Does the existing door sill need to be removed along with the door jamb? From the existing door sill to the top of the jamb it measures 80 inches. After the jamb is removed, it'll most likele be 81 or more inches. Does the new prehung door sit on top of the old sill?
Thanks, Joe.

 

Exterior prehungs generally include a new sill already mounted to the jamb.

 

If you have an old sloped door sill on your old door, yes, you usually want to remove it and replace it with something flat and level. In a few cases, you might be able to cut a filler piece and set set on top of the old sloped sill to give the new door a flat, level surface to sit on, but its rare to not tear the entire old jamb and sill out when replacing an exterior prehung door. It's just that you will have some rebuilding to do to get the opening ready for the new door.

New prehung doors usually will work best in the opening if the rough sill that they sit on is about 1/2" below the level of the finished floor.

 

THANK YOU VERY VERY MUCH, that was the information I was looking for.
Have a great day,
joe