I'm restoring an old house and one of the problems I'm facing is a couple of doors that have become out of square. Over the years gravity has pulled down the non-hinged side as much as an inch or more leaving a gap at the top of the frame and dragging the threshold at the bottom. What's worse is the doors feature a large window about 27" x 38" and to cut the glass to fit the opening I have to cut a parallelogram instead of a rectangle.

My question is this: are there any tricks to realigning such sagging doors. Do I just pound it back to square with a mallet and then reglue?

 

Glue it up and use an 8' bar clamp to squeeze the door diagonally, bringing the long corners together. Have the glass out when you do this, and measure from corner to corner both ways to ensure you have it square.

 

Would it help to drive screws at each of the four corners or would that interfere with the wood movement?

 

It would be a bad idea to insert any screws until the door has been squared up.

 

That's what I meant.

I'm afraid I won't get a good glue up unless I knock the rails and stiles apart, so I was considering four long screws that went through the stiles and into the top and bottom rail just to give it a little more stability.

I just recall being advised against screwing doors together because of the seasonal wood movement.

 

I would regard the door as a gamble at best.

I would try to loosen as many pieces as I safely could by rocking back at forth. Then I would carefully clean up the mortise and tenon joints without removing any stock. Then I would glue what I could and reassemble as xsleeper described.

It is likely that only the hinge side needs the glue and straightening, so don't mess with the latch side unless you have to.