Abstract: A door sill-to-jamb kit manufactured from rot-resistant thermoplastic material is placed between a bottom of a side jamb and a sill of a door frame assembly. Parallel tenons fitting into mortises at the base of the side jamb and fasteners secure the door sill-to-jamb kit to the side jamb as well as to the door sill. Elevated height of the side jamb prevents contact with moisture on the surface of door sill and between the door sill-to-jamb kit and the door sill, thus reducing a risk of rotting of the wooden side jamb.