Trim Windows and Doors
Frame your windows and doors with beautifully installed casing. Learn techniques for dormer windows, skylights, and interior doors in your converted attic.
Why Quality Window and Door Trim Matters
Window and door casing transforms rough openings into elegant architectural features. Well-installed trim draws the eye, frames views, and elevates the entire room's appearance. In attic conversions with dormer windows and skylights, trim work is especially visible and impactful. Taking time to achieve consistent reveals, tight miters, and proper proportions makes your converted attic feel custom-built rather than hastily finished.
Common Trim Styles
Colonial
- Profile: Curved, ogee details
- Width: 2-1/4" to 3-1/2"
- Best for: Traditional homes
- Corners: Mitered
Craftsman
- Profile: Flat, simple lines
- Width: 3-1/2" to 5-1/2"
- Best for: Arts & Crafts style
- Corners: Butted with head cap
Modern
- Profile: Square, minimal
- Width: 2" to 3"
- Best for: Contemporary spaces
- Corners: Mitered or drywall returns
Tools & Materials Needed
Step-by-Step Installation Guide
Measure and Calculate Materials
Plan your trim work for efficient material use:
- •Measure the height and width of each window and door opening
- •Calculate linear feet needed: (2 x height) + width + 10% for each opening
- •Choose casing style that matches existing trim in your home
- •For windows with stools, add stool and apron material to your list
- •Mark the reveal (typically 3/16") on all jambs before starting
Install Window Stools and Aprons
For traditional window trim, start with the sill components:
- •Cut stool to extend 1" past where side casings will end on each side
- •Notch stool around window jambs if installing against the window
- •Level and nail stool to framing beneath window
- •Cut apron same length as distance between outer edges of side casings
- •Install apron centered under stool, tight against the wall
Alternative: For a cleaner modern look, skip the stool and apron and use picture-frame casing on all four sides.
Install Side Casings
Side casings go up next, setting the stage for the head casing:
- •Mark the reveal line on both side jambs (typically 3/16" to 1/4")
- •Measure from stool top to reveal mark at head jamb
- •For mitered corners, add the width of casing to your measurement
- •Cut 45-degree miter at top (for mitered style) or square cut (for butted style)
- •Nail into jamb near inner edge and into wall framing near outer edge
Install Head Casing
The head casing completes the frame:
- •For mitered corners: Measure between outer edges of side casings at miter points
- •For butted corners: Measure between outer edges plus 1/4" overhang each side
- •Cut miters or square cuts to match your style
- •Dry fit before nailing to ensure tight joints
- •Nail through head casing into side casings at corners for strongest joint
Tip: Apply wood glue to mitered corners before nailing. This creates a much stronger joint that won't open up over time.
Finish and Touch Up
Professional finishing makes trim look flawless:
- •Set all nail heads below surface with a nail set
- •Fill nail holes with wood putty or paintable wood filler
- •Sand filler smooth when dry
- •Caulk the gap between casing and wall (outer edge)
- •Prime bare wood and apply finish paint or touch up pre-finished trim
Pro Tips
- ✓Use a combination square to mark consistent reveals on all jambs before cutting any casing
- ✓For dormer windows, use a bevel gauge to capture ceiling angles where they meet the head casing
- ✓Cut test pieces from scrap to dial in tricky angles before cutting good material
- ✓For skylights, consider flexible PVC trim that can follow curves and unusual angles
Frequently Asked Questions
What is the standard reveal for window and door casing?▼
The standard reveal (the amount of jamb visible between the edge and the casing) is 3/16 to 1/4 inch. This creates a shadow line that defines the transition and allows room for adjustment. Mark the reveal on all jambs before installing casing for consistent results.
How do I trim a dormer window in an attic?▼
Dormer windows are trimmed similarly to standard windows, but you may need to account for angled ceiling transitions. Install a stool and apron at the bottom, side casings, and a head casing. Where the window meets the sloped ceiling, use a return or transition piece to connect the horizontal head casing to the angled ceiling line.
Should I use mitered or butted corners for window trim?▼
Both methods work well. Mitered corners (45-degree cuts) create a seamless, elegant look but require precise cuts. Butted or picture-frame joints (square cuts with head casing sitting on top of sides) are easier and more forgiving. Match the style used elsewhere in your home for consistency.
How do I trim around a skylight in an attic?▼
Skylights require drywall returns from the roof opening down to the ceiling plane. These splayed openings are then trimmed with casing along all four sides. The angles can be complex - use a bevel gauge to capture exact angles and cut test pieces from scrap. Consider using flexible trim for curved skylights.