that is one hot potato.

To the newbie, designing and building a rooftop farm may seem like a cakewalk.  What’s the big deal?  You just plop a regular farm on top of a building and it’s business as usual, right?  Wrong.  Planning a successful rooftop farm requires careful consideration of siting (where the farm will be located), infrastructure, project goals, and long-term financing.  Coordination with the building’s architect is also crucial, particularly when designing a rooftop farm for a building that has not yet been built.

Proper coordination can avoid one serious rooftop threat that ground-level farmers will never face: reflectivity.  Light that reflects off of surrounding surfaces can scorch spinach and burn brassicas.  Highly reflective glass on neighboring buildings, or even on surrounding levels of the farm’s own building, can devastate crops.

Here are two anecdotes that illustrate the power of reflectivity:

1|  The green roof firm for which I work designed and built a courtyard shade garden for an important Philadelphia client.  The courtyard is surrounded by taller building stories, which are faced with glass so that workers can enjoy the garden view.  The garden’s ferns, heuchera, and other shade plants performed well at first, until strong summer rays reflected off of the windows and fried some of the plants!  What seemed at first to be a shaded haven had become a seasonal hotbox.  The most sensitive plants were replaced with sun-loving species, and next time we will coordinate with the architect to avoid a similar mishap.

2|  In 2010 a Las Vegas hotel found itself in a sticky situation when poolside guests were burned by light reflecting off of the hotel’s glass façade.  For 90 minutes each day, the concave building reflects light that is hot enough to melt plastic and burn hair.  Guests have the ability to seek refuge under patio umbrellas, but replace people with vegetable plants, and you’d have some fried green tomatoes on your hands.

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