Kansas State University Memorial Stadium Green Roofs

• Protect the structural integrity of the two existing Memorial Stadium concrete seating and stairs/access areas and limit the number of people on each roof.
• Utilize green roofs to serve as a protective layer, increasing the life of the waterproofing membrane from 30 years to up to 50 years.
• Create a highly visible demonstration of Kansas State University commitment to environmental education and awareness and support sustainability efforts by providing building insulation, urban heat island mitigation, stormwater management, and habitat creation with a focus on butterflies and other pollinators.
• Create research opportunities for landscape architecture and other students and faculty at Kansas State University.
• Educate students, faculty, and staff on the design, implementation, management, functions, and benefits of green roofs.
• Create a well-functioning green roof requiring minimal maintenance (time, equipment, materials, and related costs) by university grounds staff.

• Dedicated in 1929, KSU Memorial Stadium honors the students and alumni who sacrificed their lives during World War I. An important aim of the green roof retrofit was to protect the structural integrity of the stadium by limiting the number of visitors on the seating and to reseal the roof for the buildings below, which were being renovated. The upper two-thirds of concrete seating and some of the existing leaky stairs were covered by insulation and waterproofing/roof protection materials.
• The two prairie-like green roofs cover the former seating areas on the east and the west side of the stadium, each encompassing approximately 21,525 sf for a total of 43,050 sf.
• Due to its light weight and insulation value, geofoam was used to fill in the rows of seating to create the slope. The resulting green roofs are steep with an approximately 20-degree or 36% grade.
• Both roofs are semi-intensive using a lightweight engineered sandy soil with a depth of 5 to 6 in. The east roof soil mix incorporates expanded shale to reduce its weight. Due to the steep slope, the soil is held in place by a durable nylon erosion mat that is secured to the upper part of each roof with stainless steel cables attached to eye-bolts.
• To sustain the plants on the green roofs, a spray irrigation system was installed.
• Because the pre-grown native prairie vegetative material envisioned by the designer was not available (due to the grower not being bonded), construction was adjusted to use native prairie seed and individual plants/plugs.
• The two green roofs were planted or seeded with a half-dozen grasses and 22 wildflowers indigenous to the U.S. tallgrass prairie, including blue grama (Bouteloua gracilis), sideoats grama (Bouteloua curtipendula), purple prairie clover (Dalea purpurea),and upright prairie coneflower (Ratibida columnifera). All but one of the plant species are native to the Konza Prairie, a tallgrass prairie nearby.
• The green roofs were identified by university researchers as an excellent location to study vegetative changes over time.  Vegetation studies were carried out to document species richness and dominance in late June 2016, 2017, 2018, 2019, and 2020 with future vegetation studies planned. 

Because the Memorial Stadium and adjacent K-State Alumni Center are used for a variety of activities, many thousands of people see the green roofs throughout the year. This provides an opportunity to visually and mentally connect these visitors to nearby prairie ecosystems in this part of Kansas and the Flint Hills Ecoregion.

However, at least one visitor has asked why weeds are growing on the two green roofs. The perception of plant aesthetics is influenced by knowledge, and also by how one views the natural world and the built environment. Those who do not understand why native grasses and wildflowers were planted on the green roofs may consider them to look “weedy”— unless they recognize the intentional connections being made to the prairie plant communities.

Ongoing maintenance adds another layer of complexity. Because the Memorial Stadium green roofs are in an urban setting, many volunteer plant species appear and must be managed. If these plant species are deemed to be a nuisance, they should be clipped or removed before their root systems become too extensive. 

Determining what species are a nuisance takes study and conversation with a wide range of experts and stakeholders. Different people have different perspectives on this matter, so developing a process for decision-making was important. Woody plants can be nuisance species because they undermine shallow green roof systems. Plants that cause allergic reactions or may cause injury are also a concern and should be removed.

• Roof slopes matter a great deal for soil moisture retention. Steep-sloped green roofs like the ones at Memorial Stadium shed water more quickly than flat green roofs and thus need more supplemental irrigation during warm, dry periods — typically each day during the first year of establishment and once or twice per week after the plants are established. Some irrigation is needed during dry periods that last more than a week to retain nearly full vegetative coverage and healthy plants. For the stadium green roofs, irrigation is needed to ensure near to full surface coverage by living plant biomass; however, irrigation is not needed every day now that the vegetation is established.
• Substrate types affect both structural load and moisture retention. The lighter-weight substrate on the eastern green roof (with expanded shale added to the sandy mix) dries out more quickly and typically has a wider range of moisture levels than the denser, nearly all-sand western green roof.
• Both plant survival and aesthetic concerns must be considered when selecting plants and determining irrigation regimes. Intense heat combined with the lack of rain during the growing season can dry out wildflowers on the stadium green roofs — especially those that require mesic soils and plants with larger leaves — causing plants to wilt and/or brown out above the substrate.
• Lack of early weed removal along with the lack of native grass seed has influenced species composition and vegetation coverage on the east green roof. The east plants looked very lush after abundant first-year irrigation but contained many agricultural weeds. These weeds were present due to one or more of the following: 1) weed seeds present in the sands harvested for the sandy substrate mix (this was the likely source of weeds like Eastern cottonwood and wild sweet clover); 2) weed seeds that blew onto the stored, uncovered substrates; and/or 3) weed seeds that blew onto stored, uncovered live plants. There is also evidence that birds drop thousands of seeds from the light towers at the top of the two green roofs. Attempting to pull large weeds disturbs green roof soils and creates bare spaces that encourage other weeds and pioneering species to establish.
• Despite some challenges, the vegetation has grown surprisingly well. A number of ecologists and biologists have been impressed that the native plants are doing so well on the steep slope. Vegetation on the west green roof looks less abundant than the east, but it contains a strong matrix of native grasses that make it look tallgrass prairie-like.
• The black erosion mat made of nylon mesh that was installed to hold the soil in place on the steep slopes over the surface of each green roof absorbs heat, makes it difficult for some plants to grow through, and has made weeding more challenging. It might have been wiser to use a biodegradable material for erosion control layering. The strong matrix of native grasses that are now established help to hold the soil substrate in place so the nylon mesh has become non-essential.
• Green roof construction requires active oversight, engagement, and persistent but respectful dialogue among designers, clients, and contractors. Because construction documents are contractual/legal agreements and can impact human health, safety, and welfare, designers and clients should work together to ensure that the provisions in these documents are met or formally adjusted if needed. Lack of contractor experience installing green roofs influences implementation and establishment practices and needs to be accounted for in the design and the construction process. Designers also need to be willing to listen and learn from the well-informed experience of contractors and nursery personnel.
• While physical and chemical soil testing during construction and post-construction are somewhat common, state-of-the-art biological testing was done on the Memorial Stadium green roofs. This project was the landscape architect’s first use of phospholipid fatty acid analysis (PLFA) to assess soil biological status. Samples were taken at least twice and PLFA indicated that some soil biology was active. Introducing and ramping up soil biological populations is an ongoing process for most projects. The landscape architect helped introduce beneficial microbes and collect substrates for assessment. Application of material to achieve humic balance has continued annually. The landscape architect will consider this process for certain future projects, which will help expand on the concept and guide future green roof design, implementation, and maintenance. 
• Ongoing management challenges at the Memorial Stadium green roofs include litter from users, damage to irrigation pipes through unanticipated uses like sledding on the roofs, and ground-dwelling wildlife that eat vegetation or burrow in the soil substrate.

Waterproofing Membrane: Hot Fluid-Applied Rubberized-Asphalt Waterproofing (American Hydrotech Monolithic Membrane 6125EV), bonded to underlying cement (gypsum board)
Protection Course and Root Barrier: 160-mil thick polyester reinforced modified asphalt sheet (with growth inhibitor)
Insulation: Extruded Polystyrene Rigid Board
Drainage Board: GSE TenDrain 300 mil Geocomposite
Soil/Substrate Containment System: Presto Geoweb GW30V6, with stainless-steel cables
Erosion Mat: Enkamat 7003 infilled with Flexterra (flexible growth material to assist with slope protection)
Drainage Channel (east MSGR/Welcome Center only): North American Green P550 
Drainage Channel (west MSGR/Purple Masque Theatre only): Hydroflex RBII beneath HyDroDrain 300
Organic fertilizer: Aggrand with Vermaplex™
Seeds and live plants supplier: Applied Ecological Services’ Taylor Creek Restoration Nurseries (AES)
Hydro-seeding and planting of plugs: Blueville Nursery Inc.

Project Team

Landscape Architect: Jeffrey L. Bruce and Company, Inc. 
Architect (west green roof): Gould Evans Associates 
Architect (east green roof): Ebert Mayo Design Group 
Engineer (west green roof): Bob D. Campbell & Company 
Engineer (east green roof): Orazem & Scalora Engineering
Contractor: Blueville Nursery
Project Oversight: Kansas State University facilities staff
Maintenance: Kansas State University grounds staff
Research and Vegetation Management Support: Kansas State University faculty and students

Role of the Landscape Architect

The landscape architect designed the two green roof systems and oversaw their implementation including oversight of installation of insulation, waterproofing, drainage layer, geoweb matrix, substrates, and vegetation (seeded and then planted); specified nutrients to be added; designed the irrigation/water management system; and helped support Kansas State University (KSU) faculty and student research on the two green roofs. Working with KSU faculty and students, the landscape architect continues ongoing landscape performance monitoring for the green roofs and soil systems.