A door sill assembly for use in an external doorway of a building having a novel, flexible, resilient weatherseal strip is disclosed. The weatherseal strip is disposed between a threshold member and an opposing upright side wall of a metal weather cover. A portion of the strip is attached to and covers an exterior facing side portion of the threshold member and contains a flashing or flap depending downwardly from a sloping shoulder which laps over an upper edge portion of the upright side wall. Water falling upon the weatherseal as, for example, due to rainwater dripping from the external face of an overhanging door when in a closed position, will be directed over the sloping shoulder and flashing beyond the upright side wall onto a sloping foot plate of the weather cover, there to gravitate off an exterior end of the weather cover. The weatherseal thus protects underlying wood parts of the door sill assembly from moisture damage without being held in a compressed state.