Over time, the door frames in your home may become damaged. Rot is one type of damage that can occur. It not only can make your home look shabby, but rot in an exterior door frame also can cause drafts and allow water to leak in. Rot can spread, so damage that begins in one small area of a door frame can end up damaging the entire frame. In many cases, you can repair the door frame yourself and prevent bigger, more costly problems.
Scrape away the rotten wood with a chisel. Inspect the door frame to see how far the rot has spread.
Cut around the edges of the door trim with a reciprocating saw. Pry the trim up with a shim to make it easier to cut through the nails holding the trim to the door frame.
Cut through the paint on the inside of the door casing with a utility knife. The casing is the decorative moulding around the perimeter of the door frame.
Pry the door jamb -- the vertical board running up the side of the door -- away from the jamb extension with a pry bar. The extension is the wood next to the door jamb. Cut through the nails with the reciprocating saw.
Cut through the jamb extension along the floor, using the reciprocating saw.
Cut through the jamb extension above the rot-damaged area. Dry the wood around the rotted area with a hair dryer or heat gun.
Measure the space from the cut you made to the floor. Cut a section of jamb moulding with a saw to fit the space. Attach the jamb moulding to the door frame with galvanised screws and a screwdriver.
Measure and cut the wood for the door jamb. Screw it to the jamb extension with galvanised screws.
Nail the door casings back into position.
Fill the gaps with caulk to prevent water from leaking through.
Add two coats of primer and a top coat of paint to the new wood.
If the damaged area consists of nicks or small cracks, you may be able to just patch the affected area or fill it with wood putty.
If the damage to the door frame is caused by rot, you must remove all of the damaged wood to prevent the rot from spreading.