Baseboards are the visual frame at the bottom of every wall — the trim that defines a finished room from a construction shell. Done well, they read as architectural detail; done poorly, they show every gap and miscut. The job depends on three skills: cutting consistent mitres at corners, scribing for uneven floors, and getting cope joints clean at inside corners.

This guide covers a typical room with rectangular geometry and finished flooring already in place. Tile floors, very old uneven walls, and curved walls add complexity covered in pro builds.

Before you start

Three things to settle:

1. Mitre vs cope joints. Outside corners (corners that point into the room): always 45-degree mitres. Inside corners (corners that point away from the room): coped joints — the second piece is cut to match the profile of the first piece, not mitred. Cope joints look better and tolerate wall movement; mitred inside corners open up over years.

2. Floor unevenness. Floors are rarely perfectly level. Baseboards installed straight will show varying gaps below them where the floor sags. The fix is scribing — marking and cutting the bottom of the baseboard to match the floor contour. For minor unevenness (under 1/8 inch), shoe moulding (small quarter-round) covers the gap. For major unevenness (over 1/4 inch), scribe.

3. Material choice. Pre-primed MDF: cheap, smooth, paint-grade. Suits modern simple profiles. Pine: stainable, accepts both stain and paint. Slightly more expensive but more durable. Solid hardwood (oak, maple): premium feel, stain-grade, expensive. Picture-frame quality finishes.

What you'll need

Tools

Mitre saw (compound mitre saw preferred for cope cuts)
Coping saw (for inside corner cope joints)
Tape measure
Pencil and combination square
Stud finder
Brad nailer (18 gauge) or finish nailer with compressor
Hammer and nail set (backup if no nailer)
Caulking gun
Sander or sanding block
Painter's tape

Materials

Baseboard material (calculate length plus 10% waste)
18-gauge brad nails (1.5 to 2 inches)
Wood filler
Painter's caulk (paintable acrylic latex)
Primer and paint (for raw or stain-grade material)
Construction adhesive (for masonry walls or for extra hold)

Cope inside corners; mitre outside

Inside corners (where two walls meet pointing inward, like a typical room corner): cope the second piece to match the first piece's profile. The first piece runs into the corner with a butt cut; the second piece is shaped to fit against the first piece's face.

Outside corners (the corners of a chimney bump-out, around a doorway): both pieces meet at 45-degree mitres. Mitred outside corners are clean and simple.

Mitring inside corners works in theory but in practice the joints open up as the house moves seasonally. Cope joints stay tight.

Step-by-step instructions

Measure the room and plan piece order

Sketch the room. Number each wall section in the order you'll install — typically starting with the longest wall opposite the door.

Plan piece lengths. Long single pieces look better than spliced; if a wall exceeds your stock length (typically 8 or 16 feet), splice with a 45-degree scarf joint at a stud location.

Find studs and mark them

Sweep each wall with a stud finder, marking stud locations with painter's tape just above where the baseboard will sit (you'll see the marks during install).

Studs are the nail targets. Drywall alone won't hold baseboard nails reliably.

Cut and install the first piece

Cut the first baseboard to length with both ends square (no mitre, no cope). Run it from the inside corner of one wall to the inside corner of the next.

Position against the wall, against the floor. Hold while nailing — drive 18-gauge brads through the baseboard into studs, every 16 inches.

Use the brad nailer set to a depth that drives the brad just below the baseboard surface (heads slightly recessed, ready for filling).

Cope the next piece (inside corner)

For the next piece going around an inside corner: cut a 45-degree mitre that exposes the baseboard's profile.

Use a coping saw to cut along the visible profile line on the mitred face. The result is a cut that matches the profile of the first piece.

Test fit. The coped end should sit cleanly against the face of the first piece. Adjust with the coping saw or sandpaper until tight.

Cut and install the next piece

Measure from the coped end to the next corner or wall. Cut the other end to length.

Position and nail in place. The coped end sits tight against the first piece; the far end butts the next corner.

Mitre outside corners

For outside corners (the corner of a chimney bump-out, doorway return), cut both pieces at 45 degrees on the mitre saw. The two angled cuts meet at the corner forming a clean 90-degree outside corner.

Test fit. If the corner doesn't close cleanly, the wall isn't truly square — adjust the mitre angle (e.g., 44 or 46 degrees) to compensate.

Scribe for floor unevenness if needed

If gaps appear between the baseboard bottom and the floor, scribe: with the baseboard held in place, run a pencil along the floor with the pencil tip touching the floor and the side resting against the baseboard. The line drawn on the baseboard matches the floor contour.

Cut along the scribe line with a jigsaw or careful coping-saw work. Re-install — the baseboard now matches the floor.

Continue around the room

Work systematically around each wall. Inside corners cope; outside corners mitre.

Keep nail spacing consistent — every 16 inches into studs, plus one nail near each end of each piece.

Fill nail holes and joints

Fill brad-nail holes with paintable wood filler. Sand smooth after dry.

Caulk along the top edge of the baseboard where it meets the wall — gaps between baseboard and wall are normal because of slight wall variations. Caulk hides these gaps for a clean line.

Prime and paint (or stain)

Pre-primed MDF needs only the topcoat. Raw pine needs primer first.

Apply two coats of trim-grade paint (semi-gloss or satin). Lighter sand between coats with 220-grit for the smoothest finish.

Stain-grade work uses stain plus topcoat (polyurethane). Different process from painting.

Common mistakes that cost you

Mitring inside corners. Joints open up as house moves. Cope inside corners; mitre outside.
Nailing only into drywall. Doesn't hold under stress. Always nail into studs every 16 inches.
Skipping caulk along the top. Gaps between baseboard and wall are visible without caulk. A bead of caulk hides imperfections.
Wrong material for the application. MDF in moisture-prone areas swells. Use solid wood or PVC trim in bathrooms and basements.
Rushing the cope joint. A bad cope joint shows forever. Take time to fit the cope tightly; sand if needed.

Frequently asked questions

How tall should baseboards be?

Standard heights: 3-4" for traditional homes, 4-6" for modern, 6-8" for formal or large rooms. Taller baseboards read as more architectural.

Match the existing baseboard height in the rest of your home unless you're updating the entire house. Mismatched heights between rooms looks unintentional.

Should I install before or after flooring?

After flooring is the modern standard — baseboards sit on top of the finished floor, with shoe moulding (quarter-round) covering any gap between baseboard bottom and floor.

Before flooring is older approach. Required only if flooring extends under baseboards (unusual).

Is shoe moulding necessary?

Shoe moulding is the small quarter-round trim along the bottom of baseboards. It hides gaps between baseboard and floor — useful when floors are uneven or when the wall isn't perfectly plumb.

Modern simple-profile baseboards often skip shoe moulding for a cleaner contemporary look — but require very level floors and careful baseboard fitting.

When to call us instead

Trim work is one of the trades where craftsmanship is most visible. Coped joints, mitred returns, and stain-grade finishes are skills that take years to perfect. For high-end homes or stain-grade installs, professional trim carpentry is often worth the cost.

Book a free 60-minute site visit →

Related Ottawa services

If you're updating trim and finishing as part of a larger renovation, our residential renovation team handles trim carpentry as part of fixed-price scopes. Book a free 60-minute consultation.