I’ve had several reasons for designing living roofs and have faced many challenges in implementation. Luckily living roofs can come in many forms and serve many purposes. In this post, I will try to briefly walk you through the second of my forays into this exciting and challenging subject.
For our House Ocho project in Carmel Valley, there were many reasons that we decided to design a living roof. Among those reasons, thermal properties, habitat conservation and fire protection were all important. But the driving reasons were visual. Placing meadow grasses and wildflowers on top of the buildings allowed us to insert our program into the stunning natural site that straddled a grove of costal live oaks and a steep meadow with far less visual impact. Because the house is sunk into the steep hillside and is approached from above, its roofs rather than any facade create one’s initial impressions of the house.
Most of the downhill sides of the house are glazed windows and doors, and because of the seismic activity in the area, we needed to minimize the extra roof loads that deep soil would create. However, we wanted to create a roof garden that had the feel of a native meadow so that the house would blend in with the adjacent landscape.
We worked closely with Paul Kephart of Rana Creek to design the whole roof system. Paul has decades of experience designing living roofs and is responsible for, among many other projects, Post Ranch Inn, The Gap Building in Daily City, and Renzo Piano’s new Academy of Sciences in San Francisco’s Golden Gate Park. For House Ocho, we settled on using six inches of a lightweight soil mix that contained pumas to reduce its weight. We also used a water retention layer that holds a portion of the water in small cups and keeps the soil moist. This basically allows a shallow depth of medium to support plants in a way that is comparable to deeper soil. For plants, Rana Creek worked closely with our landscape designer, Loretta Gargan, and we ended up with a mix of native grasses and wildflowers, as well as strawberry and yarrow. See below for specific planting mix as well as roofing specs.
Intentions: mostly visual, but also habitat and fire protection
Challenges: structural, waterproofing
Solution: American Hydrotech, 6″ of soil, complex mix of native grasses, wild-flowers, and strawberries
OCHO TECHNICAL INFO
The waterproofing membrane is American Hydrotech MM6125 followed by a Hydroflex30 Protection Course and Root Stop WSF40.
The Drainage system is Floradrain FD40 underneath the growing medium layer and ¾” to ½” gravel with perforated pipe and surface drains at the roof’s edges.
The perennial plant species selected for the roof like Sand Sedge, Pt. Joe Fescue, Yarrow and Wild Strawberry are typical of the Oak Woodland understory and representative of the Monterey Peninsula region flora.
A host of annual wildflowers were over seeded in the fall and by springtime tidy tips, lupine, poppies, and goldfields surprised the owners with a colorful spring bloom. These annuals continue to sprout and flower each spring.
Jonathan Feldman is Editorial Director of Green Architecture Notes and Principal of Feldman Architecture.