Re: Attic Ladder for Very Tight Openning
check with a local lumberyard, they usually have several different attic hatch ladder kits, see what sizes they have.
sounding by the 21" the framers probably goofed on the layout of the trusses, when setting them they prob put one truss on the wrong side of the line which made the spacing 1 1/2" smaller, it should be 22 1/2
your only other option would be to go up in the attci clear away a section of insulation then cut out a new opening in the ceiling for a proper hatch
fire up the saw and make some dust