Title pretty much says it all, but here is a picture just in case:

enter image description here

I think it has to do with the wall achors but I can't find a definitive answer.

Just to clarify: steel frames for masonry walls only have a single return/backend.

  • 1
    Stiffness. It stops those sections from bending and leaving gaps between that & the wall.
    – brhans
    Jul 19, 2016 at 13:18
  • As isherwood wrote in his answer - waviness is a better description than bending.
    – brhans
    Jul 19, 2016 at 14:33
  • 1
    There are clips that use that edge to hold the bottom of the door. as well as the door is majorly held in place with caulk around the perimeter, or at least it should be. It also keeps the otherwise thin edge from cutting into the drywall because of the opening and closing of the door will eventually erode the paper then of coarse the jamb would loosen,.
    – Jack
    Jul 19, 2016 at 16:49

1 Answer 1


Stiffness is one reason, but not exactly in the way that was mentioned above. That return will prevent waviness as viewed from the room.

Also, raw edges are ugly, even if they return into the wall. They're difficult to caulk, too, as there's no real bond surface--the caulk just falls behind if there's a gap.

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