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With the joists braced, proceed to cut the identified joist. Use a circular saw to cut most of the way through the joist, then switch to a smaller hand saw (like a box saw) to finish the cut carefully without damaging the drywall below. After removing the cut section of the joist, install two new pieces of lumber as headers, running perpendicular to the existing joists, at the front and back of the new opening. Secure these headers to the existing joists using double joist hangers and appropriate load-rated fasteners (e.g., nails or structural screws driven with a nail gun or hammer). This creates a framed opening for the attic stair. The space needed for the attic stair unit will typically be 22.5 inches wide, requiring the installation of an additional joist parallel to the original joist, held by single joist hangers at either end.