[header] How to adjust a sagging door [title] Find the sagging door's cause. [step] Inspect the door from inside, or the side from where you can see the hinges. Locate the gaps and where the door is tight. 
It's common in sagging doors for the hinge side at the bottom to be tighter against the frame. The opposite side, or strike side, is often gapped at the top and tight where the door meets the sill.