Can you extend a door jamb?

Yes, it is possible to extend a door jamb to make a doorway wider or taller. There are a few different methods for extending door jambs depending on your needs. The most common reasons to extend a door jamb include widening the doorway, increasing the height for a taller door, or updating the trim around the door. With some basic carpentry skills and the right materials, extending a door jamb is a doable home improvement project.

When Would You Need to Extend a Door Jamb?

Here are some of the most common situations when you may need to extend or alter an existing door jamb:

  • Widening the doorway – If you want to increase the width of a doorway to accommodate larger furniture or improve home accessibility, you’ll need to extend the side jambs outwards to widen the opening.
  • Increasing the height – For taller doors, such as those used in more modern interior design, the door jamb and frame will need to be made taller to accommodate the extra height.
  • Installing casings or moldings – Upgrading or installing new trim like door casings requires both side jambs to be built out to create a nailing surface.
  • Leveling uneven jambs – If a door frame is crooked, the jambs may need to be extended in certain spots to make them plumb and square again.
  • Replacing damaged jambs – Damaged or deteriorating jambs require replacing the original jamb with a new extended jamb.

Knowing exactly why you need to modify the door jamb will inform the details of your jamb extension project.

How to Extend a Wood Door Jamb

For typical wood door jamb extensions, here are the basic steps involved:

  1. Remove door, casing, and stops – Take the door down completely by removing the hinge pins. Take off all the door casing and the door stops in the jamb.
  2. Cut back existing jamb – Make rip cuts to cut off the protruding stops and casing edges of the side jambs. Leave the header and sill alone for now.
  3. Install new jamb extensions – Cut new wood boards to the desired depth you want to extend the jamb. Nail the extensions onto the remains of the old jamb.
  4. Reinstall door stops – Rip thin strips of wood to create new door stops and nail them into the new jamb extensions around the perimeter of the door opening.
  5. Rehang door – Hang the door again by reinserting hinge pins. Make any adjustments to ensure proper clearance.
  6. Install trim casing – Cut new wood casing trim and install around the newly extended jamb. Consider adding brick molding for a finished look.

This process involves basic carpentry techniques like accurate measuring, cutting, nailing, shimming, and adjusting to get a plumb and square door frame opening. Having an assistant can be handy to help position boards and hold alignments when nailing.

How to Extend a Metal Door Jamb

Metal door jamb extensions involve a few different steps:

  1. Remove stops – As with a wood jamb, take off the metal door stops running along the perimeter of the jamb.
  2. Cut back jamb – Use a hacksaw or angle grinder to cut back the side metal jambs close to the wall surface, and cut down any tabs or lips.
  3. Attach metal jamb extensions – Position pre-fabricated metal jamb extensions or fabricated metal plates at the new opening width. Screw into place on the cut back jambs.
  4. Replace stops – Screw new metal door stops into the jamb extensions around the door opening perimeter.
  5. Rehang door – Hang the door to test fit. Make any final adjustments to ensure proper clearances.
  6. Add trim – For metal doors, install new metal moldings or brick molding around the metal jamb extensions.

The process is similar but uses metal cutting tools and screws instead of wood nailing. Precisely measuring and cutting the metal is key to getting a proper fit.

How to Extend an Adjustable Door Jamb

For modern adjustable door jambs:

  1. Remove door stops – Pop off the vinyl door stops in the jambs around the door opening using a pry bar.
  2. Extend adjustable jambs – Loosen screws on the adjustable jamb ends and slide the jambs out to the desired new width. Retighten screws.
  3. Replace door stops – Press the vinyl door stops back into the channel of the extended jambs around the perimeter of the door.
  4. Rehang door – Hang the door again and test the fit. Make final adjustments as needed.
  5. Add new casing – Cut casing trim to fit around the newly extended jambs and install with finishing nails. Paint or stain as desired.

Adjustable door jambs make the extension process much simpler by just sliding out the adjustable portions of the jambs to the new widths.

Tips for Extending Door Jambs

Here are some helpful tips to keep in mind for a successful door jamb extension project:

  • Measure carefully – Accurately measure the new jamb dimensions and opening sizes. Remember to account for trimming off the existing jamb.
  • Check for level and plumb – Use a level and plumb bob to ensure the jamb extensions are perfectly vertical and horizontal.
  • Securely fasten – Attach any jamb extension boards with plenty of nails or screws to create a sturdy frame.
  • Use shims – Use shims between the jamb extensions and framing to fine tune alignments if needed.
  • Match new trim – Choose new brick molding or casing trim that matches or complements the existing trim style.
  • Take your time – Don’t rush through the adjustments and hanging steps. Allow time to get the reveals and clearances right.
  • Seal trims – Caulk and seal the intersections between the jamb extensions and casings to prevent air and moisture intrusion.

Proper preparation, carefully checking alignments, and taking your time are crucial for successfully extending door jambs. But with the right techniques, it is certainly a DIY-friendly project.


Modifying door jambs to make them wider, taller, or to simply upgrade the trim is a relatively straightforward carpentry process. The key steps involve removing existing casing, cutting back the old jamb, installing and aligning new jamb extensions, rehanging the door, and adding new trim casings around the extended jamb.

With accurate measuring, the proper tools, and attention to detail during installation and alignment, you can achieve an excellent finished result. Extending door jamb widths by a few inches or up to a foot is feasible depending on the framing. Follow the techniques for your type of jamb – wood, metal, or adjustable – and take it slow. Door jamb extensions can help refresh the look of your door frames and open up new design possibilities.

Jamb Extension Method Tools Needed Materials Needed
Wood jamb extensions
  • Pry bar
  • Circular saw
  • Miter saw
  • Level
  • Hammer
  • Nail set
  • Wood boards for extensions
  • Wood boards for door stops
  • Finish nails
  • Wood glue
  • Wood shims
  • Casing for trim
Metal jamb extensions
  • Hacksaw or angle grinder
  • Drill
  • Screwdriver
  • Level
  • Metal jamb extension kits
  • Self-tapping screws
  • Metal door stops
  • Metal corner bead
  • Metal molding and brickmold
Adjustable jamb extensions
  • Pry bar
  • Miter saw
  • Level
  • Replacement vinyl door stops
  • Casing trim
  • Finish nails