Install door casing

Tools and Materials

  • 3 lengths of casing (2 for the uprights and 1 for the horizontal head section)
  • miter saw
  • hammer
  • nail set
  • finish nails

Step 1: Attach the first upright

The casing’s margin (the inner edge to the edge of the door jamb) should be 1/5″ to 2/5″. Mark off the margin position around the edge of the door jamb. Join the marks at the corners to have a right-angled guide line. At the head, mark the piece where it meets the right-angled margin mark. Make a mitered cut, using the marked-off point to guide you. Reposition the casing, with its inner corner at the apex of the margin’s right angle. Attach it with three nails at the top.

Step 2: Cut the head section

Make a mitered cut on the head section to join with the section already fitted on the jamb. Hold the head section in position while marking off the cut for the other miter on the right-hand end of the length. Cut the miter.

Step 3: Cut the other upright

Place the right-hand upright section of casing to mark off in relation to the margin requirement and cut this miter. Nail the right-hand upright in place securely at the top.

Step 4: Attach the casing

  • Check that the head length of casing fits and nail it into position.
  • Drive in nails along the entire lengths of casing.
  • Use a nail set to drive all nails below the surface.
  • To keep mitered corners tight, you will need nails through both pieces by drilling pilot holes.
  • Drive a 1″ finish nail into each pilot hole on the mitered corners. Then fill nail holes and sand smooth, if necessary.


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