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2c. Vegetation

The Nueva School, Hillsborough, CA

How can vegetation around a school help minimize its negative impact on the site?

Principal architect William Leddy explains, "There's some really beautiful native oak trees and we did everything we could to protect them and literally build the buildings and the sitework around those. We were also careful to protect as many cypress trees as we could." In addition to protecting the natural ecosystem, the tall trees around the school also help to shade the building, reducing the need for additional energy spent on air conditioning systems.

Before construction, the existing site at the Nueva School contained a parking lot surrounded by oak trees native to California, as well as pine trees and cypress trees.

After the construction of the school, many of the large trees on the site remained.

The east side of the library building was constructed partially into the hillside, reducing the amount of earth and vegetation that was disturbed during construction.

What are the soil conditions and native plants around the school's site?

Both the roof of the cafeteria / student center (seen above) and the library have green roof systems. Although the green roofs are located more than 15 feet above ground, they can be considered part of the site because their permeable surfaces contain soil and plants. The soil around the school is approximately 5 - 9 feet of compacted clay over bedrock.

The green roof on the library at the Nueva School contains native California plants, such as seaside buckwheat and various wildflowers, creating a natural ecosystem that attracts birds, butterflies, and bugs. It also helps to insulate the building, keeping it warmer in the winter and cooler in the summer.

Although it might be nice to imagine students hanging out on the roof of the library, it isn't designed to have people walking around on it and it doesn't contain typical grass that you might find on the lawn of your home. Instead, shallow dirt-filled trays, made from a biodegradable material, are planted with several types of sedum plants and then lifted on the roof during construction. These plants hold lots of moisture, are able to filter pollution, and are relatively drought resistant. The trays rest on a bed of gravel to help drain away excess rainwater, as well as a waterproof membrane which protects the roof structure.

The green roof increases the amount of permeable land on the site allowing more rainwater to be absorbed back into the earth, rather than simply running off the building's roof and into the sewer system. Plants on a green roof do not typically grow over 12 - 18 inches tall and do not require extra watering.

Why is water runoff on a site an important idea when designing sustainable buildings?

The rainwater that falls on a site will either soak into the ground if the land is permeable (turf, vegetation), or run off if the material is impermeable (typical roof, concrete, asphalt). Architects and landscape architects typically want to minimize the amount of rainwater that runs off the site because in most cities rainwater drains directly into the sewer system where it mixes with untreated sewage that must be processed and cleaned.

Because the central courtyard space of the Nueva School is a high-traffic area which students and teachers walk across all day, it made sense to cover the surface with a hard impermeable surface such as concrete. But the ground in the courtyard is slightly sloped toward hidden channels beneath rocks and wooden sections to collect the rainwater that falls on the concrete.

This rainwater then runs down a path near the stairs, turning the dry channel (or arroyo) into a mini waterfall during a heavy rainstorm, before soaking back into the ground around a small garden space near the bottom of the stairs. Principal architect William Leddy of Leddy Maytum Stacy Architects explains that this feature is one of the students' favorites. It is "one of several ways that the building tells a story to the kids. Buildings can be teachers", he says.

Students in art classes at the Nueva School have started to personalize and decorate the rocks found in the gardens around the site. These rocks help direct rainwater back to the permeable areas of the site.

http://www.discoverdesign.org/files/topic/video/vegetation.flv
http://www.discoverdesign.org/files/topic/video/vegetation.flv