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Green Roofs and Living Walls

May 7, 2012
Barbara J. Euser

Perhaps the idea originated with the Hanging Gardens of Babylon of 600 B.C.E. The ivy-covered walls of sixteenth-century manor houses continued the practice. The sod roofs on nineteenth-century frontier prairie dwellings may have been more necessity than choice. For a number of reasons, green roofs and living walls have been around for thousands of years. With current interest in sustainable landscaping practices, these historic techniques are attracting new attention.

According to one definition, sustainable landscaping “comprises numerous practices that address environmental issues related to the design, construction, implementation, and management of residential and commercial landscapes.” The environmental issues sustainable landscaping addresses include global climate change, air pollution, water pollution, water shortages and drought, storm water management, pesticide toxicity, soil health, fertilizer run-off, non-renewable resources and energy usage.  

Green roofs and living walls address a number of these issues. They can 1) reduce the heat produced by urban environments; 2) improve air quality due to the filtering mechanism of the plants and substrate; 3) improve the quality of water, for example water running off a green roof can be used inside the house for flushing toilets; 4) significantly reduce the surface runoff of rainfall, thus reducing storm water management requirements; 5) reduce the need for air conditioning and provide a degree of insulation in winter; 6) provide sound insulation from the combined effects of soil, plants and trapped layers of air. Additionally, green roofs and living walls can provide habitat for insects and birds and provide efficient green space for recreation and for growing flowers and vegetables.

Green Roofs: As American pioneers knew, green roofs provide insulation, allowing houses to remain relatively cool in summer’s heat, although sod roofs were notoriously leaky and dirt could filter through cloth ceilings. Today’s green roofs provide similar insulation benefits, but protect the building with an impervious waterproof layer, covered with several different layers of substrate, topped with plants that are able to withstand harsh conditions. One of today’s most popular green roof plants is sedum, a succulent that can tolerate long periods without rainfall. Using several different varieties of sedum, one may create colorful patterns. One landscaping company suggests that a company’s logo can be planted into their roof, providing perennial advertising!  Grasses, wildflowers and any number of —preferably native—plants may be employed.

Plants and substrate are heavy and this is a major consideration in determining whether or not an existing building can support a green roof. The pitch of the roof is not: landscapers plant green roofs on pitched roofs as well as flat roofs, carefully anchoring the substrate at intervals on a pitched roof.  The initial cost of a green roof is higher than that of other roofing materials. However, annual maintenance costs can be relatively low. Because a green roof protects the waterproofing membrane on the roof from the elements and ultra-violet light, the life expectancy of the membrane may be doubled or tripled, thus reducing the overall cost of the installation.

Living Walls: The most basic living wall is a vine, planted in the ground next to a building, which climbs up the wall, clinging with its own tendrils: ivy is the best-known example. Ivy leaves may turn red in the fall, adding additional charm. However, the tenacious tendrils may loosen shingles. Ivy should be trimmed back or torn down periodically to keep it from becoming an attractive dwelling place for rats and other small animals.

Living walls may also be created by plants planted above the wall that grow downwards, for example “climbing” roses cascading down a staircase.

Living walls may be interior as well as exterior. Years ago, I cultivated Swedish ivy in a row of planters placed along a shelf high on a living room wall. The Swedish ivy eventually hung all the way to the floor—nine feet below the planters. The room was filled with natural light, indirectly available to the Swedish ivy. The plant-hung wall was the most striking feature of the room. I appreciated its beauty, but  I was unaware of the health benefits to my family: increased oxygen due to the natural process of photosynthesis and increased humidity due to transpiration.

Today’s living walls may take the form of planters on the ground or suspended on the sides of a building, with steel cables or mesh attached to the wall to support the plants. They can be next to building walls, providing insulation and protection for the wall surfaces—from the elements as well as from graffiti, or at a distance from them, providing a green screen against unattractive construction. Commercially available planters feature angled containers for individual plants that, as the plants mature, create massed walls of foliage. These planters may be used outside or inside. Interior designers incorporate living walls into residential and commercial décor because of plants’ various colors and textures, as well as their calming, serenity-inducing effects. 

The ancient Babylonians appreciated the value of being surrounded by plants—growing on roofs, hanging down walls. Today, as we focus on sustainable landscaping, we are rediscovering their wisdom.

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