Attach the Stairs
To install the stairs, use two people to hold the staircase in the frame of the trapdoor and have another person go in the attic to attach the stairs.
Up in the attic, slide the joist hangers onto the rods one at a time, placing them at a 45 degree angle to span the frame corners. Then, thread the nuts down but don’t fully tighten them (Image 1).
After all the hangers are in place, make sure there’s an even gap all the way around the frame (Image 2).
Once everything is square, tighten it up (Image 3) and then let go of the staircase down below.