Higher irrigation results in higher plant coverage. September 2007 ¾ a week September 2007 1 a week Natives and Sedum both do well under irrigation Many native and non-native plants volunteer Weeds provide green roof function
What we do know... If vegetated roofs are to function as an ecosystem, then the plants must be able to complete their lifecycle. Our irrigated plants are producing seed, but In Minneapolis, a 10-year old unirrigated vegetated roof is being hand-sown with seed due to poor performance. Partridge pea seedling Purple prairie clover seedling Green Institute Minneapolis, MN
What we don t know What are the optimal plants to use? Sedum are drought-tolerant succulents, used in European green roofs. Proven success. Few have explored the use of native plants. Poor success so far on species chosen. Must recognize that there is no natural equivalent to an engineered green roof. Yet habitats with thin soils should be looked at for native plants. Not commercially available.
What we don t know What is optimal green roof performance for stormwater retention? Do green roofs provide water storage without plants? Do species affect water storage or is it just total coverage of plants? Do irrigated plants retain more water than non-irrigation plants?
What we don t know What is optimal green roof performance for heating and cooling? Do they outperform conventional roofs? Will there be a benefit with or without plants? Midwest roofs are well insulated; there may be no direct link between roof temp and inside temp. How does drought affect green roof heating and cooling in the absence of irrigation? Are green roofs thermally invisible?
What we don t know What is optimal green roof performance for roof life-span? Conventional rock ballast roofs and vegetated roofs both block UV so no extra benefit here. Does the lack of swing in temperature really increase life-span of roof membrane? We won t know the answer for years.
What we don t know What is optimal green roof performance for wildlife usage? Wildlife is mostly insects and spiders, with limited bird use. Insects using both native and non-native plants. Native wildlife use more likely with native plants. Ducklings had to be rescued because there was no safe way off roof. (5 story drop)
Contacts Shakopee Mdewakanton Sioux Community (Prior Lake, MN) Shingobee Construction Co. (Loretto, MN) Rosenquist Construction Co. (Minneapolis, MN) Bolton and Menk, Inc. (Burnsville, MN) Aloha Landscaping (St. Paul, MN)
Questions? Green Institute Minneapolis, MN