PANEL 5 Roof Top Techniques
Mark Winterer, Co-Founder/Director of Operations, Recover Green Roofs (Moderator)
Mohamed Hage, Founder, Lufa Farms
John Stoddard, Founding Farmer, Higher Ground Farm
Joseph Swartz, Hydroponic Consulting Services/Director of Farming, Sky Vegetables
(AUD = Audience question or comment)
JSw: I’m a rooftop farmer in urban areas. I still live on a farm in western Massachusetts. I’m a 4th-generation farmer. Joined Sky in 2009 to develop rooftop urban farms that bring sustainable vegetables to urban areas. I run a training facility in Amherst, MA. Now Sky has just installed in south Bronx on rooftop farm on 124 units of public housing. We will be harvesting the first week of April. Next will be in Brockton, MA.
MH: I’m Mohamed Hage, Founder and President of Lufa Farms. I came in from Montreal. Lufa uses rooftop greenhouse hydroponics. In 2010 we set up the first commercial rooftop greenhouse of 31,000 square feet in Montreal. It fed 2,000 people. We are able to recirculate ½ of the heat from a building while growing polycultures. We are looking to expand in the U.S., including Boston.
(brief slide presentation) The first farm produced 1,000-1,500 pounds of food per day. We recently raised funds looking to expand in cities. By 2030, 25% of all people on earth will live in cities. The challenge is to grow more food on less land sustainably.
JSt: I’m John Stoddard, Founder of Higher Ground Farm. Our product is rooftop open farms, essentially “soil” right on the roof. We are getting ready to install a 55,000 square-foot green rooftop farm on top of the Boston Design Center in Seaport District in Boston. We will plant the first tomatoes this spring. My uncle is in the audience. He had a large garden in J.P., so I can speak to the process of getting there.
MW: I’m from Recover Green Roofs. I designed and installed the Higher Ground Farm.
I also did small starter farm on the roof of restaurant in Dorchester. I’ve been working for two years with John. It’s not easy to get plants up to a roof, but it is easier to build and farm in open air. Greenhouses have both advantages and disadvantages. There is a much smaller up-front cost than for greenhouse (about 1/10th), but the subsequent profits are smaller also. Greenhouses have better cost-benefit analysis, higher yield, and year-round growing, though perhaps fewer environmental benefits. Rooftop farming is the most interesting aspect of green roofs. I’m currently designing three others (including one for John).
MH: We do use recirculated water. We capture the leachate, filter it, and reuse it for watering.
MW: John has gone through many hurdles to “get the roof off the ground.”
AUD: It’s a tough environment on a roof, with high winds and so forth. If water capture and recycling doesn’t supply all the water you need, how do you get the rest?
MW: We are lucky in New England because we have a lot of precipitation. But we have to use city water as a supplement. The key is to have as great an efficiency as possible. The advantage is that no runoff goes into storm drains. Hydroponics allow absolute control. We are working with Tufts Univ to see how much water is actually saved.
MH: Hydroponics uses 1/20th the water of conventional rooftop farms. The greenhouse model has the highest restrictions, and has to be managed carefully. We start with runoff. We shunt the water for the first 10 minutes to clean the glass, then divert it to irrigation. We also use snowmelt, and clean it with hydrogen peroxide. Everything is recirculated using drip irrigation. Leachate is diverted to the basement. Nutrients are managed and the leachate is reused. Even what is condensed on the glass is reused. Systems for recapture and reuse are expensive, but new technology is making it cheaper.
JSw: In Urban settings, rainwater hitting rooftops has to go to stormwater drains. This stresses public systems. One inch of rain = 30,000 gallons on an average rooftop. Lufa’s reuse of water recaptures 6,000 gallons, so stormwater loads are reduced.
JSt: Smart irrigation is key. Monitor the rain and don’t overwater. One of the benefits of open green roofs is stormwater. It holds it and slows it. We save a lot of water from the storm drain.
AUD: Steve (Researcher from PA) – Mohamed, do you add supplemental CO2 to the system?
MH: Yes. We actually run out of carbon dioxide in our hydroponic systems, so we get extra carbon dioxide for the plants from a nearby brewery.
AUD: Steve – Hydroponics was done in the 1950s. There were problems in maintaining a rhizosphere, microbial communities that contribute to the “normal” growth of plants. Are hydroponics adding microbe communities?
MH: We are studying this. We are adding microbes to the water. Polyculture helps us. We inoculate the substrate with microbes and fungi.
MW: Organic food studies show a higher nutritional content.
MH: I’m from Lebanon and I’ve always had organic gardens. Hydroponics is like driving
a manual car, can tailor and tweak to create anything the plant needs.
JSw: The actual nutrient content in food is proportional to the nutrient content in the soil. Research shows that organic food compared to “big ag” is better. Sterile soil equals low taste and nutrition. There is not so much research on hydroponic food. Nevertheless, hydroponic method produces plants that are “like an elite athlete.” They perform well under selected conditions. We tailor the input chemicals to create a growing environment that produces a product with “maximal nutritional value.” In essence, we grow a “nutrient-dense plant.”
MH: I brought some sample food just to look at. Hydroponics can grow so much food per square foot. When I was in Lebanon, I had to travel over a hill to get asparagus. Then I would bring it back home and my mother would use it to make the most fantastic omlette. But we need to feed 7 billion people. You can with hydroponics if you pick the right conditions.
MW: We have a short growing season in Massachusetts – only 110 days.
AUD: How do you determine if a roof is appropriate for rooftop farming?
JSw: The geographic is important. You need good sunlight, but also zoning permits, a good market, availability of truck routes and so forth. Who will eat the food, and where do they live? Greenhouse systems are low-weight and have few structural issues, but structural integrity is still important. Who we are feeding is important too.
MH: It costs three times as much to put a greenhouse on a roof as on the ground. Our vision is to grow within a city and bring our product to consumers at a competitive price point. Just like solar power, our technology costs have come way down.
JSt: For rooftop farm of this size, the roof needs to have a reliable membrane. You also need to prevent falls while providing access. My company will have people on the roof for classes and viewing the farm, so it needs to be accessible and safe. An enthusiastic landlord is key.
AUD: What is the size of the roof you need?
JSt: It should be large enough to accommodate a farm of at least 25,000 square feet. We found a roof with 55,000 square feet.
JSw: Zoning is usually not a problem in these projects, but resistance can come from the neighbors when proposed. They are sometimes bothered by the appearance of a rooftop farm on a neighboring building, or concerned about the weight, safety, and leaks.
AUD: What is the timeline for these projects?
MW: For me it has been 2-1/2 years,1-1/2 years part-time to find the roof, 1 year for design. The permitting is still to come. The total time will be about three years from the initial agreement.
MH: It took me 3-4 years initially for my projects. Now it’s about 1-1/2 years from start to finish. It’s still a challenge, and we need to come down to under 1 year for it to make sense economically.
JSw: The Bronx development started two years ago, and just began operation last week.
MS: One project went in quickly, but we had “guerilla roof” of 5,000 square feet in Dorchester. It took a year to build.
Q: What are the pros and cons about growing vertically, even up up the sides of buildings, as opposed to roofs?
JSw: Some hydro systems do use vertical techniques, but they are not very efficient, certainly nothing that is commercially viable.
MH: Vertical farming inevitably involves some artificial light. It’s not sustainable economically, ecologically, and not necessary. There is more sun on a roof. When we exhaust all the space on all roofs, we can look at it as an option.
AUD: Stephen Herbert, University of Massachusetts, Amherst – I am familiar with one person who used a shipping container with LED lights and also growing on the walls. He has gotten over 6,000 heads of lettuce in a very small area.
MW: Vertical farming is much more expensive, though it may be suitable for some vine crops under the right conditions.
AUD: What are the concerns about air pollution and its effect on the rooftop crops in urban settings?
MH: Pollution tends to stay low, within a few meters of the ground. The air is much cleaner up high, and there is more of a breeze. A greenhouse has its own microclimate. There are filters and humidifiers. We have seen no problems with air quality in two years.
JSw: There are clean air standards in the U.S., but they regulate air quality at much more stringent standards than that which would affect crops, even in cities. It is not a problem.
JSt: Alex (Axtl or Baxton ??) in New York City has been doing research on that, and has found no detectable pollutant problems. If you are more than 700 feet from a highway it is fine. Air pollution is more a problem for breathing than eating. The soil in a rooftop greenhouse is a special blend that will not have pollutants in it.
AUD: John Lipman, Lipman Development Strategies – Is there anything financial that government is doing to support this? For example, if a rooftop farm is catching leachate and runoff and reducing the strain on stormwater systems, it seems that city governments might provide some type of rebate in taxes or other financial benefit. Could rooftop farming significantly reduce fiscal costs, and could the same be done to mitigate stormwater on ground-level urban farms?
MW: I believe the question you are asking is can we offer our farming as a stormwater management practice, and get benefits from it from the cities?
JSw: It’s a no-brainer. Cities do encourage it and appreciate it, but they will not reward it financially. The Boston Museum of Science has expressed a strong interest in this, as they are right on the Charles River. It’s a very important tool.
JSt: Anytime you add permeable surface, you will be treating stormwater. My hope is that in 10-15 years, we will see rooftop farms and greenhouses all over. Some cities have tax incentives, but not Boston yet.
MH: Nothing beats green roofs for stormwater capacity. You can collect three days of water for your operation after 15 minutes of rain.
MW: We have been working with the Boston Redevelopment Authority (BRA) and we are meeting with the Boston Water and Sewer Commission next week. We have to show that we can contain water from runoff. Near wetlands in Massachusetts you must retain 60% of runoff, so this rule is good for marketing of rooftops farms, since the building gets ecological points. We need to use this technology to reduce input on the environment. For open systems, we are trying to amend the soil to retain nutrients. Biochar and peat moss work well, though peat moss is a non-renewable product.
AUD: Stephen Herbert, University of Massachusetts, Amherst – The other part of the previous question was can you connect runoff at the street level with either rooftop or ground-level gardens?
MH: The former Mayor of Portland, OR advocated green buffer areas and vegetated swales to mitigate and filter stormwater. It’s much harder to grow agricultural products in that environment, but it’s good for other plants.
AUD: I work at a hydroponic farm in Dorchester. What is the sustainability of the chemicals and nutrients used to run the rooftop farm, especially on water?
JSw: We actually use very low total amounts of chemicals compared to regular farms.Compost extracts are dissolved in water. For example, nitrogen has to decay into nitrate before being usable in the soil. Thus it is uncertain how much nitrate you are actually adding to a system when you add the unprocessed nitrogen-containing material (e.g., manure). We produce the nitrates directly in the water, which has much less impact than traditional agriculture.
MH: Ditto, hydroponics uses much less nutrient. A typical plant will leach 80-90% of the nutrients it receives. Hydroponics allows much greater control. We capture and reuse the chemical water. We compost the green waste and sell it to consumers. We can’t use ourselves as it is too ill-defined chemically, and has unknown microorganisms. The revolution in hydroponics will be in developing techniques to use compost.
Q:What is the cost per square foot of growing on rooftops?
MH: The first rule is that it has to make money. It costs $50-60/square foot to build a greenhouse on a roof. Once the farm is up and running, it works very well with very small inputs. It uses half the energy and much less chemical input than a regular farm. Food can be delivered as soon as is ripe to the very city where it is grown, with reusable packaging and no waste. It takes 4-5 years to payback the investment. We initially spend about $2.5 million/acre, and do as much as $2 million/acre in business, even better when we sell direct to the consumer. A good supply of workers can be found in cities: they had 3,000 applicants for 3 positions to work in the greenhouses. When you add it up, it is a big but very good investment.
JSt: For open rooftop farms, it costs much less, about $7/square foot to build, with revenue about $2/square foot per year, similar to other urban farms. Urban farms are not just a farm but also a destination, and can include things like classes, dinners and so forth. People want to see it. It takes 5-7 years to become profitable.