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Replacing an existing door with a new one is just about as easy as it sounds—you use the old door as a template to cut the new door to size and to outfit it with hinges and a lockset. Then you replace it in the existing jamb. No fuss, no muss.

Switching out the door in an old jamb is a great solution when you have a door that's badly warped or damaged, or when you want to upgrade all the doors in your home to improve quality or change style. We asked Tom Silva, This Old House general contractor, to take us through the steps. He's hung and replaced so many doors he's lost track of the number. As a result, he's got a few tricks to maek things go faster and better.

Step 1

Interior Door Overview

Illustration by Gregory Nemec

Before you begin, measure the width and height of the old door (the thickness of all but the oldest interior passage doors is standardized at 1 ⅜ inches). Bring these dimensions with you when you buy the new door "blank"—unlike a "prehung" door, it won't be surrounded by a jamb or drilled out for the lockset. Doors come in just a few heights—80 inches is the standard—but a wide range of standard widths.

CAUTION: Door manufacturers use shorthand to describe a door's width. So a 3-0 (pronounced "three-oh") door is 3 feet, 0 inches, or 36 inches, wide—not 30 inches.

Step 2

Remove the Old Door

Photo by Brian Wilder

Stand on the hinge side of the door and remove the pins from the hinges. Always start at the bottom hinge and work up so the door doesn't topple over onto you.

If a pin won't come out by hand, gently tap it out with a hammer and screwdriver.

Have a helper support the door as you begin to remove the top pin.

Tip: To avoid losing the pins, drop them back into the hinge leaves on the doorjamb.

Step 3

Mark the New Door for Trimming

Photo by Brian Wilder

Remove the lockset (doorknob) and hinges from the old door. If reusing the lockset, note how it goes together.

Lay the new door across a pair of sawhorses and set the old door on top, aligning the top end and the lockset edge of the old door perfectly flush with the new door.

Trace around the old door with a pencil to indicate where the new door must be trimmed down to size.

Tip: Correct clearance for an installed interior door is 1/8 inch on the sides and top (to jamb) and 5/8 inch at the bottom (to flooring/carpet).

Step 4

Cut the Door down to Size

Photo by Brian Wilder

Score the pencil marks on the new door with a sharp utility knife and straightedge to help prevent the wood from splintering when you cut it with a circular saw.

Cut the door to the correct height using a straightedge guide and a circular saw. If you need to remove more than 1 inch, take half off the bottom of the door and half off the top.

Trim the door to width in the same manner.

Tip: If removing less than 3/16 inch, use a hand plane instead of a circular saw.

Step 5

Lay out the Hinge Mortises

Photo by Brian Wilder

Lay the old door back on top of the new door, aligning them so that all four edges are flush.

Line up a combination square with the old door's hinge mortises and transfer their locations to the new door.

Tip: Mark the cut lines for the mortises with a utility knife; it produces a much more precise line than a pencil.

Step 6

Chisel out for the Hinges

Photo by Brian Wilder

Lay a protective pad on the floor and stand the new door on edge, with the hinge layouts facing up.

Next, chisel out for the hinges (these are called hinge mortises). Hold the chisel vertically and tap it with a hammer to outline the mortise. Then make a series of closely spaced cuts as deep as the thickness of the hinge.

Next, hold the chisel at a low angle with its beveled face flat against the wood to prevent it from digging in too deeply when completing the mortise.

Lightly tap the chisel with the hammer to chip away the waste wood a little bit at a time.

Step 7

Screw on the Hinges

Photo by Brian Wilder

Check the depth of the hinge mortises by test-fitting a hinge leaf; it should be flush with the door edge. If necessary, use the chisel to pare away a bit more wood.

Set the hinge leaf into the mortise. Use a drill and centering bit to bore pilot holes through the screw holes.

Screw the hinge to the door.

Test-fit the door in the opening. Check that it closes without binding and that there's proper clearance (1/8 inch) between the door and frame. If not, plane the edges.

Tip: If you accidentally cut a mortise too deep, slip a thin wood or cardboard shim behind the hinge leaf.

Step 8

Drill for and Assemble the Lockset

Photo by Brian Wilder

Mark where the strike-plate hole meets the door edge.

Position the template supplied with the lockset on this mark and mark for the doorknob and latch. If reusing the old lockset, take measurements from the old door.

Drill the doorknob face bore with a 2 1/8-inch hole saw. Cut the latch's edge bore with a 7/8-inch spade bit.

Paint or stain the door, as desired, and let dry.

Insert the latch assembly into the edge bore and trace around it with a utility knife. Chisel out a shallow mortise inside this outline.

Screw the latch to the door, then install the doorknobs.

Step 9

Hang the New Door

Photo by Brian Wilder

Hold the door in the opening and interlace the hinge knuckles.

Once all the hinges are aligned, have a helper insert the hinge pins.

Test the door, making sure it swings smoothly and that the latch engages the strike plate on the doorjamb. If necessary, reposition the strike plate.

Tip: If the door rattles when closed, slightly bend out the metal tab that's located inside of the strike plate.