According to the pilot, fog approached the airport from the south, as he approached from the north at the conclusion of a local flight. His approach to landing was “normal,” but in the flare the airplane floated longer than anticipated. At touchdown, the pilot applied “heavy braking” before the airplane overran the departure end of the runway, struck a fence, a tree, and substantially damaged the left wing. The pilot was unable to estimate the airplane’s speed on approach or its point of touchdown on the runway. The pilot stated that there were no mechanical deficiencies with the airplane, and added that he did not abort the landing due to the approaching fog.