by Jason King
Building on the previous post, the Bonneville Power Administration Green Roof went through a number of iterations in the design process, and also required the attention and on-site modification that often comes from challenging retrofits.
The existing rooftops during demolition - predominately paved with small planters which made them feel somewhat barren. Pavers were saved and re-used in the final design which saved cost and materials.
Landscape Architect’s Role The project involved working with a diverse group of stakeholders in developing the concept, as well as coordinating with multiple trade partners as part of the design-build collaborative team. The combination of technical knowledge and experience with various green roof projects allowed the team to adapt to unique site conditions while remaining conscious of project goals and overall budget constraints. Working on structure requires knowledge of multiple systems and how they interact. In this case, the GSA outlined specific goals, but left it open to the design team to come up with creative solutions that fit the overall budget. Conversely, on a typical project, we would select a system based on the unique conditions of the project.
In this case, however, the roofing system was predetermined, so it became a challenge to fit a particular system to the project parameters. This, along with integration of additional insulation to meet energy efficiency goals meant that we needed to troubleshoot conflicts between competing project goals, allowing us to maintain safe parapet heights, incorporate window-washing infrastructure, and maintain ADA accessibility at thresholds.
A typical roof level after installation, showing the transformation of the space, with seating areas located in sunny perimeters, vegetation free zones at building edges, and the pattern of bermed vegetations with rock ‘stream’.
Another particular challenge was the structural capacity of the roof. It was determined that we had the ability to berm up in certain areas of the roof, where the original planters were located. Rather than create a homogenized and monotonous pattern, the berming configuration shifts on every roof, but still falls within specific loading parameters – invisible to the naked eye. As with most projects, determining the right mix of plantings was also vital, as the conditions for each rooftop and region vary. In this case, the terraces were on the north side of the building so the conditions were more shady, with early and late sun. Using regional experience with multiple projects and microclimates – the designers developed a palette of plantings that provided diversity, habitat, stormwater management, and heat island mitigation, while providing a dynamic and beautiful amenity for the building users.
- Looking from the west towards the doorway to the interior of the office. The stream winds through a range of colors and textures that include a mix of evergreen and deciduous plantings adapted to rooftop conditions.
HIGHLIGHT: A Model for Energy Efficiency Until now, vegetated roofs have not been considered viable. A recent decision by the Oregon Construction Industry Energy Board, as part of the Reach Code, recognized green roofs as both an energy conservation measure and as way to help reduce urban heat island effect. The BPA project exemplifies the concept of energy efficiency.
View from east access of typical roof, highlighting the dynamic nature of the berms along with the varying textures and colors of semi-intensive plantings. Sedum cuttings quickly colonized the low areas and side slopes to provide erosion control, color, and texture, augmented by herbs and edibles like coast strawberry available at the edge for grazing by building tenants
INNOVATION: Integrated Project Delivery Another unique feature of this project is the delivery of services. There is a trend in the green roof industry towards integrated projects, and the team has responded to this by the creation of a design-build collaborative, including the roofing contractor, landscape contractor and landscape architect as a core team. Additional sub-consultants such as structural, architectural, mechanical and related trades are added to projects on an as-needed basis. The result is a simplified process, combining all of the necessary elements together in a team with proven experience working together on similar projects. Each consultant and contractor maintains a clear distinction in scope that adheres to professional responsibilities, but the process is streamlined with more clarity of communication and documentation. For this unique project the General Contractor (GC) was able to contract with one entity to provide complete design and construction services. The team also brought in structural to evaluate roofing capacity, and mechanical engineering to assist with rainwater harvesting systems.
The variety of colors and textures occupy complex vignettes that display the periodic colors and textures. The bloom of the sedum species, natives perennials with vibrant summer blooms like Oregon Sunshine, and the pink tufts of drought tolerant Armeria maritima play off the more subtle purple shades of Hidcote Lavender.
PROJECT SUMMARY
Project Name:
Bonneville Power Administration (BPA) 905 Building Green Roof Terraces
Landscape Architect:
TERRA.fluxus | Landscape + Urbanism (Portland, OR)
Client:
General Services Administration (GSA) building owner
Bonneville Power Administration (BPA) building tenant
General Contractor:
Allen Bradbury Construction (Auburn, WA)
Roofing Contractor:
Snyder Roofing of Oregon (Tigard, OR)
Landscape Contractor:
Teufel Landscape (Portland, OR)
Mechanical / Plumbing Design (Cisterns):
PAE Consulting Engineers (Portland, OR)
