Project DescriptionAfter two years of struggle, a Portland, Ore.-based developer was forced to concede that good intentions do not always produce good results. A firm known for its commitment to environmental issues, Gerding Edlen Development decided to build an eco roof as part of its Brewery Blocks project, a development at the former site of the Blitz-Weinhard Brewery in Portland’s Pearl District. The mixed-use project includes approximately 1.7 million square feet (157930 m2) of urban retail, Class A office space, housing units and parking.
“We had five city blocks, comprised of a series of brewhouses, warehouses and some buildings that were specifically designed around beer storage,” says Dennis Wilde, partner at Gerding Edlen Development. “A couple of those buildings were historic landmarks, so we retained those. The rest were so specific in their design that they really weren’t adaptive, so they came down.”
Today, the development is made up of six buildings, each carrying a LEED certification from the Washington, D.C.-based U.S. Green Building Council. One is rated Silver, four are rated Gold and one carries a Platinum certification.
The green strategy for the project included a vegetated roof on the LEED Gold-rated “Block 4”, later named the M Financial Building. In spite of careful planning and research, the original eco roof never lived up to expectations. “Frankly, we had never done a vegetated roof before, nor had our landscape architect, nor had our contractor,” Wilde says. “Between the three of us, we managed to screw up pretty much everything.”
GOT THE LOOK
Work on the M Financial Building’s vegetated roof began in 2003. It was to be placed on a 2-story podium element and the initial goals were primarily aesthetic. “We were interested in doing some green roofs for a variety of reasons: the insulative qualities, reducing the heat-island effect and reducing storm-water runoff,” Wilde explains. “But what convinced us from a business perspective was the fact that we had buildings all around looking down on that roof.”
Another motivator came from local incentive programs. “The city of Portland has floor-area-ratio bonuses for eco roofs,” says Renee Worme, LEED AP and sustainability manager at Gerding Edlen Development. “It’s nice when policies support sustainable solutions and reward buildings for doing something that’s good for the environment.” Taking advantage of this density benefit meant the green roof would translate into additional space throughout the development.
At the time, few if any eco roofs had been constructed in Portland, so the design team Gerding Edlen Development assembled was working from scratch. Little information was available about creating a successful vegetated roof in that climate. “It was a new idea and we weren’t sure how to approach it,” says Chris Wayburn, AIA, LEED AP, an architect with Portland-based GBD Architects, the designer of the M Financial Building. “We had all sorts of grand ideas of occupied terraces and patios, but because of code issues and real-world concerns, those eventually went away.”
The goal shifted to make the roof a visual amenity. “We had some technical issues with how deep we could make the roof,” Wayburn says. “We started looking at a thinner eco roof. It would be something that would have sedums and other similar plantings. At the time, we thought that was all you could do with a thin-profile eco roof.”
DOWN THE DRAIN
Trouble came in three major areas: drainage, plant selection and soil. The drainage issue was the first to emerge, making itself known almost
immediately. “Conventional wisdom was that one of the benefits of an eco roof is that you don’t need to slope and drain it,” Wayburn recalls. “We thought it could be a flat roof because it was designed to retain water and doesn’t need to drain as quickly as other roofs.”
Unfortunately, this approach didn’t work as expected. “We had some ponding water because the roof was very flat,” Wilde admits. “We didn’t have enough drainage to compensate for the water ponding, so some areas of the roof stayed perennially wet. The plant community we selected couldn’t tolerate that.”
A flat roof does offer construction-cost savings over a sloped roof, which was an incentive in this case. However, a flat roof isn’t always entirely flat. “What we found was that, with a post-tensioned concrete deck like the one we had, there are natural highs and lows in the concrete as it warps with the tensioning of the tendons that make up the post tensioning,” Wayburn explains. “We were finding valleys between the beams. We had low points and high points that were not corresponding to the drains.”
Drains were flush or higher than the low points of the concrete slab, so the water had nowhere to go. The team also had decided on a thin drain mat, which added to the problem. A few quick fixes were attempted, such as using foam insulation to build up the low points and get the roots of the plants out of the standing water, but ultimately the problem persisted.
YOUR SOIL HIGHNESS
When the project began, many of the advancements in vegetated roofs were taking place in Europe. Consequently, the project used European plants rather than local species. “The planning was taking place in 2002 and nobody in Portland knew much about eco roofs,” says Wilde. “We were looking at what had happened in Europe, so a lot of the sedums were coming from Germany. Oregon has very wet winters and very dry summers, so the plants we selected couldn’t tolerate those wild swings.”
The result was a vegetated roof that struggled with the seasons. “The only things that really grew were the mosses and windblown seeds that landed on the roof,” Wilde recalls. “So there would be this green mass during the winter from the moss that was able to tolerate the conditions, then it would be bone dry and look terrible all summer.”
A temporary irrigation system was installed for use in the summer, but LEED requirements allow a potable-water irrigation system to be used only for two years and no rainwater capture system had been installed on the building.
Kathy Bash, LEED AP, formerly with GBD Architects and currently with Portland-based BMS Architects, has studied numerous vegetated-roof installations. She conducted an analysis of the failure of the M Financial Building’s eco roof in 2004. “What’s pretty surprising to most people is that, even 40 feet [12 m] above the sidewalk you have a different microclimate than you do at street level,” she says. “Eco-roof plantings are different than those on the ground.”
Adding to this perfect storm was a soil mix that had far too much organic content for the plants selected. “Back then, everyone was saying you had to go with high organics,” Wayburn says. “The soil just clumped up and went nasty on us. The plant design was poorly balanced for the application.”
“If you’re planting sedums and other drought-tolerant plants, you find they normally grow on rock faces and in crevices where there is virtually no soil,” Wilde explains. “These plants don’t like rich-humus soils. They like soil with good drainage, high-sand content and very-low-organic content. So we were putting these very-rich, organic soils on the roof and drowning the poor plants.”
“When the M Financial Building’s eco roof was done, it had less organic material in the mix than anyone at the time thought plants could survive in,” says Bash. “They really thought they were pushing the limit of using inorganic material. What’s curious is that they needed to use even more inorganic material, rather than less.”
TRY AND TRY AGAIN
In the face of the drainage, plant and soil problems, Gerding Edlen Development tried a number of temporary fixes to salvage the eco roof. “We did some replanting, pretty much sticking with the original palette of plant materials. We did some plant augmentation and added some new plants to see if we just hadn’t been generous enough with the original planting,” Wilde recalls. “None of these efforts were particularly beneficial.”
Still, the firm was not ready to abandon the eco roof. In 2005, Gerding Edlen Development started over. “We hired a local horticulturist who really understood native plants and had a good understanding of what would survive in this environment,” Wilde says. “He worked with a small landscape architecture firm to develop a strategy and a new soil mix. We went back to square one and redesigned the whole system.”
Today, the second vegetated roof on the M Financial Building is performing beautifully and is, at last, something the team can be proud of. An improved drainage system and more regionally appropriate plants and soil mix are a big part of its success. “It’s working fabulously now,” Wilde says. “The difference between looking out there now and looking out there two years ago is night and day.”
Winston Churchill once said, “Success is not final, failure is not fatal, it is the courage to continue that counts.” Gerding Edlen Development had the courage to continue and ultimately ended up with a successful vegetated roof, as well as a number of valuable lessons for future projects. “Lesson number one is to make sure that your landscape architect has successful experience with vegetated roofs because they can be problematic if you’re not careful,” Wilde says. “Number two is to develop a deep understanding of the drainage, soil and plant issues you need to have a successful installation.”
“Gerding Edlen Development was on the leading edge and everyone on the team was learning as they went along,” Bash says. The general body of eco-roof knowledge improved during the construction process and that’s what’s so great. The construction community’s understanding of eco roofs is moving forward to the point where they can be more successful.”