Cutting The Hole
Run a stud finder across the ceiling and locate the floor joists. Mark the centers of the floor joist with a pencil. Measure the distance between the centers of two floor joists with a pencil. If you have 16 inches between joists, the short end of the hatch must be perpendicular to the joist. If you have 24-inch joists, the short end should run parallel between the joists.
Mark off the length and width of the attic scuttle onto the ceiling with a pencil, using the dimensions given with the attic scuttle. Some scuttles come with a template. Use the template to mark the ceiling.
Cut the ceiling along the tracing with a utility knife. Remove the cut ceiling board from the ceiling. The ceiling board is standard drywall just like your walls.
Installing Into 16-inch Joists
Cut the joist in the center of the opening with a reciprocating saw, cutting 3 1/2-inches over each side of the opening. Remove the cut joist from the opening.
Measure the distance between the two uncut joists with the tape measure. Cut four 2-by-6-inch boards to the measurement with a circular saw.
Set a board on each side with the center face of the board against the end of the cut joist. Place a level across the face of the board to ensure it is straight.
Drive 12d nails through the face of the joists and into the end of the new board with a hammer. Drive nails through the face of the new board and into the end of the cut joist.
Position a second board over the first on each side. Nail the second board to the first and drive nails through the joists and into the ends of the board.
Installing Into 24-inch Joists
Measure between the joists with the tape measure and cut four 2-by-6-inch boards to the measurement with a circular saw.
Place two boards in between the joists at one end of the opening with the front board flush with the opening. Drive 12d nails through the joists and into the ends of the board. Drive four more nails through the face of one board and into the other board.
Repeat the process for the opposite end of the opening. Measure the distance between the two ends before nailing to ensure you have the proper rough frame hole size according to the manufacturers directions.