How to Make a Door Frame Smaller

Written by Chris Deziel; Updated December 27, 2018

Discovering that a door is too short or narrow for the opening in which you want to hang it may be an "uh-oh" moment, but it isn't a major problem. Assuming you don't want to modify the door, making the opening smaller is usually only a matter of furring out the jamb. The procedure is straightforward if the dimensional difference between the door and the frame is less than an inch. If the difference is more than that, you may have to decide between replacing the door casing with wider material or adding new drywall around the door frame.

  1. Calculate the difference in dimensions between the door and the frame. If the difference is less than 1 inch, you only need to fur out one side of the frame. If it's more than that, you may be able to reuse the door casing by furring out both sides. If the door is too short, you'll need to lower the top jamb by an appropriate amount.

  2. Pry off the door casing and the knob-side and top jambs with a pry bar if you only need to fur out one side of the frame. If you're narrowing the frame by more than an inch, remove the hinge-side jamb as well. To make the frame shorter, pry off the entire jamb. Remove the shims from behind the jamb pieces you've pried off and discard them.

  3. Rip furring strips from 2-by-4-inch lumber on a table saw, cutting the strips along the width of the lumber, not the edge. You will have to extend the saw blade to its full height to do this, and you should use a sharp blade.

  4. Cut the strips to the full length of the framing on which you plan to attach them. When determining how thick to make them, don't forget to allow for a 1/2-inch gap on either side of the door and a similar gap between the top of the door and the jamb. You should also allow for a 1/2- to 3/4-inch clearance between the bottom of the door and the floor.

  5. Attach the furring strips to the framing with wood screws long enough to bite at least an inch into the framing. Drill pilot holes in the strips with a 1/4-inch drill bit before driving screws into them to avoid splitting the wood.

  6. Cut the jamb pieces with a circular saw to fit the new opening. If you've narrowed the opening, cut the top jamb and rabbet the end you cut with a router and a 1/2-inch rabbeting bit. If you've shortened the opening, cut off the bottoms off the side jambs so they'll fit inside it.

  7. Attach the jamb pieces that you removed, using new shims and a 4-foot level to plumb them. Tap the shims together from opposite sides of the jamb so that they meet in the middle. Drive 2-inch finish nails through the jamb and the shims to make sure the shims stay in place. Cut off the ends of the shims with a handsaw.

  8. Nail off the jambs with pairs of 2-inch finish nails spaced approximately 10 to 12 inches apart. Sink the heads of the nails with a nail punch.

  9. Install the casing. If you narrowed the opening by less than an inch, the old casing will probably work. Cut an amount off the top casing equal to the amount by which you narrowed the frame, then fit the side casing over the gap between the jamb and the wallboard. If you shortened the opening, cut the bottoms off the side casing.

  10. Use wider trim or modify the wall if the old casing no longer works. You may be able to find suitable trim at your local lumberyard, but if not, make your own with a table saw. If you choose to modify the wall, attach strips of drywall where needed to cover the furring strips, then tape and finish the drywall. After making this modification, you can reuse the old casing.

  11. Things You Will Need

    • Pry bar

    • 2-by-4-inch lumber

    • Table saw

    • Wood screws

    • Drill

    • 1/4-inch drill bit

    • No. 2 Phillips bit

    • Circular saw

    • Router

    • 1/2-inch rabbeting bit

    • Shims

    • 4-foot level

    • 2-inch finish nails

    • Hammer

    • Handsaw

    • Nail punch

    • Wide trim

    • Drywall strips

    • Drywall finishing supplies


    If you need to change the dimensions of the opening by more than 6 inches, reframing it is probably a better option than adding furring strips.

    The International Residential Code specifies a minimum width of 36 inches and a minimum height of 80 inches for the main exit door of a house. Other interior and exterior passage doors can be narrower but should comply with the height requirement. Doors leading to storage areas can be any size.

About the Author

Chris Deziel


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