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Environment and Natural Resources 2 Building (ENR2)

Landscape Performance Benefits


  • Reduces runoff for a 2-year, 24-hour storm by 55% as compared to pre-project conditions, with the ability to store up to 31,951 gallons of stormwater on-site per month.
  • Reduces potable water use for irrigation by 100% and total water use for irrigation by 51% with installed irrigation systems that use captured rainwater, condensate, and municipally supplied non-potable water.
  • Reduces volume of air-conditioned space on-site by 24% compared to conventional building practices through open-air “hallway” terraces.
  • Maintains interior courtyard temperatures that are up to 17°F cooler than building exterior temperatures while mitigating urban heat island in 59% of hardscape surfaces with open-grid pavement systems and shading.


  • Provides a satisfying outdoor experience according to 85% of 76 surveyed users, with 95% of regular users reporting that ENR2 and its landscape have a positive impact on their health and well-being.
  • Provides aesthetic value, with 94% of 75 surveyed users rating ENR2’s aesthetic value higher than other buildings on campus.

At a Glance

  • Designer

    Colwell Shelor Landscape Architecture

  • Project Type


  • Former Land Use


  • Location

    1064 Lowell St
    Tuscon, Arizona 85719
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  • Climate Zone

    Hot desert

  • Size

    3 acres

  • Budget

    $75 million

  • Completion Date


Situated on the south edge of the University of Arizona’s Tucson, Arizona campus, the Environment and Natural Resources 2 Building (ENR2) replicates natural sequences and systems to address complex environmental issues. The five-story building centers around a slot canyon form, an ode to the region’s iconic landscapes. Transformed from a campus parking lot with a goal to create a living model of holistic sustainability, the LEED Platinum-certified building confronts the Desert Southwest’s growing climate risks of extreme heat, high winds, long droughts, and intense rainfall. A vertical ecosystem of native and native-adapted flora and fauna spans all floors, living exclusively off stormwater runoff, captured building condensate, and reclaimed water. The structure and landscape work together to minimize the impacts of summer heat, reducing the building’s energy costs and allowing the outdoor spaces to be comfortably shaded microclimates year-round. As a research, administration, and instruction building, ENR2 represents the integration of human and natural systems to achieve a high-performing landscape.

  • Manage 100% of stormwater for a 100-year storm event and capture 90% of average annual rainfall runoff.
  • Use harvested and reclaimed water for all non-potable uses.
  • Create microclimates on site to provide comfortable outdoor spaces for students.
  • Create flexible spaces as social amenities for students.
  • Reduce student stress levels.
  • Create an educational living laboratory that supports and showcases the University and departments’ sustainability mission.
  • Create pollinator species habitat with native plants.
  • Modeled after a slot canyon, the central outdoor courtyard creates an exterior air circulation effect, driving down internal building temperatures. It features 4,773 sf of shaded outdoor seating and study areas across 6 floor levels adjacent to classrooms and offices.
  • 19,829 sf of green roof and planting areas are integrated into the architecture on over-structure decks on each floor with native and adapted plants such as purple heart (Tradescantia pallida), sage (Salvia spp.), agave, and jacaranda (Jacaranda mimosifolia), which were selected for drought tolerance and appropriateness to available light levels.
  • A 5-story water harvesting system with multilevel planting areas, visible downspouts, and a 52,600-gallon underground holding and filtration tank capture 260,000 gallons of rainwater runoff annually for irrigation use.
  • The building and landscape hosts on average 1,500-2,000 visitors per week and serves as a campus landmark and primary meeting place for introducing local and international delegates to campus sustainability efforts.
  • The 151,000-sf LEED Platinum-certified building is constructed with low-maintenance, durable building materials designed to last 100 years. Sustainable architectural features include an outdoor air system, induction coils, and active chilled beams that integrate and work with the landscape systems to efficiently heat, cool, and ventilate the building.

The landscape design at ENR2, in conjunction with the architectural forms, mimics and perpetuates the natural forms and climatic sequences of a slot canyon with its narrow drainageway and sheer rock walls. The design team studied forms and features across Arizona canyons and abstracted key features to fit the building program with an interior courtyard that serves as a microclimatic refuge in an otherwise hot and dry desert environment. Parallel design features include:

  • Hanging plants suspended from the canyon walls provide a lushness that follows the habits and patterns of water and creates a soft contrast against the angular backdrop of the walls.
  • Light from the intense desert sun bounces between the walls with manifestations of light and shadow that softens within the depths of the canyon and changes through daily and seasonal cycles.
  • Forms and patterns are mimicked in the rock formations and wall forms referencing the seasonal changes within desert canyons going from wet to dry and in face of the erosive forces of the wind and water.
  • Open stormwater drainage columns spanning from floor to ceiling across the six stories reveal themselves during the monsoon rains and reflect the sudden changes that can occur in desert canyons as water finds its way across the parched landscape.
  • An interpretation of a tinaja, or pool of water in the stone within desert canyons, marks the bottom of the canyon as a subtle focal feature against the lush vegetation and forms on the ground level.

The interior courtyard with the over-deck gardens on each floor is a key element in creating the canyon effect of the building and landscape. While estimated to cost an additional $425,000 as compared to a conventional, enclosed building, the over-deck gardens offer significant value through an array of environmental and social benefits including habitat creation, microclimate, biophilic benefits, reduced energy costs, and architectural recognition and acclaim for blurring the line between building and landscape.

  • Earlier coordination between the landscape architect and architect during the schematic design phase would have strengthened the interaction between the building and landscape to provide more light for the planting areas in the internal courtyards.  The low light levels made it challenging to use purely native plants. It became necessary to add non-native, shade tolerant plants to the plant palette, and in the deepest areas, shingled stone was used as an aesthetic substitute for plant materials, drawing from the design inspiration of the slot canyon landscape.
  • In the early planning stages, architectural plans provided structural support based on 6- to 8-in depths of soil on the over-structure decks. An increase in depth was not possible because it would require a more substantial structural system and increase project costs. Therefore, planting plans had to tailor to beds with less soil. Where possible, berms were created to provide greater planting depths within the space provided.
  • Some of the terraced planting areas do not receive rainwater from above and are irrigated with reclaimed water and harvested water that includes water that leaches through the planting soil.  This resulted in a higher level of salinity in the water sources being applied for irrigation. Efforts were made to select plants that are suited to handling higher levels of salinity.  It is unclear how broadly this has affected the plants, but it is heavily suspected that it had an impact on the vitality of the plant material as water tests show elevated salinity levels.
  • Applications of stabilized decomposed granite placed on the over-structure deck failed due to the movement of the structure when detailed similarly to ground surface applications.

Aggregate Surfacing / Decomposed Granite: Kalamazoo Materials
Stabilizer: Gail Materials
Decorative Rocks: Anasazi Stone Company
Concrete Paving & Asphalt Materials: Cal Portland
Water Harvesting Tank: Duramax
Stormwater Filtration System: Contech Engineered Solutions - VortSentry® HS
Irrigation System: Rain Bird, Cresline-West, Calsense, Pacific Plastics, Spears, Netafim, Oldcastle Enclosure Solutions
Plants: Various nurseries

Project Team

Landscape Design Architect: Colwell Shelor Landscape Architecture
Landscape Architect of Record: McGann & Associates
Architect of Record: GLHN Architects & Engineers
Design Architect: Richärd Kennedy Architects
General Contractor: Hensel Phelps Construction Co.
Landscape Contractor: Santa Rita Landscaping
Structural Engineer: Turner Structural Engineering

Role of the Landscape Architect

The landscape architect was responsible for the overall hardscape and landscape design of the project, including landscape construction documents. They also developed and documented plant materials research using test plots for selecting an appropriate plant palette that could handle the various levels of shade from the building structure.


Stormwater management, Water conservation, Energy use, Temperature & urban heat island, Recreational & social value, Health & well-being, Scenic quality & views, Shade structure, Rainwater harvesting, Bioretention, Native plants, High-albedo materials, Learning landscapes, Resilience

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