Window casing is the finish trim that covers the joint between the window frame (or jamb extension) and the surrounding drywall or plaster. On the interior, it serves both a functional purpose (hiding the rough gap at the frame edge and any shims) and an aesthetic one (providing a finished, architectural appearance that ties the window to the room’s trim style). Exterior casing serves similar roles outside, where it also provides a substrate for caulking at the siding joint.
Casing Profiles
Casing profiles run from simple to elaborate:
- Flat (modern) — simple rectangular profile; 2½–3½ inches wide; minimal shadow line; suits contemporary and craftsman interiors
- Colonial — slightly profiled edge with a flat face; the most common stock profile in American homes
- Ogee / traditional — S-curve profile with pronounced shadow line; traditional and Victorian styles
- Craftsman — wide flat boards with a small backband edge; Arts and Crafts and bungalow styles
Interior Casing Components
- Head casing — horizontal piece across the top
- Side casings (legs) — vertical pieces on each side
- Stool — the flat horizontal shelf piece at the bottom (often incorrectly called the sill)
- Apron — the trim piece below the stool, against the wall
Casing Damage and Repair
Interior casing damage is common around windows: paint cracking at the miter joints (top corners), wood rot on exterior casing from failed caulk, and nail pops where the trim has shifted. Miter joint failures can be re-glued and filled. Rotted exterior casing sections can be replaced in-place without disturbing the window. Cost for professional casing replacement: $50–$150 per window depending on profile and paint.
