There are few buildings and homes being built in Portland, Ore., today that aren't green in some way. But for the city's planners, the goal isn’t merely reaching a certain number of sustainably built structures--it's about creating a green city, as shown by the recent designation of a handful of urban areas as “eco-districts.”

In the eco-district concept, buildings, streetscapes, landscaping, and infrastructure work together to cut greenhouse gases, reduce waste, and improve energy and water efficiency--much like HVAC, framing, insulation, windows, and appliances combine to achieve energy efficiency at the house level.

“Fundamentally, it’s the next generation of green building strategy,” explained Rob Bennett, executive director of the Portland + Oregon Sustainability Institute, a nonprofit entity created this year to engage government officials, academics, developers, and builders in the formation of a series of eco-district pilots. “We are taking what we’ve learned from green building and applying it at a neighborhood scale.”

The approach connects with Portland's Climate Action Plan, which seeks to reduce the city's greenhouse gas emissions by 80% by 2050. Within that framework, the eco-district initiative will test concepts of passive building design, equipment efficiency, citizen behavior (car and bike sharing, recycling, and habitat conservation), district-scale renewable energy production, and water conservation and reuse.

One such strategy will involve centralized heating and cooling systems that promote “energy balancing” across multiple buildings, explains architect and urban planner Eric Ridenour. Ridenor's firm SERA Architects is under contract to develop a pilot plan for Portland State University and its surrounding neighborhoods.

Under an energy-balancing plan, heat-producing buildings (like those with multiple server rooms or cafeterias) could feed heat-seeking buildings (such as residence halls or offices) through a district-wide thermal transfer loop system, thus eliminating or reducing the need for larger boiler capacity in individual buildings. Ridenour says St. Paul, Minn., has explored similar large-scale methods for sharing heat among buildings.

But the eco-district concept is not always automatically embraced; proposed efforts in Seattle to create "climate benefit districts" have thus far failed to achieve adequate funding support.

Portland's urban revitalization projects will strive for what Ridenour calls “hydrological equity” by capturing and redistributing rainwater across the eco-district. Once a certain amount of water is returned to rivers and streams, the extra water may be integrated into plumbing systems as non-potable water. Graywater solutions and systems may also emerge. For example, a apartment building or recreation facility with a large shower or laundry load could end up providing water for the toilets of an adjacent office building.

“There are limits to what you can do at the building scale,” Ridenour observes. “Eco-districts look at things in a broader, more systematic way. This is a perfect opportunity to reinvent infrastructure to serve green building goals beyond the scope of a single building.”

At present, four pilot plans are in development for Portland’s university, Lloyd, and south waterfront districts; and Lentz and Gateway neighborhoods, with development expected to begin in 2012. Bennett is hopeful that the effort will not only reduce the city’s environmental impact, but help grow its green job base, expand its roster of clean-tech corporations, attract outside investment, and extend what is fast becoming one of its number one exports.

“At the heart of this is an economic development strategy,” Bennett says. “Portland is an innovative sandbox, and a lot of our green building firms go on and get work all over the globe based on their work here.”

Jenny Sullivan is a senior editor covering design and community planning for BUILDER.