A drainable louver comprises a frame composed of a sill, a head and a pair of side members forming a rectangular opening and a multiplicity of vertically spaced-apart louver blades extending across the opening between the side members and fastened to the side members. Each of the blades has a drainage trough extending along its lower front edge and terminating at each end adjacent a corresponding side member of the frame, and each of the side frame members has a base wall portion engaging the corresponding ends of the blades throughout their lateral extent. Each side member has a front flange portion defining with a front part of the base wall portion a vertical drainage channel located laterally of the corresponding ends of the drainage troughs of the louver blades on the side of the base wall portion opposite from the blade. The drainage channel of each side member has an opening at the front face of the frame throughout its vertical extent, and the front part of the base wall portion has an opening in register with the corresponding end of the drainage trough of each louver blade so that water can flow from the drainage trough of each blade into the drainage channel.