Abstract: A vertical siding system for an exterior building wall, including vertically oriented panels mounted in flush side-by-side array on supporting structure of the wall and vertically oriented cover members covering the joints between adjacent panels and interlocked with the panels. The cover members have locking flanges along their side edges for insertion in locking grooves formed in side portions of the panels, and are resiliently deformable so that they can be snap-fitted onto the panels after the panels are mounted on the wall. The panels and cover members may be designed to cooperatively simulate the appearance of conventional board-and-batten wooden siding.