Phipps Conservatory Center for Sustainable Landscapes

Challenge

The first major design challenge faced in the project was managing the steep slopes on the existing site. The design had to balance slope stabilization with accessible visitor circulation and stormwater management features. The other major challenge was confronting visitors’ expectations for an ornamental conservatory garden aesthetic with non-traditional native plant communities on a limited landscape budget.

Solution

The design addresses steep slopes through the use of seed mixes and plant communities native to those conditions, and by regrading to create terraces and an ADA-accessible path that descends diagonally across the slope. The significant grade changes and circulation pattern are used to let the landscape narrative unfold for visitors and introduce them to a sequence of native plant communities. Upland and dry plant communities are incorporated into the higher areas of the site, while the lower portions feature wet and lowland plant communities and stormwater management features. The limited landscape budget led to the extensive use of seed mixes throughout the site, resulting in a landscape that is designed to grow in over time rather than offering an immediate appearance of particular mature plant communities.

• A range of water management features, including a green roof, cistern, underground storage basins, a lagoon, constructed wetlands, subsurface sand filters, UV disinfection system, rain gardens and pervious asphalt parking lot manage all building wastewater and stormwater on site.
• Building wastewater is collected in a 1,000-gallon septic tank, released 50 gallons at a time into two 180-sf horizontal subsurface flow treatment wetlands, recirculated through a below-grade sand filter, conveyed to a UV disinfection system in the building, and then stored in a 1,700-gallon cistern for reuse within the building for toilet flushing. Excess treated water that is not needed in the building is pumped to UV/filtration systems located elsewhere on the conservatory grounds and is either distilled and used for irrigation within the Conservatory’s Orchid Room or infiltrated into the ground.
• The 4,000-sf lagoon captures cistern overflow as well as on-site stormwater for storage and treatment. Overflow from the lagoon is diverted to parking lot rain gardens for infiltration.
• 3 rain gardens capture water from the staff parking lot, the service drive, and the meadow slope on the west side of the building.
• A below-grade crate storage system with a total system capacity of 80,000 gallons includes a 20,000-gallon unlined overflow area, which allows excess water to infiltrate naturally as needed.
• Two 1,700-gallon cisterns store stormwater runoff from the roof of the new Center for Sustainable Landscapes building as well as adjacent existing conservatory buildings. The cistern water is reused for building and irrigation needs.
• The 6,050-sf green roof is planted with over 30 species native to within 200 miles of the site. Species were selected for their permaculture traits and history of medicinal, biofuel, or culinary usage.
• Monitoring stations in the rain gardens and on the green roof collect data on rainfall, water quality, water storage in soil, water level in rain gardens, and green roof drainage.
• Areas of the site with steep slopes use specially engineered geofiber-reinforced soil mixtures.
• The site planting palette represents 9 different plant communities- cultural/ornamental gardens, rain gardens, wetlands, evergreen woodland, lowland slope, water’s edge, successional slopes, upland oak woodland, and upland grove. The 150 native plant species added to the site improve habitat quality and include red maple (Acer rubrum), eastern redbud (Cercis canadensis), green hawthorn (Crataegus viridis), fragrant sumac (Rhus aromatica), blue flag (Iris versicolor), mountain laurel (Kalmia latifolia), butterfly weed (Asclepias tuberosa), tall coneflower (Rudbeckia laciniata), riverbank grape (Vitis riparia), and golden Alexander (Zizia aurea). 
• The site serves as a demonstration landscape, with interpretive signage to identify plant species and performative aspects of the lagoon, constructed wetlands and rain garden.

The native plants at the Phipps Conservatory Center for Sustainable Landscapes grounds cost $0.80 per sf to maintain, as compared to $1.01 per sf, a 20% savings. 

• The Living Building Challenge certification required that all materials be procured locally. This caused a number of design challenges and required flexibility on the part of the design team. For example, the quartz-derived sand originally specified for subgrade fill was prohibitively expensive due to demand from the local hydrofracking industry. This resulted in the substitution of a limestone-derived sand. The more alkaline soils that resulted from this substitution necessitated a substantial revision of plant species, to ensure that specified plants could thrive in higher pH soils.
• Construction scheduling and sequencing proved crucial to some of the performative aspects of the landscape. For example, the subsurface treatment wetlands were initially installed in the fall. At the time, they did not meet regulatory requirements for biological oxygen demand (BOD), which is highly dependent on water temperature. The wetlands met the requirements in the spring after warm weather. If the wetlands had been constructed in spring instead of fall, they would have likely met regulations when they were first installed.
• The sanitary water management system was designed to reuse treated water in the building for toilet flushing after passing it through subsurface treatment wetlands, a sand filter, and UV disinfection. The system is designed to receive 416 gallons per day from the building (243 gallons per day from flush fixtures and 174 gallons per day from flow fixtures). The actual building water use has up to this point been significantly lower than the designed capacity, so captured stormwater is run through the system to keep it flowing at the required rate for operation. Excess treated water that is not required for building demand can be used after UV treatment to offset irrigation needs within the Conservatory’s Orchid Room.

Unit Pavers: Hanover Architectural Products, Inc.
Stone Paving: Raducz Stone Corporation
Path Lighting: Modular International Inc.
Benches: Keystone Ridge Design
Bike Racks: Bike Pittsburgh
Trash Receptacles: United Receptacle, Inc.
Bollards: Keystone Ridge Design

Project Team

Landscape Architect: Andropogon Associates
Architect: The Design Alliance Architects
Civil and Geotechnical Engineering: Civil and Environmental Consultants Inc.
Environmental Engineering: CH2M Hill, Inc.
Structural Engineering: Atlantic Engineering Services
Mechanical, Electrical, Plumbing Engineering: CJL Engineering
Lighting: CJL Engineering
General Contractor: Turner Construction

Role of the Landscape Architect

The landscape architect served as a subconsultant to the architect. As part of the Living Building Challenge, the design process was highly collaborative among all consultants. The landscape architect’s role involved the design of the site’s landscape, hardscape elements, and stormwater and wastewater management systems, along with extensive coordination with project architects and civil engineers.