Window Casing

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.