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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In the early returns for Portland’s eco-roofs standard, following the rule is the exception.

Of four Central City projects subject to the city’s eco-roofs rules since the standard took effect in July 2018, only one has met the standard. One was approved by the Portland Design Commission with a much smaller eco-roof atop the podium, and requests for significant modifications of the rule are being made for two others.

In baseball, hitting 1-for-4 is about league average. In city planning, it could be an early warning sign that the rule is either infeasible, or that the city is unwilling or unable to enforce it via the design review process.

“I think it’s a concern for the city,” said Benjamin Nielsen, a senior planner for the Bureau of Development Services. “Developers are having a hard time with some of the requirements of the standard, particularly when solar panels are involved.”

So far, the only project to meet the city’s eco-roofs standard comes from the city of Portland and three partners. The seven-story Fourth and Montgomery project, also known as the Jasmine Block, is under construction in south downtown with an eco-roof that meets the city’s rules. The project will provide space for the city, Portland State University,��Oregon Health & Science University�����Ի���Portland Community College. SRG Partnership designed the building, and Mayer/Reed is the landscape architect. The roof includes solar panels.

The eco-roofs standard took effect last summer as part of the Central City 2035 Plan. Incorporated into Title 33 of city code, the standard requires eco-roofs on new Central City buildings of 20,000 square feet of net area or more within certain zoning.

Eco-roofs are intended to convey several benefits. They reduce urban heat islands, manage stormwater, improve air quality and provide habitat for birds, pollinators and plants.

To meet the standard, at least 60 percent of the roof area must be devoted to eco-roof features, as defined by the Bureau of Environmental Services. The remainder may be occupied by mechanical equipment, solar panels, wind turbines and other items.

Portland’s eco-roofs standard was modeled after Toronto’s, said Mindy Brooks, a city planner with the Bureau of Planning and Sustainability.

Portland’s standard has roots in an earlier, voluntary program. Developers could earn bonus height in exchange for eco-roofs. The Central City 2035 Plan rolled back that bonus, among others, in favor of concentrating on affordable housing incentives. Eco-roofs were made mandatory.

The trend of project teams requesting modifications for eco-roofs bears watching, Brooks said.

“I think we need to continue to monitor it and see how it goes,” she said. “We’ve had a couple of very unique (projects) be the first ones out of the gate. So it’ll be important to monitor and see how it proceeds.”

Architects and developers have approached the standard in different ways.

At Block 216, the Design Commission agreed to a modification that places the eco-roof atop only the terraced podium, and not the 35-story tower. The Block 216 eco-roof will cover only 33 percent of the roof area, far below the 60 percent minimum.

GBD Architects is designing the project. Before the Design Commission, architects from GBD argued the wind forces at the tower’s 460-foot height would make an eco-roof unworkable and perhaps unsafe, with the potential for soils and plants to be blown afar. Two design commissioners said an exception to the eco-roof standard may be necessary for towers.

GBD did not respond to interview requests.

City officials are researching how eco-roofs can be built atop towers. The bureaus of Planning and Sustainability, Development Services and Environmental Services are looking into how high winds affect tower eco-roofs, and will issue guidance to future project teams.

It may just be a matter of more complex engineering, Brooks said.

“We did some quick research and did not find wind shear at high altitudes being a problem for eco-roofs,” Brooks said. “At high altitudes, engineering becomes more complex, just as anything does at that altitude.”

Brooks said the city wants to get it right before issuing any guidance.

“We heard what (the architects) said and we want to make sure whatever guidance we provide is appropriate,” she said.

Bora Architects is proposing an entirely different solution at Lincoln High School. The project team proposes to meet the standard at ground level, with plantings. The standard would be met with 63,600 square feet of landscaped areas.

At a May design advice meeting, Bora Architects principal Christopher Linn said ground cover performs better as a heat and carbon sink, and requires less maintenance, than an eco-roof.

“I think we have a proposal that better meets the intent of the guidelines than putting planting on the roof,” Linn told the Design Commission. He did not respond to interview requests from the 91��Ƶ.

Some commissioners said they were amenable to the proposed ground-cover solution.

“I’m OK on the (green roof) modification,” Commissioner Sam Rodriguez said. “I believe it is meeting the intent to some extent.”

Brooks, in an interview, said Bora’s approach “could be appropriate” if it goes beyond the minimum standard, and fulfills the stormwater-management and heat-reduction functions.

The team proposing the five-story PAE Living Building at Southwest First Avenue and Pine Street is also seeking a modification to the eco-roofs standard. ZGF Architects is pursuing Living Building Challenge certification, which requires 75 percent roof coverage by solar panels.

“Eco-roof beneath the panels would not be viable, as the required strategy to maximize on-site production necessitates a flat array of panels, without spacing: thus the eco-roof would not get adequate light or rainfall,” ZGF wrote in its application for a modification.

The Historic Landmarks Commission is set to review the PAE Living Building on Monday. The requested modification on the agenda is simply stated: “To not provide the required eco-roof.”

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Columbia Green Technologies opened its doors in Portland about 10 years ago because the city had a reputation for green building and the company’s founders wanted to take advantage. They saw Portland becoming a prime market for their product: vegetated roof systems.

But that didn’t happen, Columbia Green Technologies Chief Operating Officer Greg Love said. Portland is now a minor green roof market, he said, and production here has dropped off.

“We do most of our business outside of Portland,” he said. “Seattle is a big market and now our biggest market is Washington, D.C.”

In 2008, Portland initiated a temporary cash incentive program that triggered a dramatic increase in green roof production. But the $6.5 million program ended in 2012, and production has since decreased and prices have since increased. Now, as the city has shifted financial resources toward affordable housing initiatives, some green roof stakeholders are calling for new incentives.

Matt Burlin, outreach coordinator for sustainable stormwater management for Portland’s Bureau of Environmental Services, reported to the City Council in 2011 that the city’s cash incentive program for green roofs was a success. The city’s list of providers of eco-roofs (the simplest form of green roof), he said in the report, had grown by 30 percent since the program started.

But since 2011, eco-roof prices have risen, said Jon Crumrine, who started Enviroscapes Northwest in response to the city initiating its cash incentive program in 2008. The average cost of installing a green roof now ranges between $12 and $15 per square foot, said Crumrine, who later sold his business to Vaughn Environmental Systems (he was retained as a consultant).

“It certainly didn’t have any impact on (bringing) costs down, but it did help promote the technology in our area,” he said.

Alice Coker, environmental specialist with Portland’s Bureau of Environmental Services, said the city commissioned a that looked into whether the cash incentive lowered prices of green roofs; it was inconclusive.

“We don’t know if it brought prices down,” she said. “There were too many variables involved.”

Meanwhile, the Portland City Council has shifted its emphasis to affordable housing because the homeless population has increased in the past five years, said Ivy Dunlap, landscape architect with the Bureau of Environmental Services.

“Things are so different now, and a different administration has different challenges and there weren’t hundreds of people camped in the Springwater Corridor,” she said.

As priorities change, so do allocations of dollars, according to Troy Doss, senior planner with the Bureau of Planning and Sustainability.

“Because of direction from council, bonuses are shifted to affordable housing,” he said.

That shift in focus has played a significant role in green roof production decreasing here, Love said. For the past five years he has joined Columbia Green Technologies CEO Vanessa Keitges at countless city meetings, he said, to push for more city support for green roofs. Markets like Seattle, Washington, D.C., and Toronto are ripe for green roofs, according to Love, because they offer incentives and rebates for installations.

“Although some jurisdictions will still use incentives (for green roofs), it has become standard practice in a lot of Central City development, and a lot of projects are doing eco-roofs,” Doss said. “And the majority of eco-roofs were not developed using bonuses.”

In addition to the evaporation of the cash incentive program, the proposed draft of the 2035 Central City Plan includes mandates for eco-roofs in certain zones. New buildings with a net area of at least 20,000 square feet would be required to include an eco-roof that covers at least 70 percent of the roof area – with exceptions including HVAC systems and skylights.

That plan has Love’s approval, though he doubts it will become a reality.

“We’ll believe it when we see it,” he said.

Also, the draft plan calls for eliminating a current bonus of floor area ratio (FAR) for providing green roofs.

Architect Shawn Sullivan, eco-roof consultant for Winkler Development, said eliminations of cash incentives and the FAR bonus will increase costs and make developments vulnerable to infeasability.

“It was really nice having the incentive, and I think carrots are always better than sticks,” he said.

Sullivan said he fears the market for green roofs will soften because developers aren’t looking to spend more money.

“If the (incentive) program was here I think we’d be doing a heck of a lot more business,” he said. “With mandates, things are going to cost too much and then we can’t afford to build.”

Wade Lange, regional vice president for American Assets Trust, said the absence of incentives for green roofs could slow development.

“When it adds additional cost without any compensation, it just causes developers to pause and consider whether they want to go forward with the development,” he said.

The city should bring back the cash bonuses or add other incentives for green roofs, according to Greenworks principal Mike Faha.

“I think they should continue or enhance that (cash bonus), given what’s going on around here, that we’re getting denser and denser,” he said. “We know they worked and the city would do better talking to developers about what kind of incentives meet their needs.”

Increasing costs will drive up rents – the opposite of the goal to increase affordable housing, Sullivan said

“Like so many mandates that are good for our city and environment, they (green roofs) increase costs, which have to be reflected in increased rents,” he said. “We currently have an affordable housing crisis, and making construction cost more is not going to be part of the solution.”

However, Amy Chomowicz, the city’s eco-roof program administrator, said there still are benefits to installing green roofs in Portland.

“You can get a reduction on your stormwater bill if you put on (an eco-roof) through the Clean Water Rewards Program,” she said. “There are various ways to manage stormwater on site and if you do an eco-roof over the entire building you don’t have to have ground-level stormwater treatment (for the roof).”

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