How to Replace a Door Jamb

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Replace a Door Jamb
Replace a Door Jamb (Image: Knoll, wwww.thisoldhouse.com, www.rd.com, HGTV)

Whether it's children rough housing, Cujo or someone slamming the door too hard, jambs are broken everyday. As long as your door is not cracked and the door hardware is still functional, you do not have to replace the door itself. Replacing the door jamb is cheap but it is a time consuming process. Read through the steps and be patient with this project.

Things You'll Need

  • Replacement Door Jamb
  • Level
  • Wood Screws
  • Wood Shims
  • Drill
  • Framing Square
  • Wood Putty
  • Paint
  • 3" Screws

In order to access the broken door jamb and remove it, you must carefully "pop" off the existing door trim or casing as it is called in the industry. Use a flat faced pry bar and work it gently into the back seam of the casing where it meets the sheetrock. Work one spot until it is loose, then move several inches down and work another spot. Once enough is loose, you will be able to pull the casing off in one piece with your hands. This will enable you to reinstall it once the jamb is replaced.

This carpenter is doing a fine job of keeping the casing in one piece by working it slowly
This carpenter is doing a fine job of keeping the casing in one piece by working it slowly

With the casing out of your way, use the pry bar and begin to pull the jamb loose in the same manner that your worked the casing. Most older door jambs are nailed in and easy to pry loose, however, all newer homes will have jambs that are screwed in. In this case, just pry the jamb until the paint flakes off and revealsa the screw locations. Use your drill and back out the screws. Importantly, SAVE the side of the jamb which has the hinge locations.

Chances are that you will not be able to walk down to your major homebuilding warehouse and find a jamb that matches your jamb width, length and hinge locations. Don't waste your time here. Go to the pros right away. Nearly all lumber yards offer door and jamb fabrication. They will make you a custom jamb in 24 hours for less than $40. I've done this untold amount of times and always think I'm a genius when I get the jamb and install it, because everything is perfect. I'll show you what dimensions you need to give the lumber shop in the next step.

Let a pro with all the proper milling equipment build your new door jamb
Let a pro with all the proper milling equipment build your new door jamb

In order to get a perfectly fabricated door jamb, provide these dimensions on an 8-1/2 x 11 piece of paper in clear writing. Measure the rough opening of your door opening. Measure the width from stud to stud and the length from the bottom face of the header to the floor. Now, hold the tape against the jamb piece you saved; the one with the hinge locations. Pull the tape from the top of the jamb to the bottom. Note the CENTER LINE measurement of each hinge location; exact middle of the hinge. Note the door strike center line. Transcribe those measurements onto your drawing. Finally, show the swing of the door on your drawing.

Time to run down to the lumber yard and meet with the door guys. Give them your drawing and bring one hinge. Showing them one of the existing hinges will allow them to notch to correct shape into the jamb for the hinges you have.

When you pick up your jamb, it will be in three pieces and taped together. Ask for some wood shims before you head back home. All you need to do when you get home is pop the dowels at the top of the side jambs into the holes routed in the header and the assembly fits together like a lego piece, albeit a flimsy lego piece.

With the jamb assembly in one piece, go ahead and slide it into the rough opening. You'll see up to an 1-1/2" of space between the jamb and the studs of the rough opening, that's normal and intended. Hold the jamb in the opening so that it is flush with the wall. Attach the hinge side first with a couple of screws but don't fasten them all the way in. Take some shims and place them every 12" or so. Take the level and assess the plumbness of the jamb. Adjust the hinges and screw in, checking for plumb as you go.

Attach the other jamb pieces in the same manner. Be sure to check from plumb with your level as you go and use your framing square for the header piece. Again, attach shims every 12". The shims are really important as they keep the door jamb from twisting under the weight and movement of the door.

Install all the hinges to your door. Ok, the pros do the hinges in two parts - they remove the pin and one piece of the hinge is attached to the door and one piece on the jamb - but this takes practice. We're going to do it in one part. With the hinges set on the door, have someone help you get the door into position so that the hinges are matching the hinge notches on the jamb perfectly. Add some shims under the door to help set it just right. Don't screw the hinge into place until it is set correctly. The jamb can't handle a bunch of re-do with the screws.

Use 3
Use 3

Don't be surprised if you door doesn't close perfectly once you have it all assembled. Just go back and fiddle with the jamb screws and shims until the door operates normally.

Completing a door installation is a process of massaging the jambs and not losing your cool
Completing a door installation is a process of massaging the jambs and not losing your cool

Nail back on the trim and repaint. No contractor necessary, nicely done.

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