mixtures. They are typically found in California's native serpentine grasslands, which
feature shallow, nutrient-poor soils.
There are five different green roof areas,
totaling 5,375 square feet. One is partially
covered with photovoltaic panels.The
rooftop wildlife habitat is not intended for
tenant recreation or public viewing, but
three small garden roofs at each upper floor
are visible from apartments, hallways and
decks, which will display vibrant colors and
textures throughout the seasons for the daily
enjoyment of building occupants.
Each roof includes a waterproof membrane covered with 3 to 6 inches of specialized soil mixtures.The upper roofs were
planted with scattered seeds. Rana Creek
was involved in developing a biodegradable
modular planting system made from coconut shells, called BioTray, that was used for
the project. For the lower roofs, the plants
were grown at Rana Creek's nursery and
transported to the site in 4-inch deep BioTray baskets, which provide both erosion
control and thermal resistance.
The green roofs at Casa Feliz provide a
continuous layer of R-30 insulation over the
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building spaces below, eliminating the thermal breaks that result in energy losses in
standard wood-frame roof assemblies.The
mass of the living roof combined with the
water retention capacity minimizes "thermal
shock" to the building from varying high
and low roof temperatures, thereby moderating temperature fluctuations inside the
building and reducing the need for heating
and cooling.The roof provides free evaporative cooling on hot days and high insulation
value on cold days, keeping the roof at a relatively stable temperature.
Although there are additional costs for
installing a living roof, particularly for increased structural load, Jeff Oberdorfer, executive director at First Community Housing,
estimates that it added about half of a percent to the overall construction cost, which
was offset by eliminating the required storm
drain upgrade.
To track the performance of the living
roof, FCH installed an Agilewaves resource
monitoring system. A weather station measures rainfall at the site, and water flow
gauges at the roof drain measure runoff, enabling the developer to calculate the actual
water retention capacity of the living roof
and demonstrate the reduced burden on the
city's storm drain system.This performance
data will be used to educate the building industry and policy makers about the benefits
of green roofs with the goal of encouraging
wider spread adoption.
As San Jose's first development with a living roof, the project acts as a prototype and
educational resource for other municipalities, developers and communities. Casa Feliz
"has been a model for incorporating water
conservation features in affordable housing,"
said Oberdorfer.The project team hopes that
the success of Casa Feliz's living roof experience will plant a seed to inspire others to
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plant their own rooftop gardens.
Maryanne Welton has been a project manager
with Rob Wellington Quigley, FAIA, for 34
years, leading design teams on a variety of affordable housing and civic buildings.
Article courtesy of Green Roofs for Healthy
Cities (GRHC), and was originally published in
GRHC's Living Architecture Monitor:
www.livingarchitecturemonitor.com.
Landscape and Irrigation 9
