Some tips for installing exterior French doors include using pre-hung French doors, preparing the installation area prior to fixing the door, using wooden boards to conceal the extra space, and positioning the door correctly in the opening. Also, place insulation on the door's sides and caulk the outer edges, and attach the door hardware appropriately.
Pre-hung French doors make installation easy as they come with the frame and holes for the door knob, hinges and locks. To prepare the installation area, first take out the existing door, and apply caulk on thoroughly the area. Allow the caulk to dry before fixing the door.
Use 2-by-4 wooden boards to cover the extra space in the door opening. To position the French door correctly, take someone's assistance, place it in an upright position, and slide the bottom edge of the door in the threshold. If required, tap the door's top edge gently to make it fit in the opening. Shim the jambs to make them level. Install the door temporarily using nails, and ensure that it is level using a level.
Use 100 percent silicone caulk to make the door waterproof, and apply it on the outer edges of the door as well as on the insulation. After installing the door, check to see if it functions smoothly.
Attach the deadbolt and door knob to the door that is to be used as the passage one. Affix a dummy knob, plates that receive the deadbolt and the striker on the other door.