Window Trim & Casing: Styles, Materials & Installation Guide

What Is Window Trim?

Window trim (also called window casing or window molding) is the decorative frame installed around the interior and/or exterior of a window opening. Trim serves two purposes: it covers the gap between the window frame and the surrounding wall, and it provides a finished, polished look that defines the window as an architectural element. Along with baseboards and crown molding, window trim is one of the three most impactful interior trim elements in any room.

The terms "trim," "casing," and "molding" are often used interchangeably, but technically: casing refers specifically to the frame around a door or window opening, trim is a broader term for any decorative millwork, and molding describes a piece of wood (or other material) that has been shaped into a specific profile.

Window Trim Styles

Colonial / Traditional

Colonial-style window trim features a profiled casing with curves, ogees, and decorative edges. The most common colonial profile is a 2-1/4 or 3-1/2 inch casing with a curved outer edge and a flat inner edge that meets the window frame. Corners are mitered at 45 degrees for a clean, formal look. Colonial trim pairs naturally with raised-panel doors and crown molding in traditional homes.

Craftsman / Arts & Crafts

Craftsman window trim uses flat, square-edged boards (typically 1x4 or 1x6 stock) with a distinctive header piece across the top that extends beyond the side casings. The header (also called a lintel trim or head casing) is usually thicker and wider than the side casings, creating a shelf-like projection. Corners are butted (not mitered), emphasizing the honest, straightforward construction philosophy of the Arts & Crafts movement.

Classic Craftsman proportions: 1x4 side casings (3.5 inches wide), 1x6 head casing (5.5 inches wide) projecting 1 inch past side casings on each side, optional 1x2 backband around the outer edge, and a flat stool (interior window sill) extending 1–2 inches past the side casings.

Farmhouse

Farmhouse window trim is typically flat stock similar to Craftsman but with wider proportions and simpler details. Wide 1x6 or 1x8 casings create a bold, substantial frame. The look is casual and unpretentious. Often paired with shiplap or board-and-batten wall treatments. Painted white is the classic farmhouse choice, though natural wood tones work well in modern farmhouse designs.

Modern / Contemporary

Modern window trim is minimal — thin, flat, and unadorned. Many modern homes use narrow 1x2 or 1x3 flat casings with sharp, clean edges. Some contemporary designs skip visible trim entirely, using drywall returns (where the drywall wraps into the window opening) for a completely frameless look. When trim is used, it's flush or nearly flush with the wall surface.

Victorian

Victorian window trim is the most ornate style, featuring multiple layered molding profiles, decorative rosette blocks at the corners (instead of mitered joints), fluted casings, and elaborate header treatments. Reproducing authentic Victorian trim typically requires combining several standard molding profiles or commissioning custom millwork.

Window Trim Materials

Solid Wood

Pine (White or Sugar Pine): The most common and affordable trim wood. Takes paint beautifully. Soft and easy to work with. Finger-jointed pine (short pieces joined end-to-end) is the most economical option; clear pine costs more but has no visible joints.

Poplar: Slightly harder than pine with a very smooth, uniform grain. Excellent for painted trim. Doesn't have the knots and resin pockets common in pine. The preferred choice of many professional trim carpenters for painted applications.

Oak: Strong, durable, and features prominent grain that looks beautiful with clear finish or stain. The classic choice for stained interior trim in traditional homes. Red oak is more common and affordable; white oak has a slightly more refined grain pattern.

MDF (Medium-Density Fiberboard): Not solid wood, but the smoothest possible surface for painted trim. No grain, no knots, no expansion and contraction. Available in pre-primed profiles ready to paint. More affordable than solid wood. Cannot be used in wet areas or exterior applications.

PVC / Cellular PVC

Cellular PVC trim looks like painted wood but is completely impervious to moisture, rot, and insects. It never needs painting (though it can be painted), won't split or crack, and lasts essentially forever. PVC trim is the standard choice for exterior window trim in new construction and is increasingly used for interior applications in bathrooms, kitchens, and high-humidity areas.

Cost: 30–50% more than pine for materials, but zero maintenance over its lifetime. Available in all standard profiles and can be worked with standard woodworking tools.

How to Install Interior Window Trim

Tools and Materials

Miter saw (for angled cuts), nail gun with 15-gauge or 18-gauge finish nails, measuring tape, combination square, wood filler, caulk, sandpaper, paint or stain, and the trim material itself.

Step-by-Step Installation

Step 1 — Mark your reveal. Set a combination square to 3/16 or 1/4 inch and use it to mark a consistent reveal (the small exposed edge of the window jamb visible between the jamb edge and the inner edge of the casing) on all four sides of the window jamb. This reveal creates a shadow line that makes the trim look professional and hides minor imperfections in the jamb-to-casing joint.

Step 2 — Measure and cut side casings. Measure from the reveal mark at the bottom (or stool) to the reveal mark at the top of the window. For mitered corners, add the width of the casing to this measurement and cut a 45-degree miter at the top. For butted (Craftsman) corners, cut the side casing square at the top.

Step 3 — Install side casings. Apply a thin bead of wood glue to the back edge. Align the inner edge with your reveal marks. Nail into the window jamb with thin nails near the inner edge, and into the wall framing (studs or jack studs) with longer nails near the outer edge. Nail every 12–16 inches.

Step 4 — Measure and cut the head casing. For mitered corners, measure between the outer edges of the side casings at the reveal line and add two casing widths (for the two miters). Cut 45-degree miters on both ends. For Craftsman style, cut the head casing to extend past the side casings by your desired overhang (typically 1 inch on each side).

Step 5 — Install head casing. Apply glue to mitered joints. Nail the head casing to the header framing and into the jamb. For mitered corners, drive a couple of cross-nails through the miter joint from above to hold it tight. Apply a dab of glue to the miter faces.

Step 6 — Fill and finish. Set all nail heads below the surface with a nail set. Fill nail holes and any gaps with wood filler. Caulk the joint between the outer edge of the trim and the wall (this hides any wall irregularities). Sand filler smooth when dry, prime, and paint or stain.

Cost Guide

1. Materials per window: Pine trim: $10–$
2. 3
3. Poplar: $15–$
4. 4
5. Oak: $20–$
6. 6
7. MDF: $8–$
8. 2
9. PVC: $15–$
10. 4
11. Add $3–$5 per window for nails, glue, caulk, and filler.

Professional installation: $65–$150 per window for basic casing. $100–$250 per window for elaborate Craftsman or Victorian styles with stool, apron, and multiple molding layers.

DIY savings: Trimming a window yourself saves $50–$150 in labor per window. A whole-house project (15–20 windows) saves $1,000–$3,000+ versus hiring a trim carpenter.