A new Berlin supermarket pairs a rooftop greenhouse with a timber building built to be taken apart and reused, taking a holistic approach to sustainability in retail. Above the produce aisle in Berlin-Lankwitz, lettuce is growing on the roof. REWE opened its new Green Farming market on May 21, capping a timber-framed hall with a 2,760-square-meter glass greenhouse, which the company calls the largest rooftop farm in Germany. Local urban-ag specialist ECF Farmsystems runs the hydroponic operation, which will produce up to 900,000 mixed-salad units per year, harvested daily and distributed to roughly 500 REWE stores across the capital region. Seedling to shelf takes 23 days. Rooftop farms on grocery stores aren't new. What sets REWE's concept apart is the building underneath. The market hall is built from 1,800 cubic meters of domestic softwood, with 72 stacked-timber columns left deliberately exposed across a seven-meter-high space.…