_{This may be simple and fairly well known, but I couldn't find it anywhere here, and felt it deserved a place in the ranks of puzzles}

A man is found dead, hanging in an empty barn having committed suicide. The base of the barn was 20 feet by 30 feet, and the ceiling was 10 feet above the ground. The rope was 4 feet from the roof to the man's neck, and the man's feet were hanging 1 foot above the ground, and the man was 5 feet from where the rope was around his neck to his toes. The man was hanging from the exact center of the barn. Aside from the man and the rope, there were no other objects in the barn. The ladder used to tie the rope up was found outside around the corner (guess he didn't want those that found him to have to move it later). There were no supports or beams along the ceiling of the barn.

It was determined that the man was too weak to jump and pull himself into the noose, or to climb onto the roof with just his hands. How did he manage to hang himself?

Edit: The door to the barn was closed and locked from the inside, so no one had come in or out since the deed was done. The barn was structurally sound, with no holes or windows to be found anywhere. The roof was also water tight.