rooftop rice paddy

Two hectares of rooftop in South Central China’s Guangxi Zhuang Autonomous Region stand a cut above the rest.  The Liuzhou Chenfeng Brewing Factory, founded in 1954, supports one of China’s only rooftop rice paddies.  Tan Zhaohan, the factory’s head rice planter, reported to David Cao of Bejing Impact that the roofs were first planted in 2010.  Rice, lotus and vegetables flourish on the roof while other crops are grown on the property at ground-level.

According to Zhaohan, the brewery’s owner developed this agricultural rooftop vision and took the necessary steps to enhance each roof area’s waterproofing membrane.  This process likely involved either patching and testing the existing membrane for water tightness (i.e. leaks) or applying a new membrane altogether.  Water pumped from underground is ponded on the roof thanks to six drains on each roof with adjustable collars.  The collars allow workers to adjust the rice paddy’s water level depending on crop needs.

Ponding water on rooftops is a common practice today in cities like New York, where local stormwater regulations incentivize a reduction in peak delay.  Allow me to explain.  During a rain event or snow melt event, water hits roofs, streets and other impervious surfaces and rushes to the storm sewer, often overloading the system.  When we’re able to delay the rate at which water flows to the sewer after such an event, that’s called reducing the peak delay.   On rooftops this delay can be achieved through green infrastructure such as green roofs, or by ponding water for 24 hours within a blue roof.  Another type of rooftop ponding, common in Germany, involves ponding 1″-2″ of water at the base of a green roof to provide base-level irrigation water to the plants.  A third example of rooftop ponding has been articulated by historian Geoff Wilson, who believes that the Hanging Gardens of Babylon (in present-day Iraq) may have supported rooftop aquaculture, or fish farming, for the building’s residents.

While rooftop ponding is clearly nothing new,  its use for growing commercial grain and vegetables is astounding.  I must admit that I’ve been asked about the feasibility of growing rice on rooftops several times throughout the years, and have brushed off the question as an impossibility each time.  After recently learning of the Liuzhou Chenfeng Brewing Factory roof, though, I am shamed!  Cultivating rooftop rice is indeed feasible given proper growing and architectural conditions.

Why build a rooftop rice paddy, you ask?  The benefits are twofold.  First, the rooftop farm provides fresh, in-house produce to the brewery below for beer making, wine making and other uses.  This on-site production may result in monetary savings to the brewery because the business would need to buy fewer ingredients.  Given the size of the roof areas, though, it’s likely that most ingredients are still purchased from producers or suppliers.

Secondly, the brewery’s manager, Liu Xinsheng, reported to Bejing Impact that the rooftop farm helps to moderate the buildings’ indoor temperature, thereby saving the company money on utility bills.  This makes sense, because water holds heat longer than a bare membrane roof.  As outdoor temperatures fluctuate, the water within Liuzhou Chenfeng Brewing Factory’s rice paddies remains relatively constant.  During the heat of day the paddies reduce the need for indoor air conditioning.  Additionally, the brewery is only one story tall, which furthers the ability of the rooftop farm to keep the building cool.  Temperature control via green roofs and blue roofs is a function of the area of the roof relative to the volume of the building, which means that low (1-2 story) buildings reap the largest temperature benefits.

The potential for cultivating rooftops for culturally-relevant crops is expanding, thanks to rooftop farms such as that atop the Liuzhou Chenfeng Brewing Factory.  Let’s wait and see what impossibilities become possible around the world as creative thinkers transform their rooftop acreage.