Ann Arbor Municipal Center

Challenge

The client and designers for this project sought to obtain LEED Gold certification: an aspirational, self-imposed goal intended as a demonstration of the City’s leadership in sustainable practices and policies. Because over 50% of the exisiting site was impervious, the design would need to achieve a 25% decrease in the volume of stormwater runoff from the 2-year, 24-hour design storm in order to meet the LEED-NC Sustainable Site Credit 6.1: Stormwater Design: Quantity Control.

Solution

The design team integrated a variety of layered surfaces and materials—using both building and landscape features—to manage water on-site. The stormwater system included multiple strategies for collection, holding, evapo-transpiration, detention, and infiltration, resulting in a drastic reduction in stormwater runoff. Water held on-site is also circulated through a prominently displayed fountain sculpture, designed to engage spectators with the stormwater management system.

• The site offers seasonal public access to a green roof promenade and picnic tables above the first level of the Larcom Building. The green roof features over 5,000 vegetated trays (two square feet each), each planted with a variety of sedum, scattered with alium (wild onion) for color and height. The trays cover 10,318 sf and provide 3,436 cubic ft of soil volume, thus helping to retain water and reduce the potential for the roof surface to heat up.
• Stormwater from the south side of the building is retained on-site in a 15,000-gallon cistern where it is used for on-site irrigation. This water is also used to animate the bronze-clad fountain sculpture that is the focal point of the south plaza near the entrances to CIty Hall and the Justice Center.
• An open-grid pedestrian bridge crosses the cistern allowing water to pass through the bridge to 2,443 sf of rain garden area below.
• The 5,280-sf street-level south plaza is covered with permeable unit pavers, allowing stormwater to infiltrate into the underlying subgrade.
• The vehicular parking area on the north side of the site is surfaced with 12,326 sf of interlocking concrete permeable paving units. A granular subbase under the pavement is used as temporary storage for infiltration and detention of stormwater from the north half of the Larcom Building.
• The west portion of the court and police building drains into 1,408 sf of rain gardens between the public sidewalk and the building. The rain gardens cover 14 gravel columns, or drywells, increasing the amount of infiltration.
• 32 native and non-native plant species were installed, including hardy trees, shrubs, vines, forbs and grasses that can withstand the harsh urban environment.
• Building exterior walls are designed to display framed works of art that are easily visible from street level walkways.

• The permeable unit pavers installed in the vehicle parking area north of the Larcom Building save an estimated $7,429, or 16% compared to the cost of a conventional concrete pavement over a 30-year service life cycle.

• As originally designed, the rain water available from the on-site cistern was not adequate to recharge the fountain sculpture, due to higher than expected evaporation rates from the bronze surface of the sculpture. As a result, the fountain needed to be augmented with fresh water. This runs counter to the design intent.
• The selection of a prominent nonlocal designer to design a fountain sculpture drew significant criticism from the public and the local arts community. The client might have been better served by using an open, competitive selection process. Involving the artist earlier in the design process would also have allowed artist input into the location of the sculpture and thus better integration into the landscape and building rainwater management system.
• Slight color shifts are noticeable in the permeable parking area. To ensure a more homogeneous appearance in color, pavers should be mixed from multiple pallets during installation.

Project Team

Client: City of Ann Arbor
Architecture: Quinn Evans Architects
Landscape Architect: Conservation Design Forum (now Environmental Consulting & Technology, Inc.)
Landscape Architect: InSite Design Studio
Waterscape: Atelier Dreiseitl
General Contractor: Clark Construction Company

Role of the Landscape Architect

The project was directed by an architecture firm with local expertise in green building, with two landscape architecture firms charged with designing the rainwater capture and recycling systems. The design process required close collaboration between team members to thoroughly integrate site and building systems. The landscape architects communicated directly with the contractor during construction in order to maintain design intent.