there’s nothing like a heat island

When travelling from my forested neighborhood to Center City Philadelphia, the change in temperature is often startling.  The commute is only ten miles, and yet the temperature noticeably warms by at least 5° F when approaching the city.  This globally ubiquitous phenomenon, known as the urban heat island effect, occurs when urban development replaces vegetation, soil, and open water with impermeable surfaces such as concrete, asphalt, and dark-colored roofs.

Philadelphia, PA || Image by Google Earth

Environmentalists tend to sneer at the thought of the urban heat island effect, which wreaks havoc on natural ecosystems and contributes to global climate change.  But what if we ReThink this deleterious phenomenon and leverage it to our agricultural advantage?

The warmer the climate, the longer the growing season.  This implies that cities can be used to cultivate fresh food for a slightly longer time span than can rural environments.  Extended growing seasons are particularly relevant in cooler climates, whereas warmer areas (such as California and Florida) can easily grow food outdoors year-round.  Cool-climate farmers often artificially extend the growing season with greenhouses or high tunnels.  These structures can be prohibitively expensive for many novice growers, which means that a naturally-prolonged growing season becomes increasingly attractive.

Of course the ultimate objective from a landscape architectural, urban design, or ecological perspective is to minimize the urban heat island effect altogether.  This is a lofty, yet tangible goal, which will take many years of design and development to reach fruition.  In the meantime, let’s leverage this heat and  grow some food.

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a financial giant and a pitchfork

While young metro-agrarian trend setters around the country dive elbow deep into compost, one financial giant wants to get its hands dirty too.  This multinational investment banking and securities firm (that prefers to remain anonymous), is constructing a raised bed production area on the roof of the firm’s newly acquired hotel in Lower Manhattan.  The hotel is located in the affluent Battery Park City neighborhood, and will contain a restaurant that aims to incorporate rooftop produce into its menu.

Cedar for raised beds || Photo by Lauren Mandel

The sophisticated rooftop design incorporates swaths of extensive green roof, decorative crushed glass, and rubber pavers in addition to the farm plots.  Ken Smith Landscape Architect designed this layout, and hired Roofmeadow (the green roof firm for which I work) as the project’s green roof consultant.  Roofmeadow maintains a national network of licensed green roof contractors, one of whom, the Sponzilli Landscape Group, is currently installing this project.  I had the good fortune of visiting the site this morning to perform construction oversight, and was able to see the farm plots first hand.

The raised beds themselves are much like those on the ground plain, except that these beds more intricately address the threshold between soil and underlying substrate.  Rooftop raised beds require a well-planned drainage system in order to maintain proper soil moisture in each plot.  A bed that does not drain effectively can become waterlogged and kill the plants growing within.  A bed that drains too quickly will require significant levels of irrigation, and will therefore produce weak plants while wasting water.  The Embassy Suits Hotel raised beds utilize specially engineered growing media that holds a specific amount of water between its particles.  This media sits on top of a sheet drain, which was selected for its specific transmissivity (or horizontal flow) rate.

Installing raised beds on a roof is much more expensive than on the ground, due mostly to costs associated with rooftop access and labor.  This means that the beds themselves should ideally last much longer on a roof than on the ground, so that they do not need to be replaced very often.  What material should be deployed, then?  Untreated wood typically lasts 3-4 years when used for raised beds in the northeastern climate.  Treated wood lasts longer, but proves toxic when containing edible crops.  Cinder blocks and brick are sturdy options, except that they can easily exceed rooftop weight limits.

Ken Smith Landscape Architect chose cedar for the raised beds at the Embassy Suits Hotel.  This wood naturally resists decay, and therefore acts as an ideal candidate for long-lasting rooftop raised beds.  The downside?  The specific wood used for this project may not have been sustainably harvested, and it was also extremely expensive.  This is a wood that may be prohibitively expensive for most professional projects, and certainly would exceed the budgets of most at-home installations.

So what is the best material to use for rooftop raised beds?  That’s up for debate.  What do you think?

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standing room only

The packed audience sat in anticipation as I introduced three panelists at the international CitiesAlive  conference on Friday.

The conference, held this year in Philadelphia,  is organized annually by the Toronto-based Green Roof Professional (GRP) accreditation organization Green Roofs for Healthy Cities.  Unlike other international trade conferences, CitiesAlive is unique in its ability to attract a multidisciplinary audience.  The three-day event acted as a magnet for designers, policy makers, scientists, material vendors, rooftop farmers, green roof enthusiasts, and industry leaders.  The diversity was moving, as was each presenter’s ability to capture the interest of these audiences simultaneously.

Out of the conference’s 12 panel discussions, two focused on rooftop agriculture.  The discussion that I was asked to moderate, Design for Food Production and Biodiversity, highlighted built projects that promote either rooftop farming or green roof biodiversity.  While other sessions on green roof policy and key international projects were moderately attended, this panel discussion was filled to the brim, with standing room only.  Rooftop agriculture is one hot topic.

Scott Torrance, Founding Principal of Scott Torrance Landscape Architect Inc, discussed his process of ecological green roof design.  He developed a biodiversity checklist for these rooftop environments, which considers species diversity, nesting habitat, water sources, and other elements that promote wildlife occupation.  Scott’s talk posed interesting questions with regard to the development of pollinator habitat and pollinator corridors on rooftop farms.

Next, Keith Agoada, President of Urban-Ag, energetically described a demonstration greenhouse that he built on top of a nightclub in California.  The structure was designed and erected with a “guerrilla” approach, without the assistance of an architect or waterproofing consultant.  The small greenhouse is visible from an adjacent elevated highway, and is visited regularly by guests and performers from the nightclub below.

Lastly, Anna Suardini, a Technical Sales Coordinator for American Hydrotech, Inc., discussed the Gary Comer Youth Center in Chicago.  This community center houses a 7,400 sf rooftop row farm that is completely enclosed by higher levels of the surrounding building.  The farm is shielded from the elements, and provides children from the surrounding compromised neighborhood with a chance to work with plants and soil in a safe environment.  The rooftop farm’s success quickly lead to the development  of a larger, at-grade farm near the building.  These community agricultural nodes are effectively fostering a positive food production ethic, whereby children and adults alike become reconnected with their food.

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