The invention relates to a drop-down seal for a building part comprising a housing (1), a sealing strip (2, 3) that can be raised and lowered in said housing (1), and a spring-loaded lowering mechanism (8), which causes automatic lowering of the sealing strip (2, 3) when the building part is closed. The lowering mechanism (8) is connected to a slide (4, 6), which protrudes beyond the housing (1) at one end and which activates the lowering mechanism (8) when the building part is closed. The slide (4, 5) applies a tension to the lowering mechanism (8). The drop-down seal according to the invention enables a one-sided triggering in tension, wherein the seal has a space-saving design.