Leaf Litter

Leaf Litter Talks with Bob Cameron

We chat with PhD candidate, Bob Cameron as he shares his excitement about green roof and living wall technologies.

By Amy Nelson

Article Index

Robert D. Cameron is pursuing a Ph.D. in Horticulture at Penn State University after several decades in industry directing the environmental programs of a diversified multi-national. Bob’s areas of focus are sustainable technologies, including green roofs, living walls, and constructed wetlands, and the evaluation of these technologies at a molecular level to improve design efficiencies. Though his concentration is on green roofs, he has a palpable passion for living walls. Rumor has it he’s even installing one in his shower at home!

We were thrilled to have the chance to chat with Bob in the horticultural greenhouse at Penn State University.

Why living walls?

My question is always, “why not living walls?” From an aesthetic standpoint so much of our interior and exterior architecture is ugly. Especially some of our buildings that are strictly concrete or masonry and have no covers on them. By coating them with plants, there are so many benefits. You have already discussed the benefits of green roofs. Many of those parallel with the benefits of a living wall. It just makes sense to incorporate plants into our environment. They clean the air and can be integrated into graywater treatment systems. Living walls on masonry structures in urban areas can reduce noise pollution.

A green roof can be an “island in the sky.” If you’re looking at them from a habitat standpoint, it may make sense to be able to connect a green roof to ground level via a living wall. For a green roof designed for stormwater runoff, connecting a living wall can further detain and treat rainwater. The living wall can become a functional part of your landscape architecture.

Describe the anatomy of a living wall.

There is a little more variability with a living wall than there is with a green roof, depending on what you’re trying to accomplish. A thin film [as is used in the orchid wall in the Penn State horticultural greenhouse], has a lot of applications with an interior, where you don’t want the mess of soils in a house. It can also be used exterior, providing a small air pocket between it and a masonry wall, as long as you provide an irrigation system for it.

There are larger, wider systems. If you want something with less maintenance, you can do those. If you want to provide an insulating factor for a wall, you’d go with a much larger dimensional wall. There is so much variability.

Remember, living walls are very new. Green roofs have been in Germany for 40 years. In the U.S., much less. But living walls have even less of a history. At this point, there is no one design for them. So many people like us are experimenting with different materials to see what makes the most sense.

Can you give us the 30 second history of living walls?

There are examples of green walls from 2,000 years ago. We know that the Egyptians used different types of biofilters to treat waste water and to apply opportunities for gardening in their urban areas.

In modern times, I think primarily of Bill Wolverton. Back in the late 70s, Bill was with NASA, and he was looking at biological ways of treating wastewater for the future space station. He had done some very creative uses of constructed wetlands, and then began looking whether we could use some of those plants to address indoor air pollution. Bill was really a pioneer with some of these initial applications.

Green roofs, living walls, and constructed wetlands are all examples of biofilters. Taking people who have worked with biofilters and realizing that this is all a matter of geometry – how you place these things. There in is how living walls were born.

What’ the most exciting thing happening today in the world of living walls?

There are a number of areas. Integrating them with green roofs and constructed wetlands greatly expand the versatility of living walls. Developers and planners are beginning to realize that we don’t need to build treatment mega plants and transport waste for miles to them. Why not look at our buildings as standalone entities, whether it’s from an energy standpoint, wastewater, etc.?

The extension of that is: we need to change our vocabulary and quit using the word “waste.” If we begin to look at our buildings as their own enterprise, wastewater is really an unused resource. How can we take that resource, recoup the inherent energy out of it, and then reuse it back to that building? Living walls are an integral part of that solution. They can allow us to clean the water and reuse it for flushing commodes. When you think about it, why do we use one of our most precious resources – potable water – for flushing commodes? It makes no sense. It’s the same way with materials. Here we are, in the midst of an ongoing energy crisis, and yet what are the two most common building materials we use in the United States? Asphalt shingles, which are made of petroleum, and vinyl siding, which is made of petroleum. So we wrap our architecture in oil! Living walls provide a sustainable alternative to that.

Have you ever had naysayers comment that living walls seem energy intensive (since some of them have artificial lighting, complex irrigation systems, etc.)?

It’s all a matter of design. There are some notable “green” projects that are anything but green. Designers need to utilize tools such as life cycle analysis to ensure designs are sustainable.

We had a student from Ghana, where very little water per person is used and it is very valuable. We worked with her to design a system to treat gray water that could also be used for food production. For them, just to get some tomatoes…that’s a high value crop. If they could have something outside their door where they take water, after is has been used several times, recycle it and produce some tomatoes, it’s turned the water from waste to a resource. The issue was doing a pump. So we were looking at something that has been used successfully in other projects: having a stationary bicycle, like one you’d see in an exercise room, that village children could come and ride, and have a great time watching the water go up and around. We find that you don’t need to provide circulation 24 hours a day. Actually, these systems do better with intermittent flows. Just to have a child come over periodically, get on the bike and have fun, and pump it, you would have a very low energy way of providing irrigation.

Living walls really should not be high energy systems. In their infancy, many of these technologies start off with materials that may not be perfect. That’s where research comes in to find more sustainable materials.

How are living walls better than a typical air or water filter?

Let’s look at the NASA program as an example. In the future, we’ll colonize Mars. Do you want to be transporting materials back and forth at an outrageous cost – materials with a mechanical filter that you have to throw away and reproduce? It’s not a sustainable model. Using that same logic on Earth, why should we be taking mechanical systems that are using up resources and then get tossed afterwards, and have to be transported?

Why not use a biological system that you grow? We need to get away from the way we’ve developed industry around producing an item that goes through a certain life and then has to be thrown away.

When you look at the life cycle analysis of a green roof or living wall, that’s where the superiority comes in. Use the analogy of an asphalt shingled roof. You may be lucky to get 15 years out of a 30-year asphalt shingled roof. So many of the numbers that people crunch to see how effective these are only go out a decade. What you need to look at is, over the course of so many years, how many times do you have to replace that roof?

Living systems are, by far, superior. That does not mean they are without maintenance issues or certain types of negatives. They are living systems. If people add an herbicide, pesticide, or something else to it, they will disrupt that biological cycle. It’s not a perfect system, but I think it’s far superior to comparable mechanical systems.

What are some of the challenges to living wall constructions- in terms of logistics, maintenance, and your overall carbon footprint?

All biofilters are the same. The same issues you’d have with green roofs and constructed wetlands, you have with living walls.

First, there’s permitting. So often, local regulators have not yet developed permits for these. So that becomes an issue. If you’re putting up a large, two-story wall, you have structural issues. The last thing you want is for a wall to come down on top of someone. The same is true for green roofs. We have to make sure our buildings are sound and designed for the load. So many regulators are unfamiliar with these technologies. That brings us to the second challenge.

Lack of familiarity makes people feel uncertain so they’d rather not have [these technologies] and go with traditional types. If you’re looking at wastewater systems, living walls would be considered “experimental.” The hurdles you’d have to go through with most local regulatory agencies are much greater.

Like so many designs you do in a building, you have to make sure you’re designing these units for the site. If you have an area that’s in an alley that gets zero sunlight during the day, you don’t want to put a living wall with a bunch of plants that require a lot of sun. These are some of the common-sense things you have to deal with.

It looks like green roofs are beginning to have some influence on the way buildings are designed. Is this happening yet with living walls?

I think they are much farther behind. Green roofs are still in their infancy in the U.S. Living walls are just after conception.

Are there any other “surfaces” that people are thinking about “greening?” Are people starting to put green roofs and walls on cars and trucks?

Well, if you have the ground, the vertical and the roof structure, you have the opportunity to apply this technology to different places. Other than a “wow” factor, I can’t see much practicality to green roofs on cars. But, it certainly makes for an interesting site!

One of the newer concepts people are talking about is wet roofs. Certainly, it can increase the diversity of a roof, be functional and an aesthetic feature. However, water adds a lot of weight on a roof, and improper design could create numerous problems. Also water is a precious commodity, and in some areas, the local regulators say, “thou shalt not take our (rain) water.” But, incorporating biofilters such as living walls into our building designs are forcing us to reevaluate our notions of architecture.

Got an idea?

Contact The Editor

Sign up for Leaf Litter

Browse by topic

Browse by year