Assemble the frame of the Bilco basement doors according to manufacturer instructions for the model you are using. Set the doorframe in place over the opening of the basement stairwell and mark the holes that you need to drill using a marker. Remove the frame from the opening and drill all necessary holes using a drill and masonry bit.
Apply a layer of caulk at the header and along the sides of the Bilco basement doorframe. Set the unit in place over the opening to the basement stairwell. Secure the frame to the opening using a socket, ratchet and concrete bolts.
Install the doors on the doorframe using a flat-tip screwdriver, round-head screws and nuts. Lubricate the plastic parts on the torsion rods with the silicone grease that comes with the doors. The torsion rods look like long bars with hooks at the ends.
Insert the hooked end of a rod into the upper hinge of the left door. Push the L-shaped end of the rod down into its retaining ring. Repeat the procedure for the lower torsion rod on the left side. Insert the hooked end of the rod into the right hinge in the same manner and repeat the process.
Apply a layer of caulk around the edges of the doorframe where it meets the wall, and along the side to help prevent water from getting into the stairwell. Apply a coat of outdoor paint to the Bilco basement door once the project is complete, if you are using a steel model. Do not use oil-based wood paint on the door.