How to Build an Exterior Door Jamb

Door jambs are made up of four main parts--the header, two legs and the threshold.

The door jamb is the rectangular frame that holds the door. Exterior door jambs are made up of four main parts. The jamb header is the horizontal member directly above the top of the door. The two vertical side members are known as jambs or jamb legs, and the vinyl, wood or metal plate at the bottom of the frame is called a threshold. Most new doors come complete hung in a jamb, but reusing old doors or hanging doors in a custom size may dictate the construction of a new jamb. Use a prefab jamb kit for the project.

Things You'll Need

• Prefab jamb kit
• Tape measure
• Pencil
• Miter saw
• Hammer
• Glue
• Sawhorses
• Nails
• Chisel
• Hinges
• Knob
• Deadbolt
• Drill
• Paddle bit

Instructions

1. Measure your door's height and width, using a tape measure. Most modern doors are 80 inches tall and range from 24 to 36 inches wide.

2. Cut the two jamb legs to length with a miter saw. Each leg will have a notch to accept the ends of the jamb header. Measure from the bottom of that notch to the height of your door, plus the height of your threshold, plus 1/4 inch for clearance, and mark and cut the legs to that height. Mark and cut the jamb header the width of your door, plus 1/2 inch for the notches in the jamb legs and 1/4 inch for clearance.

3. Glue and nail the ends of the jamb header with a hammer into the notches in the jamb legs to create a three-sided rectangular frame. Lay the frame flat on a pair of sawhorses or other sturdy, level work surface.

4. Lay the door flat in the jamb frame 1/8 inch below the bottom face of the jamb header. Mark the top and bottom of each hinge position from the door to the face of the hinge-side jamb. Mark the center of the knob position and the deadbolt lock, if so equipped, on the knob-side jamb. Remove the door from the frame and set it aside.

5. Separate your hinges by driving the blade of screwdriver up through the hinge from the bottom of the pin to drive the pin out through the top. Use a hinge plate as a template and mark its outline on the jamb in each hinge position.

6. Cut the material from each hinge plate outline on the jamb with a hammer and wood chisel to a depth of 1/8 inch. Mark the knob-side jamb even with the center marks for the knob and deadbolt on the inside face of the leg centered between the face of the jamb and the door stop. Bore a 5/8-inch hole with a 1-inch paddle bit in each location.

7. Center a knob striker plate around the knob striker hole in the leg and mark its outline. Cut the material from the outline to a depth of 1/8 inch as for hinge positions. Repeat with the bolt receiver plate for the deadbolt. Attach both plates with ¾-inch wood screws.

8. Attach the second half of each hinge to the corresponding position on the edge of the door. Lay the door back into the frame and align the hinge plates. Drive the pins back into the hinges with a hammer.

9. Cut the threshold to length and attach to the bottom of the jamb legs with treated deck screws, being careful to keep the same distance between the legs from top to bottom.

References

• “Ms. Fix-Its Window and Door Repairs;” Annette L Bach; North Dakota State University; 1974