An extrudable keder rail and a clamping anchor for the keder rail are cooperative to secure keder fabric to a building support beam. The clamping anchor allows the keder rail to be securely attached to a standard beam without drilling holes or strapping about the beam. A temporary clamp and movable tensioning device allow the keder rails and keder fabric to be applied to the building support beams after the support beams have been assembled and installed.