Interior PhaseStep 53 of 65

Trim and Millwork Installation

Install all interior trim and millwork throughout your home. Baseboards, door and window casing, crown molding, wainscoting, and custom built-in details transform basic rooms into finished, polished spaces with architectural character.

Quick Summary

Typical Cost

$5,000 - $25,000

Time Frame

5-10 days

Difficulty

Professional Recommended

Why Trim and Millwork Matters

Trim and millwork are often called the jewelry of a home, and for good reason. While walls, floors, and ceilings form the bones of a room, trim provides the finishing details that define architectural style and perceived quality. Well-executed millwork can make a basic home feel custom and expensive, while poor trim installation makes even high-end finishes look cheap.

In a whole-home remodel, millwork represents one of the final installation steps but should be planned from the beginning. Trim profiles, materials, and heights should complement your chosen design style whether that is traditional with elaborate crown and panel molding, transitional with clean simple profiles, or contemporary with minimal reveals and flat stock.

Quality trim installation requires skilled carpentry. Joints must be tight, corners precise, and transitions seamless. Unlike many other trades where minor imperfections are hidden, trim work is constantly visible and at eye level. The difference between amateur and professional installation is immediately apparent to anyone who looks closely.

Step-by-Step Guide

Finalize Trim Style and Selections

Choose trim profiles that match your home's architectural style and interior design. Decisions include baseboard height and profile, door and window casing style, crown molding complexity, and any decorative treatments like wainscoting or chair rail.

Select baseboard height: 5-7 inches for standard ceilings
Choose casing profile: traditional ornate or modern flat stock
Determine crown molding scope: all rooms or select spaces
Plan decorative treatments: wainscoting, panel molding, coffered ceilings
Match existing trim if partial remodel or choose cohesive new style

Order Materials and Allow Acclimation

Calculate linear footage for all trim types with 15-20% overage for cuts and waste. Order materials 2-4 weeks before installation. Wood trim must acclimate to home humidity and temperature conditions for at least 48-72 hours to prevent expansion or shrinkage after installation.

Measure all linear footage by room and trim type
Add 15-20% overage for cuts, waste, and future repairs
Order matching corner blocks, rosettes, and plinth blocks
Acclimate wood trim 48-72 hours in installation environment
Store flat and straight to prevent warping

Install Door Casing

Begin with door casing as it establishes reveal dimensions and style for the home. Install casing around all interior door frames maintaining consistent reveals (typically 3/16-inch from jamb edge). Use mitered corners for traditional looks or butted corners with rosette blocks for Victorian style.

Establish consistent reveal from door jamb (3/16-inch typical)
Cut precise 45-degree miters for corner joints
Nail casing to jamb and framing with finish nailer
Check for plumb and square as you go
Install both sides and head casing before moving to next door

Install Window Casing and Sills

Window trim typically includes stool (interior sill), apron (trim below stool), and casing on sides and head. Picture frame style uses casing on all four sides without a stool. Match window casing profile to door casing for consistency.

Install stool first with proper horns extending past casing
Add apron beneath stool matching casing profile
Install side casing resting on stool
Complete with head casing at top
Ensure tight fit against window frame and wall

Install Baseboards Throughout

Baseboards are the most visible trim in any home. Install after flooring is complete. Cope inside corners for tight joints that stay tight as the house moves. Miter outside corners. Use long pieces to minimize joints on long walls.

Start with longest walls using full-length pieces
Cope inside corners for professional results
Miter outside corners at 45 degrees
Scarf joints at 45 degrees on long runs
Nail to studs and bottom plate for secure attachment

Install Crown Molding

Crown molding requires the most skill due to compound angles and overhead work. Install blocking where ceiling framing does not align with walls. Cut compound miters for outside corners and cope inside corners for best results.

Install blocking or nailers at ceiling line if needed
Mark spring angle reference lines on wall and ceiling
Cut compound miters holding crown at proper angle
Cope inside corners for tight, lasting joints
Use two-person team for long pieces

Install Wainscoting and Wall Treatments

Decorative wall treatments like wainscoting, board and batten, panel molding, and picture rail add significant architectural interest. Plan layout carefully to ensure balanced panel sizes and consistent rail heights throughout connected spaces.

Establish consistent height for chair rail or wainscot cap
Lay out panel molding for balanced proportions
Install horizontal rails first then vertical stiles
Use construction adhesive plus nails for secure panels
Plan outlets and switches within panel layout

Complete Built-In Details

Custom built-ins like bookcases, window seats, entertainment centers, and architectural niches require careful trim work to look integrated rather than added. Wrap openings with matching casing and add crown or cap molding to top of built-ins.

Match built-in trim to room millwork profiles
Add face frames to conceal cabinet box edges
Install crown or cap molding on top of built-ins
Trim out niches and pass-throughs with matching casing
Integrate lighting valances and cord management

Fill, Caulk, and Sand All Trim

This finishing step separates professional work from amateur installations. Fill all nail holes with appropriate filler, caulk gaps between trim and walls, and sand smooth. Quality prep work is essential for a flawless painted finish.

Set all nail heads below surface with nail set
Fill holes with wood filler (stain grade) or spackle (paint grade)
Caulk gaps where trim meets wall with paintable caulk
Sand filled areas smooth when dry
Inspect entire installation for missed spots

Prime and Paint All Trim

Apply primer if not pre-primed, then apply two finish coats for durability. Trim paint should be semi-gloss or satin for cleanability and subtle sheen contrast with walls. Use quality paint and brushes for smooth, professional results.

Apply primer to bare wood and filled areas
Lightly sand between coats for adhesion
Apply first finish coat with quality brush or spray
Apply final coat after first coat cures
Remove painter's tape before paint fully cures

Trim Materials Comparison

Paint-Grade MDF

Medium-density fiberboard with smooth paintable surface.

Cost: $1-3 per linear foot
Pros: Smooth finish, no grain, stable
Cons: Heavy, swells with moisture
Best For: Paint-grade interior trim
Avoid In: Bathrooms, high humidity areas

Finger-Joint Pine

Short wood pieces joined together, designed for painting.

Cost: $2-4 per linear foot
Pros: Real wood, lighter than MDF, stable
Cons: Joints may telegraph through paint
Best For: Paint-grade applications
Avoid: Cannot be stained

Clear Pine or Poplar

Solid wood suitable for paint or light stain.

Cost: $3-6 per linear foot
Pros: Stainable, workable, traditional
Cons: Soft wood dents easily
Best For: Paint or light stain finishes
Note: Poplar takes paint better than stain

Oak or Hardwood

Premium solid wood for stained or natural finishes.

Cost: $6-15 per linear foot
Pros: Beautiful grain, durable, premium look
Cons: Expensive, harder to work
Best For: Stained trim, traditional homes
Options: Oak, maple, cherry, walnut

Cost Breakdown (2,500 sq ft Home)

Trim Type	Linear Feet	Material Cost	Installed Cost
Baseboards (5.25")	500 LF	$750-1,500	$2,000-4,000
Door Casing (15 doors)	240 LF	$360-720	$1,200-2,400
Window Casing (12 windows)	200 LF	$300-600	$1,000-2,000
Crown Molding (3 rooms)	150 LF	$450-900	$1,500-3,000
Chair Rail/Panel Molding	100 LF	$200-400	$800-1,600
Closet Shelving/Trim	Varies	$300-600	$800-1,500
Painting Labor	-	$500-800 (paint)	$1,500-3,000
Total	~1,200 LF	$2,860-5,520	$8,800-17,500

Pro Tips

Learn to Cope Inside Corners

Coped inside corners stay tight as the house settles while mitered corners open up. Cut a 45-degree miter, then use a coping saw to cut along the profile. It takes practice but produces vastly superior results.

Pre-Prime Before Installation

Prime and apply first coat to trim before installing. This saves time, provides better coverage on all sides, and makes finish painting faster. Only back faces can be skipped on interior paint-grade trim.

Use Scarf Joints on Long Runs

When joining trim on long walls, cut 45-degree scarf joints rather than butt joints. The angled joint is less visible and stays tighter. Always locate joints over studs and glue the joint for seamless results.

Invest in Quality Saw Blades

A sharp, high-tooth-count blade makes the difference between clean cuts and torn edges. Use 80-100 tooth blades for finish trim work. Replace or sharpen blades regularly - dull blades ruin trim.

Check Walls Before Installing

Hold trim against walls to check for bows and bumps before nailing. Scribe trim to walls where needed. Never force trim against crooked walls - it will spring back and open joints.

Caulk Before Final Paint

Caulking fills gaps but shows brush marks if painted over wet. Apply caulk, smooth with wet finger, let dry 24 hours, then apply final paint coat. This creates seamless transitions between trim and walls.

Common Mistakes to Avoid

Mitering Inside Corners

Inside corner miters look good initially but open as the house settles and wood moves with humidity changes. Coped joints overlap and stay tight regardless of movement. Take time to learn coping for professional results.

Skipping Acclimation

Installing trim straight from a cold warehouse or delivery truck causes it to expand or contract after installation. Wood needs 48-72 hours to reach equilibrium with room conditions. Gaps and buckles result from skipping this step.

Inconsistent Reveals

The reveal (gap between door jamb and casing) must be consistent throughout the home. Use a reveal gauge or combination square set to 3/16-inch. Inconsistent reveals look amateur and cannot be fixed without reinstallation.

Using MDF in Wet Areas

MDF swells when exposed to moisture and never recovers. Do not use standard MDF in bathrooms, near exterior doors, or in laundry rooms. Use moisture-resistant MDF or solid wood in these locations.

Poor Nail Placement

Nails too close to edges split trim. Nails missing studs provide no holding power. For baseboards, place nails 1/2-inch from edges into studs. For casing, nail into both jamb and framing. Use stud finder and mark locations before nailing.

Frequently Asked Questions

What is the standard baseboard height for modern homes?

Modern homes typically use 5.25 to 7.25-inch baseboards for standard 8-9 foot ceilings. Taller ceilings (10+ feet) look best with 8-inch or taller baseboards. Minimalist modern designs may use 3-4 inch flat profiles. The general rule is taller ceilings warrant taller baseboards for proper visual proportion.

Should trim be painted before or after installation?

Pre-priming trim before installation saves significant time and provides better coverage. Apply primer and first coat before installing, then fill nail holes, caulk, and apply final coat after installation. This method results in a superior finish while reducing labor time. Stained trim should always be finished before installation.

What is the difference between MDF and wood trim?

MDF (medium-density fiberboard) trim is more affordable ($1-3 per linear foot), takes paint beautifully, and resists warping. However, it cannot be stained, swells when wet, and is heavier. Wood trim costs more ($3-15 per linear foot) but can be stained, handles moisture better, and has superior durability. Use wood in moisture-prone areas.

How do I cut perfect crown molding corners?

Crown molding corners require compound miter cuts because the molding sits at an angle. Inside corners are best coped - cut a 45-degree miter then use a coping saw to cut along the profile. Outside corners use compound miter cuts. For 90-degree corners with standard 38-degree spring angle crown, set miter to 31.62 degrees and bevel to 33.86 degrees.

What size finish nails should I use for trim?

Use 15 or 16 gauge finish nails for baseboards, crown molding, and larger trim pieces - these have the holding power for heavier materials. Use 18 gauge brad nails for smaller trim, thin casing, and delicate work. Nail length should be at least 1.5 times the trim thickness. For drywall applications, ensure nails reach studs or use construction adhesive.