Install Baseboards and Trim
Baseboards and trim are the finishing touches that make your addition look complete and intentional. Matching existing profiles creates seamless flow between old and new spaces—or you may need to update trim throughout connected rooms for consistency.
Quick Summary
Time needed
1-3 days
Cost
$2-$8/linear ft installed
Professional help
Finish carpenter
Why This Step Matters
Trim work separates a "good enough" renovation from a quality one. Tight miters, consistent reveals, and matched profiles signal attention to detail. Poor trim work is immediately visible and hard to fix after painting.
Common Mistake
Using a different trim profile in the addition than existing rooms. Even if the addition has a door separating it, visible sight lines make mismatched trim obvious. Always match or commit to replacing trim in connected spaces.
Trim Types in a Home Addition
Baseboards
Cover the gap between flooring and walls. Standard heights are 3-1/4" to 5-1/4" for traditional homes, up to 7-1/4" for more formal spaces. Profile styles include colonial, craftsman, modern flat, and ranch.
Door Casing
Frames around door openings. Width typically 2-1/4" to 3-1/2". Should match baseboard style era. Mitered corners are modern; rosette blocks are traditional.
Window Casing
Frames around windows. Often matches door casing but may include a wider stool (interior sill) and apron beneath. Picture frame style (mitered all around) or traditional with stool/apron.
Crown Molding
Decorative transition between walls and ceiling. Optional but adds significant visual appeal. Typically 3-1/2" to 5-1/4" for residential. Complex to install—requires compound angle cuts.
Chair Rail / Wainscoting
Horizontal trim at chair-back height (30-36"). Often used in dining rooms and formal spaces. Only add if existing home has it—don't introduce new design elements that clash with home's style.
Matching Your Existing Trim
Remove a Sample Piece
Carefully remove a short section of existing baseboard from a closet or inconspicuous area. Cut it cleanly to show the profile. Take this sample to lumberyards and millwork shops for matching.
Check Standard Profiles
Many trim profiles are industry standards available at big box stores. Colonial, ranch, craftsman, and modern flat profiles are readily available. Measure height and compare profile curves to samples.
Pro tip: Take photos of your sample next to a ruler. Many lumberyards can identify profiles from good photos if you can't bring the sample.
Consider Custom Milling
If your trim is discontinued or unique, millwork shops can create custom knives to reproduce the profile. Cost is typically $150-$300 for the knife plus $3-$6 per linear foot for the trim.
Decide: Match or Replace All
If matching is difficult or expensive, consider replacing all trim in connected rooms. This is often faster and cheaper than perfect matching, and ensures consistent appearance throughout.
When to replace all: If your home has mismatched or damaged existing trim, an addition is the perfect opportunity to upgrade everything to a consistent, quality profile.
Trim Material Options
| Material | Cost | Best For |
|---|---|---|
| Finger-jointed pine | $0.70-$1.50/LF | Budget, painted finish |
| Solid pine/poplar | $1.00-$2.50/LF | Painted, smooth finish |
| MDF (primed) | $0.60-$1.20/LF | Painted, modern flat profiles |
| Oak/hardwood | $2.50-$5.00/LF | Stained, matching wood floors |
| PVC/cellular PVC | $1.50-$3.00/LF | Moisture areas, rot resistance |
Note: Costs are for materials only. Installation adds $2-$5 per linear foot depending on complexity and labor rates.
When to Replace Trim in Connected Rooms
Sometimes matching isn't practical, and replacing trim in adjacent rooms is the better solution. Consider this approach when:
Replace All When:
- • Existing profile is discontinued
- • Custom milling cost exceeds replacement
- • Existing trim is damaged or low quality
- • Open floor plan creates long sight lines
- • You're already repainting connected rooms
Match Only When:
- • Profile is readily available
- • Doorway separates addition from house
- • Historic home requires period accuracy
- • Budget is very tight
- • Existing trim is high quality/stained
The transition point: If you can't match exactly, make the transition at a doorway threshold rather than mid-wall. The door frame provides a natural break point that makes the change less noticeable.
Installation Best Practices
Acclimate Materials
Store trim in the conditioned space for 48-72 hours before installation. Wood expands and contracts with humidity—acclimation prevents gaps appearing after installation.
Cope Interior Corners
Professional carpenters cope interior corners rather than miter them. Coping creates tighter joints that don't open up as the house settles. Miters are fine for exterior corners.
Use a Finish Nailer
15 or 16 gauge finish nailers for baseboards; 18 gauge brad nailers for smaller trim. Set nail heads slightly below surface for filling. Nail into studs for baseboards, not just drywall.
Fill and Caulk Before Paint
Fill nail holes with wood filler. Caulk gaps between trim and walls with paintable latex caulk. These steps make the difference between amateur and professional results.
Frequently Asked Questions
Should I install baseboards before or after painting walls?
Install baseboards before final wall paint for the cleanest result. This allows caulking the top edge of baseboards, then painting walls down to meet the trim. Pre-primed trim can be final-painted after installation.
How do I handle out-of-square walls?
Most walls aren't perfectly square. Coping interior corners compensates for this. For mitered corners, cut slightly long and use a belt sander to adjust the angle. Caulk hides small gaps.
Is shoe molding necessary?
Shoe molding (quarter round) covers gaps between baseboards and flooring, especially important with floating floors that need expansion space. It's standard with hardwood but optional with carpet. Match your existing home's approach.
Can I reuse the trim I removed during demolition?
Sometimes. Carefully removed trim can be reinstalled if it's in good condition. However, removal often damages trim (splits, broken profiles). Budget for new trim and consider reuse a bonus.
Ready for the Next Step?
With baseboards and trim installed, your addition is ready for paint. The trim should be caulked and filled, creating smooth surfaces that will look professional once painted.