A header joist runs perpendicular to all the common joists that form a floor system and caps the open end. Also known as a band board or rim joist, header joists stabilize the common joists and prevent them from rolling or tipping. They are attached to the floor system with three nails driven through the header joist and into each one of the common joist ends.
Mark the starting point of one side of the stairs onto the header joist.
Mark the locations of each stringer onto the header joist. Using your tape measure and a pencil, place tic marks every 12 to 16 inches beyond your starting point to the width of your stairs (36 inches minimum). Consult your local permit office for stringer spacing requirements in your area.
Align your carpenter square with each tic mark and draw a line using the square as a guide.
Align the stringer with a mark and tack it into place with a galvanized framing nail.
Slide a slopable stair connector (available at most hardware stores and lumber yards) onto the header joist alongside the stringer and nail it in place using galvanized hanger nails. Allow the bottom half of the hanger to hang below the header joist.
Bend the bottom half of the hanger up until it rests snugly against the bottom of the stringer and nail in place using galvanized hanger nails.
Repeat steps 4 through 6 for each stringer.