How to Build a Door Jamb

How to Build a Door Jamb

The steps below will outline how to build a custom door jamb to fit an existing door.

1. Find Door Jamb Measurements

   Measure the height and width of the door and record the measurements. To find the width of the jamb, add 1/4 inch to the width of the door. For the height, add 5/8-inch, or slightly more if using a thicker flooring material like carpet.

2. Check the Floor for Level

   Place a 4-foot level on the floor spanning the bottom of the door frame. If the floor is out of level, lift the level on the end that is lower until it reads level. Use a measuring tape to measure the gap between the level and the floor to find out far out of level the side is.

3. Adjust Side Jamb Measurement

   If your floor was out of level, add the recorded measurement from step two to the height of the side jamb that will be placed on the longer side.

4. Cut the Side Jambs to Length

   Cut the side jambs to length using a miter saw. Remember to account for the height of the door, the additional 5/8 inch, and the additional length to account for an out-of-level floor.

   Tip

   To help keep track of the side jambs as you work, label them as "hinge jamb" and "latch jamb." This is especially helpful when working with side jambs that are different lengths.

5. Mount Hinges on Door

   Split the hinges by pulling the pins and mounting the door sides on the door.

6. Mock Up the Side Jambs

   Place the side jambs on each side of the door. For spacing, make sure the door is flush with the edges of the jambs, then slide the jambs until 1/8 inch sticks out at the top of the door. Clamp the jambs in place.

7. Mark the Hinge Height Location

   Mark the location of each hinge on the jamb with a pencil.

8. Mark the Hinge Leaf Depth

   Matching the hinge leaf's depth on the door jamb with that of the door is crucial to the door's operation once mounted. To transfer the depth, follow this procedure:

   1. Hold a combination square up to the edge of the door on the side where the hinge protrudes from the door.
   2. Adjust the combination square until it reaches the edge of the hinge leaf.
   3. Lock the combination square.
   4. Place the combination square on the hinge jamb where you marked the hinge height position.
   5. Use a pencil to mark the depth of the hinge leaf on the jamb.

9. Find the Hinge Mortise Depth

   Use a combination square to measure the thickness of the hinge to find the mortise depth, then set your router to match this depth.

10. Mortise the Jamb

    Carefully mortise the jamb inside the marked hinge locations using a router. Get as close as you can to the outline of the hinge with the router, then clean the rest of the material out using a chisel.

    Tip

    There are several hinge mortising jigs available that may be helpful. However, these aren't always applicable for custom jobs.

11. Mount the Door

    Screw the hinges into the jamb, then slide the door side in place. Hammer the pin into the hinges to tie the two sides together.

12. Cut and Mount the Head Jamb

    Cut the head jamb to the door's width plus 1/4 inch. Place it on top of the side jambs and nail through the head jamb into the ends of the side jambs using 3-inch finish nails. To lower the chances of the wood splitting or the nail getting off track, you can pre-drill the nail holes.

13. Mount the Door Jamb

    With the door mounted in the jamb, place the jamb inside the door frame. Shim the sides and top to ensure it is plumb and level and that the gap between the door and the jamb is equal on the top and sides. Once adjusted, mount the jamb within the frame.

14. Mount Door Stops

    Now that the door jamb and door are mounted in the door frame, add the door stops. Cut the top stop to match the inside width of the door jamb. Place it against the top of the door with the flat side facing the door and mount it in place with finish nails. Repeat the cutting and mounting process on the side jambs.