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Part 1: Demystifying Living Walls – Facts & Fiction
Living walls are igniting the imagination of designers everywhere. And what is not to like, for as encapsulated visions of nature with their seemingly perfect beauty contained on a wall or screen, they tend to idealize nature in the urban realm.
So let’s talk about living walls and demystify some facts and fiction. Not the kind of walls that have existed naturally on a rocky cliff for the past thousands of years and not the traditional “green” wall that is composed of vines such as ficus pumila or bougainvillea voraciously growing up a building façade looking as if the architecture is being consumed by nature; and, not even the romantic notion of a hanging garden wall a la the Gardens of Babylon. While all of these planted walls are lovely to look at they are not the new urbanized version that is getting the heavy media play today especially in the green building industry. With the onslaught of sustainable ideas and products touting their green credentials, many terms such as “living walls” are being used without a shared understanding of what they really mean and how they really perform. Yes they include plant material but are they all environmentally sustainable? Are they easy to construct? What about maintaining them? How much do they cost? How well do they perform as a sustainable model? Do they really provide for better air quality? Well, if you are as curious as I am, then come along for a little exploration on what living walls are all about.
Definitions: So let’s start with a definition and agree that a living wall is not the same as a green façade wall. In the book “ Planting Green Roofs and Living Walls” by Nigel Dunnett and Noel Kingsbury, they state that green façade walls are vertical structures that to the eye are clearly part composed of hard construction materials and part composed of vegetation. Gabion walls, stacked stone walls with planting niches, and stacked modular walls, are all variations of a green façade wall. In all of these examples, the plants are rooted behind the façade or apart from the façade. Green façade walls also include systems such as GreenScreen, a 3D metal grid system, and steel cable systems like Jakob that provide a 2D grid surface for a plant rooted in the ground or container to grow on. The limitation for these two grid systems is the length of the plant’s vine leader ( typically 10 – 30 feet) that is chosen to grow on the surface. The difference with the grid facade system and the stacked façade system is that one is semi -transparent and the other is solid.
According to Dunnett & Kingsbury, living walls are differentiated from green façade walls in that they are vegetated walls that are composed completely of vegetation. These living walls are composed of plants that are rooted into some sort of growing medium on the outward face of the wall rather than behind the facade of the wall. And, similar to green roofs, these vertical gardens exploit previously underutilized upright structures. Hydroponic systems, vegetation mats and living fences are all types of living walls.
Hydroponics: Pioneered by Patrick Blanc, a French researcher and designer, and celebrated tropical botanist. This system is based on growing plants without soil using balanced nutrient solutions to provide all of the plant’s food and water requirements. This is a relatively thin system and the primary components are a wool felt blanket material for root propagation, a waterproof backing such as PVC sheet, a drip irrigation system that keeps the felt constantly moist. Generally there is a re-circulating pump and a water collection base at the base of the wall. Once established, their maintenance is limited to annual clipping and removal of dead foliage, but that is if you have really done your plant selection homework well. A recent failure of note from one of my sources, was the planned interior moss wall at The California Academy of Sciences in San Francisco which just couldn’t get the light and water nutrients right so it was eliminated before the museum opened. Though typically quite visually stunning, these wall systems are very intensive in their resource requirements and water dependence so not for the faint of heart or strapped pocketbook. Energy use is higher than other living wall types.
Vegetation mats: These systems are similar to green roof technology where vegetated mats are grown and then laid into place on the roof surface. Because most modular systems in existence started out as green roof technology, most vegetation mats consist of drought resistant sedums. The reality however is that wall environments are harsher than a rooftop as they are not free draining, typically in a location that does not receive direct rainfall or direct sunlight and are buffeted more directly by wind. Add a thin layer of soil substrate and the additional shade effect on the lower portions of the wall and you have a less friendly plant environment than a roof top. Vertical sedum walls seem very lush and pristine but their long term success is not guaranteed. In fact just recently the succulent wall at Flora Grubb Nursery which has launched a thousand imitations in the past two years since photographed, was looking very tired and not so photogenic for this very reason. Since succulents move and grow leggy as they mature, many of the succulents had left there specific planting spot and thus vacant areas of substrate were in evidence. Techniques such as additional drip irrigation and pinning of the mats to hold soil and plants to the supporting structure, may help prolong the life of these systems. Some vegetation structures such as Tourensol SiteWorks and Green Living Technologies angle the support structures for the vegetation to overcome the additional shading and add to the water capture ability. Some of the companies with the modular systems allow designers, ecologists and landscape architects the ability to collaborate on the plant pallette to be used and some do not, keeping to more commercially viable alternatives to limit their liability exposure. In general, more collaboration will allow for greater biodiversity and habitat to be developed in these systems.
Living fences: The two vegetated structures above are primarily one dimensional – presenting only one face to the viewer and growing in one plane. Similar to the idea of a hedge that can be viewed from any angle, freestanding, three dimensional living walls can provide the same effect. A wall not rooted down can also be moved around and may have less maintenance than a hedge since a living fence will always stay the same size and can provide instant impact. These systems consist of a framework structure that keeps the system upright, vegetation layers and an internal growing medium such as soil. Known also as “Fedges”, a timber or metal framework holds a wire grid such as chicken wire on both sides to contain the growing substrate. Some use a geotextile mat to stop the substrate from spilling out. Slits in the fabric allow for plants to be inserted in the walls. Drip irrigation is typically added to maintain the vegetation cover during dry periods.
Performance Metrics: A living wall is an urban constructed wall composed of vegetation and functioning as a vertical garden. Water, nutrients and a growing medium are all necessary for the vitality of the planted wall. Some techniques are resource intensive (water and energy) and others less so. Living walls can reduce the energy we need for buildings- similar to green roofs insulation performance. They have the ability to add to the carbon sequestering of the project, can provide passive solar heating and cooling, cleaner air quality since the square foot plant density is more intense than horizontal plantings, reduce the heat island effect, provide habitat including for endangered species, they add beauty to urban environments, connect people with a bit of nature, maximize tight spaces by going vertical creating more habitat for both people and the environment in the city.
There are not many documented case study reports on living wall performance metrics since this is fairly new trend in landscape architecture and urban design. This type of information needs to be presented in a case study report to better analyze the data and understand the performance metrics on a more global scale. Metrics will most likely vary widely depending on climate and microclimate issues and selected plant types. During the pilot phase of the Sustainable Sites Initiative, some of this data may become more available if there are projects that will include living walls.
Personal Experiments: I have been experimenting with a few wall prototypes myself as I would like to incorporate more into some of our projects in California but need to understand the pros and cons better. My first wall is a wooden frame, hand watered one like the ones Flora Grubb offers. I did this one as an “eat my wall” prototype as I am interested in urban farming aspects of the walls too. I am finding that succulents and sedums are faring well as expected as are certain edible herbs such as lettuce, thyme and mint. Other plants are not fairing as well. When not on a drip system, the results depend on how good of a gardener you are in maintaining it. My next wall experiment will be dripped from the rear with a layer of felt fabric or geotextile for root stimulation to see if the plants thrive better. Most other green or living wall designers my office, April Philips Design Works has talked to, consider the geotextile fabric to be one of their trade secrets so we have yet to know which ones are performing better than others. Later in the year we will be building a “fedge” from chicken wire with layers of drip within it. My office is also in the process of doing the first phase of an edible organic school garden using wall mounted woolly pockets for our first harvest edibles so I will be looking closely at this product’s performance over the next few months. I like the woolly pockets for their “instantness and accessibility”. Their geotextile fabric is called PET and is made from recycled plastic bottles. While I have seen some very beautiful living walls at various garden shows and lots of expensive Do it yourself kits available now in the retail market, most have not been around long enough or scientifically and rigoursly documented to see what the longevity factor is. A big unknown is what their true value is from the carbon footprint aspect. Living wall art is a great a great do it yourself website that has lots of ideas for building living walls if you are interested in doing your own homework experiments.
Professional Sharing successes and failures: In a recent LinkedIn blog discussion started by Larry Lesser of Rana Creek on what do we really know about green walls, we had a lively back and forth about the topic across the country. Dean Hill. ASLA, CGP said “As designers, WE are responsible for matching the plant selection, irrigation design and maintenance commitments within the right system and intended use. In addition, I think that it is our responsibility to manage the client’s expectations. Interested clients might see pretty pictures and think that they’ve got to have one, but we need to take the opportunities to educate them so that their expectations will be met, especially with green wall systems (facade and living).” There is also a web site within LinkedIn called Green Mojo just for green walls that is askign some of these same questions for those interested in furthering the conversation. A recent exhibit at the San Francisco, AIA, that focused on living walls included innovative ideas, actual wall system components, and artistic installations. These type of exhibits are helpful to furthering the design dialogue of these features that are now blossoming in the public realm. We need more discussion and more sharing of the data to continue the exploration into their pros and cons.
A few Tips for successful living walls:
While much still needs to be docuemented, there are a few key factors that will insure more success in designing and installation of a living wall. In general, costs of these walls vary widely. They are more expensive per square foot than horizontal garden plantings, and can be on par with living roof system costs. Some cutsom ones are even higher as the the amount of plants per square foot is extremely dense for the instant effect and the frame can be elegantly designed of a high quality material too.
1. Match plant selection, watering design, and maintenance commitments with the right framework structure and intended program use. Talk to the client to manage their expectations. Understand the construction schedule impacts as well.
2. Know your resources well and use them wisely – conservation and regeneration should be always thought of when making design choices. The more you can design a circular loop living system, the better chance of success.
3. Look at plants in your region that are suitable for roof plantings and look at the spontaneous flora on old walls in your region. Know your climate responsive plants (and natives) well but also the microclimate aspects created by the wall system. Biodiversity adds to the health of the ecosystem.
3. Harness appropriate bioengineering techniques. Technologies improve every year so do your research and know the pros and cons of your approach.
4. Link landscape systems to building systems and be innovative in thinking how to incorporate water and natural systems into the whole development, not just the wall. Remember, where water flows, plants grow.
by April Philips