Help. My wife found on old barn door to put in our house to replace an exterior door. The new door is narrower and longer than the pre-hung door it is replacing. I need to know what to do to install it sometime this summer.

 

You might want to think about it before you make the doorway narrower. Would this be a problem if you had to replace the refrigerator or the couch at some point?

Making the doorway narrower is pretty simple. Remove the present door and its jamb, add a 2X4 and a little piece of bottom plate as needed to make the rough opening 2" wider that the door itself, and install a new jamb. You may be able to add to both sides equally and simply use wider casings.

Cutting the door to the height of your present door (probably 80") would be much smarter (and simpler!!) than trying to make the rough opening taller. Raising the header is MAJOR surgery!!