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What This Guide Covers #
Install basic mitered casing on one face of an interior door jamb in new construction. The same casing method finishes a wood-jamb cased opening; build and set that jamb first using How to Install a Cased Opening. Repeat this procedure on the other face when both faces are in scope. Decorative headers are a separate style.
Before You Begin #
- Confirm the door jamb is installed correctly, or the cased-opening jamb is level, plumb, straight and square. A cased opening still has a wood jamb to reference.
- Drywall must be ready; confirm the casing profile and the finished floor elevation. If flooring is not installed, use its known elevation when fitting the casing legs.
Tools and Materials #
- Miter saw, tape measure, pencil, small adjustable combination square, 18-gauge brad nailer, 1-3/4-inch brads and a nail set. Include a compressor and hose for a pneumatic nailer.
- Approved casing stock, wood glue, wood putty and sanding supplies.
Installation Steps #
Step 1. Lay Out the Reveal and Fit the Head #
Set the combination square to 3/16 inch and mark the reveal on the head and both jamb legs. Measure the head casing between the side reveal marks at the short points of its miters. Cut the two top corner miters, starting with 45-degree cuts for a square opening, and dry-fit against the reveal marks. Check the fit with the side pieces before final fastening.
Step 2. Fit the Side Pieces and Glue the Miters #
Measure each leg from its intended bottom elevation to the short point of the top miter. Cut and dry-fit each piece against the head. Keep the same 3/16-inch reveal down the jamb and fit the miters tight and flush. Adjust a cut that does not close rather than forcing the joint together or hiding a gap with putty. Apply wood glue liberally to both mating miter faces, bring the joint together and hold it tight until the glue grabs. Wipe off the squeeze-out.
Step 3. Fasten and Finish the Joints #
Fasten the head and side casing with 18-gauge 1-3/4-inch brads, keeping the reveal aligned with the jamb. Keep checking the miters as you fasten. Do not cross-nail the miters. Casing follows the jamb reveal; do not move it away from that layout just to make an individual piece read level or plumb.
For paint-grade work, keep the casing seated cleanly against the jamb. It can angle back from a slightly proud jamb toward thinner drywall. Do not bow the casing by forcing it into every wall hollow; the painter handles the outside caulk line. Confirm a separate fitting detail for stain-grade work.
Set any proud brads below the surface. Putty and sand the wood joints as part of our carpentry work. Nail-hole filling, outside caulking, painting and staining belong to the painter. Collect cutoffs and sweep.
QC / Punch Checklist #
Check the even 3/16-inch reveal, tight glued miters, flush joint faces, puttied and sanded wood joints, and set fasteners. Check the fit at the finished floor elevation and leave the area clean.
Common Mistakes #
- Uneven reveal: check the casing layout and fit before assuming the jamb needs to come out.
- Open miter: check both cuts and their fit, re-cut when needed, then glue and close the joint. Putty is for finishing a fitted joint.
- Wavy casing: avoid pulling it into uneven drywall. Maintain its clean seat on the jamb.
Related Guides #
Reference Photos #
The following photos show examples of this type of work completed in the field. These serve as visual references for quality standards, proper installation techniques, and finished results.
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