The gap around a door should be even along all four door edges. If a door has an open gap above its top edge, it will allow air drafts inside and allow interior air to escape. This can waste energy and become costly until you repair it. The cause of the gap could derive from the door's incorrect installation in the frame, or it could be due to the door sagging over time.
Things You'll Need
2-1/2 inch screws
Shut the door. Inspect the clearance along the sides of the door to make sure that the door isn't misaligned.
Extract the middle screw from the top hinge, using a screwdriver or a power drill if the door sags.
Aim a 2-1/2 inch replacement screw slightly downward, and install the screw into the top hinge's middle spot. Use either the screwdriver or power drill, but be sure to fully tighten the screw without over tightening and stripping it.
Tighten the other screws in the top hinge.
Install weatherstripping along the top of the door, if the new hinge screw does not fix the gap. Measure the top jamb, above the door, using a tape measure.
Transfer the jamb measurement to weatherstripping. Cut the weathrstripping to the correct length, using the correct tool for the particular weatherstripping material, such as a hacksaw on foam or metal weatherstripping.
Position the weatherstripping on the top jamb. Secure it to the jamb with brads, using a hammer.