As green roofs proliferate atop new buildings in Portland, landscape architects are learning lessons about what works and what doesn’t.

In July 2020, the Portland City Council adopted the Central City 2035 plan. Among sweeping changes to the zoning code, new rules require eco-roofs atop buildings of 20,000 square feet or more in commercial zones within the Central City.

Eco-roofs aren’t exactly new, but their widespread adoption is. The city required its own large-scale buildings to have eco-roofs beginning in 2015.

The rooftop gardens are also called green roofs, but the city of Portland uses the term “ecoroofs.” They have many benefits, according to boosters, but also some costs.

Foremost among the benefits is stormwater management. Eco-roofs filter stormwater and keep it from reaching waterways, particularly the Willamette River.

Eco-roofs also reduce the urban heat island effect, in which a city’s built surfaces absorb heat and raise temperatures in the area.

Eco-roof-like features can be an aesthetically pleasing amenity for residents, as at the Mirabella building in the South Waterfront. There, they appear on terraces.

For developers and project owners pursuing Leadership in Energy and Environmental Design and similar certifications, eco-roofs are often awarded hefty point totals.

Increasingly, eco-roofs are also a steady stream of revenue for landscape architecture firms.

“We are seeing an uptick in it,” said Jeramie Shane, a Mayer/Reed principal who designs eco-roofs. Other landscape architecture firms including PLACE, which is responsible for designing the eco-roofs on the Block 216 tower, and Lango Hansen, which designed a prominent eco-roof for Hyatt Unbound, have benefited from the wider adoption of eco-roofs.

A study by Reed College researchers identified 384 eco-roofs in Portland as of 2019; they totaled nearly 1.4 million square feet.

As new buildings rise in coming years, central Portland from the air will increasingly look like a series of small green spaces. Densely packed districts with eco-roofs will encourage pollinators to flit from rooftop to rooftop.

Green roofs, Shane said, “create and maintain habitat districts. We see the connectivity of green roofs being really vital to provide habitat.”

Shane recalled that he recently visited Oregon Health & Science University’s Knight Cancer Institute when a hummingbird appeared.

Among the issues landscape architects have discovered is that solar panels compete with greenery for rooftop space.

“(Photovoltaic) panels want to occupy the same space as the green roof does,” Shane said. “We’ve been testing planting green roofs under them, and in some cases they’ve been successful.”

Techniques such as planting shade-tolerant plants have helped. Landscape architects also tend to favor drought-resistant plants that can make it through Portland’s dry summers. “Right plant, right place” is a goal for successful eco-roofs at Mayer/Reed, Shane said. Often, on rooftops exposed to sun and wind, that means sedum and other succulents.

“Generally, the summer months tend to be gaps” in rainfall, Shane said. “That’s one challenge that we’re always trying to build some resiliency toward.”

Eco-roofs can be “intensive” – marked by deeper soil and greater plant variety, or “extensive” – tending to be wider but with shallower soil. Extensive eco-roofs seldom have irrigation, but intensive installations sometimes do.

“The intensive ones, we can get more creative, because we’ll use irrigation on them,” Shane said. “We can get rich, robust landscapes out of them.”

It can also be tough on buildings with smaller footprints to provide an eco-roof of a meaningful size, Shane said.

Eco-roofs do require ongoing maintenance that adds cost to any project. That makes it best for a building owner that is willing to put in greater costs up front, and in the long run, for a major building amenity.

“The developer has to acknowledge the benefits for a longer investment,” Shane said.

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The city of Gladstone is preparing to welcome one new building, with two distinct uses.

General contractor P&C Construction is wrapping up work on the Gladstone Civic Center, which will house both the police department and city hall. Punch list items are being tackled, and substantial completion is expected later this month.

Scott | Edwards Architecture designed the building. Ground was broken in April 2019.

“We really worked closely with the chief of police and the city administrator early on to develop how this site shook out, so to speak,” said Jennifer Marsicek, a senior associate with Scott | Edwards Architecture. “It actually works pretty well to have the police side separate from city hall because of the seismic and the resiliency measures the police side requires that the city hall side doesn’t require. And joining it with a mass-timber lobby really made sense overall.”

The single-story building has slightly fewer than 20,900 square feet – around 13,000 square feet on the law enforcement side. That part of the building is built to Category 4 seismic resilience, while the city hall portion is built to Category 2 resilience. This is in part because the police headquarters also will serve as a city emergency operations center.

The city hall side will house administration, planning and other key departments, as well as a city council chambers that will be able to serve as a municipal court.

The two sides are joined by a gently tapered corridor topped with exposed cross-laminated timber panels and glulam columns and beams. Historic photos of Gladstone adorn the corridor walls next to public-facing department entrances.

“With the separation we were basically able to build two separate buildings and do the infill with CLT,” said Will Somme, project manager for P&C Construction.

The two-acre site sits next to the city’s public works facilities and across the street from Gladstone High School. The new complex also will provide additional off-street parking.

Unlike Oregon City’s Robert Libke Public Safety Building, which features CLT wall and ceiling panels, the Gladstone Civic Center has only CLT ceiling panels.

“This is concrete tilt on both sides and you have a wood diaphragm group, whereas out there it’s all CLT and you have all the extra bracing,” Somme said. “You don’t have to go to that extent when you have a concrete tilt structure.”

The Gladstone building’s police side has a backup power generator and water, as well as gas service separate from the civic side.

“The diaphragm still was a lot of work, specifically on this side, where you saw there’s a break where it goes from a Category 2 to a Category 4 building,” Somme said. “There’s a full seismic joint that runs through the interior of the lobby, so you have that flexibility there.”

Combining practical police needs with more aesthetic civic ones can be a challenge for designers, and Marsicek worked with Lango Hansen Landscape Architects to provide the city with a warm public space filled with plants. Glulam beams even extend outside the building and provide support for planters that will eventually sport fresh vines.

“It was their concept,” Marsicek said. “And with an overall site design that drains into a central swale it made sense to bring that into the building.”

The project was one of the first in Oregon to come together via progressive design-build delivery. In this method the owner retains a design firm and a construction firm early on for joint work on planning, design and construction – with agreement on price and schedule. The method can shorten project schedules, including procurement, and create a single point of responsibility for owners.

“It was a new experience for us,” Marsicek said. “It was really a team effort from the beginning with P&C, the owner and us.”

The method made sense for this particular project, Somme said.

“Contracted police buildings are unusual, and that’s why you typically see a different delivery method based on qualifications,” he said. “Because you just don’t want a contractor to come in, and nothing against them, but to not have that experience, because of what goes into these buildings, it usually doesn’t work.”

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Work is about to commence in Northwest Portland on the Field Office project, a uniquely-designed mixed-use project with a hefty office component.

Developed by sustainable specialists project^, Field Office consists of two buildings 6 stories each, approximately 290,000 square feet total, with one level of underground parking. The project was designed by the firm of Hacker  and landscape architect Lango Hansen to be a retail and work space that “blurs the lines” between indoor and outdoor architecture, with a campus environment in an urban setting, and landscaping pervasive at all levels of the buildings, according to project^ principal Jonathan Ledesma.

The general contractor is Lease Crutcher Lewis. Work is expected to conclude in the third quarter of 2017.

The owner is National Real Estate Advisors. KPFF is the structural engineer and Humber Design Group is the civil. Office leasing is being managed by Jones Lang LaSalle and retail leasing by Urban Works.

The project^ team declined to disclose the project price.

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