Page 177 - The Green Building Bottom Line The Real Cost of Sustainable Building

156 CHAPTER 5

uct contains 95 percent recycled material. All of the wood used on the project was
sustainably harvested and certified by the Forest Stewardship Council. Building Shops
600 has provided us the opportunities to experiment with our first vegetative roof—
an intriguing idea we hope to use on future building projects—and using solar energy
for water heating. The building’s small size makes it an excellent laboratory for
experimenting with new (to us) techniques.
The vegetated roof—four inches of engineered soil over a thick rubber mat (thicker
than a normal roof membrane)—covers 9,000 square feet of the roof, which is more
than half the building. The soil is planted with several types of drought-tolerant plants.
(We’re still experimenting to determine which ones work best in our climate. We
started with four species of sedum; one of them is growing well.) This “garden roof”
captures and retains rainwater, eventually returning some of the moisture to the air
through evapotranspiration, the combination of the evaporation of water from the soil
and transpiration of water to the air through the leaves of plants. The garden roof pro-
vides additional insulation to the part of the building it covers, and it helps protect the
roof from damage caused by sun and pollution, more than doubling its life expectancy.
The remainder of the roof area is covered by the same type of bright white, high-
albedo membrane as the other flat roofs on the property. Refrigerant units, which are
CFC-free, were installed on top of the membrane. Both the garden roof and the white
membrane help mitigate the heat island effect.

Figure 5.6 The green roof atop Shops 600.