By: Tomoko Naka
Ever since I encountered a roof top garden covered with a variety of native plants in the early 1990s in Japan, it has always been my interest and dream to help create a “green roof” which is a building roof covered with vegetation. I felt very fortunate that I was included in a recent design opportunity to learn about a new practical approach to creating green roofs in Hawai‘i.
Working together with Richard Quinn, the head of landscape architecture at HHF Planners, I was able to help design a fascinating green roof for an oceanfront residence in ‘Āina Haina, Honolulu, Hawai‘i. The green roof was recently installed by Farm Roof Hawai‘i at a private residence on O‘ahu. Alan Joaquin, president and founder of Farm Roof Hawai‘i, has created a company that is dedicated to turning urban rooftops into productive organic gardens, with a unique modular system that is practical and economical. Other green roof systems were considered during the design stage for this residence, but the Farm Roof System seemed to have the best overall balance of features that made it the right choice for this site and client due to its flexibility in including both vegetables and native plants.
This unique and beautiful house was designed by the world renowned Architectural Design Firm Bohlin Cywinski Jackson of Seattle. The house is situated along the coastline, which makes it a challenging environment for a roof top garden. A concern up front was that the garden set on the roof of the first floor of the residence would be subject to salt winds that would limit the success of plant growth. However, this has proven not be an issue, and the vegetables and herbs are doing great after several months.
Responding to rapidly increased demands in the industry, the green roof concept is becoming a popular architectural and landscape feature in many sustainable projects. In addition to the many benefits to the environment such as lowering the level of carbon dioxide in the air and reducing greenhouse gases, some studies show a green roof could reduce energy use by as much as 30% compared with conventional roof systems.
While it is true that many more green roofs have been installed in recent years, this green roof is quite unique in terms of combining a “working farm garden aspect” and Hawai‘i’s native plants. Sixty percent of the roof garden is filled with ‘aki‘aki grass which is a salt tolerant and low maintenance grass native to Hawai‘i.
The remainder of the roof garden is a working farm garden planted with the owner’s choice of organic vegetables including several micro-greens, arugula, cucumber, radish, and carrots. The family has been enjoying the fresh harvest of plants from the garden at least twice a week ever since its installation.
About 1,500 sf of the roof surface is designed with a series of 14”x4’ woven fabric sock modules, similar to erosion-control compost-filled filter socks, packed with a special blend of rich soil mix by Farm Roof. Between the modules, movable IPE deck panels provide comfortable pathways and working spaces, and also create beautiful contrast against the brilliant colors of the plants.
The green roof has a drip irrigation system with two separated zones, one for the ‘aki‘aki grass (low water needs) and one for the farm garden. The irrigation lateral runs along the roof edge and from there, drip irrigation runs into each planting module. This design provides the owners with the option to expand or reduce the farming portion of their green roof according to their needs.
Whereas a typical kitchen garden is often challenging to maintain beautiful all year round, in this green roof project, the design team successfully achieved a functional garden. It is visually pleasing and at the same time adds an interesting element to a very unique house. It is a great project and I look forward to updating this blog in a few more months with a report on how the green roof is growing.