Akana recently completed a unique project for Metro, at the Expo Center in North Portland that offers an innovative solution to the common problem of treating and controlling runoff from large roof areas.
Most of us are becoming familiar with “green roofs”, or roofs with vegetative covering, that retain rainwater and allow it to evaporate back into the air instead of overloading municipal sewer and drainage systems. Yet sometimes the location doesn’t offer the room or the structural capacity needed for the additional weight of the green roof. In this case (and for the first time in Portland), the solution is a green wall. Placed against one of the exhibition hall walls, the green wall collects rainwater at the downspout and routes it through a series of troughs supported by steel posts and beams. The troughs are made of steel and contain vegetation designed to absorb and transpire the collected runoff. Although placed against the existing wall, the green wall structure is entirely self-supporting so it doesn’t contribute any earthquake loads to the existing structure. This was to avoid any potential code-mandated upgrades that may have been triggered if the two structures were connected. The new wall is supported by a large concrete base that treats the structure as an upside-down pendulum.
Akana provided structural engineering to Greenworks, PC, a Portland landscape architecture firm with whom we have partnered on several projects. Funding came from Metro, the City of Portland Bureau of Environmental Services, and the US EPA. The project was completed in September, 2014.