Interior Trim Guide: Baseboard, Casing & Moulding for LA Remodels

Trim is the last thing installed and the first thing anyone notices. It is also where a remodel either reads as finished or reads as almost finished, and the difference usually comes down to three decisions made before a single piece is cut: what the trim is made of, how tall the baseboard is, and whether the casing and base are talking to each other. This guide covers the profiles and materials we stock, how to size them for a typical Los Angeles house, and the fastening and finishing details that decide whether the joints stay closed.

Material first: MDF, primed pine, or composite

Almost all painted interior trim now comes down to MDF or finger-jointed primed pine, and the choice is about where the trim is going rather than about quality. MDF is dimensionally stable, mills to a very crisp profile and takes paint beautifully, which makes it the default for painted base and casing in dry interior rooms. Primed pine holds a fastener better, tolerates a knock, and handles the occasional damp better than MDF does — worth choosing where a run will get kicked or where humidity is a factor.

Composite and PVC are the third category and they exist for wet and exterior-adjacent work. A PVC composite casing will not swell or rot at a bathroom door or a garage opening, and the composite sill moulding and composite trim moulding are made for exterior window and door detailing where wood would eventually fail.

One caveat the table cannot carry: MDF and pine both take paint well, but they do not take it identically. Pine grain and finger joints can telegraph through a thin coat, and MDF drinks primer at cut ends. If a run mixes both materials, prime the whole thing before topcoat rather than assuming the factory prime is enough.

Sizing baseboard for a Los Angeles house

Baseboard height should follow ceiling height and the age of the house, not fashion. A post-war LA bungalow or a tract house with eight-foot ceilings sits comfortably with base in the two-and-a-half to three-and-a-half inch range: the 7/16 in. x 2-1/2 in. MDF base and the 1/2 in. x 3-1/2 in. MDF base are the everyday sizes for that house.

Nine and ten-foot ceilings, and the taller volumes in newer ADUs and additions, need more base or the room looks unfinished at the floor. The 4-1/2 in., 5-1/2 in. and 7-1/4 in. profiles cover that range. Craftsman-style flat profiles like the 3-1/2 in. Craftsman base suit the bungalow stock that fills much of Highland Park, Pasadena and the older Westside.

Buy in the longest length the room and the access allow. A sixteen-foot stick that runs a wall in one piece has no joint in it, and a joint in the middle of a long wall is the one that opens up first. Where a room genuinely cannot take a long stick — a stairwell, a tight hallway, a second-floor unit with no straight path — the eight and twelve-foot lengths exist for exactly that reason. The full range is in our moulding collection and the primed boards collection.

Casing: matching the door and window openings

Casing hides the gap between the jamb and the drywall, and its width sets the visual weight of every opening in the house. Two-and-a-quarter inch casing such as the 9/16 in. x 2-1/4 in. Craftsman casing is the standard residential width and reads correctly next to a three-inch base. Three-and-a-quarter inch casing like the 11/16 in. x 3-1/4 in. profile goes with the taller bases above.

The relationship that matters is casing thickness against base thickness. Casing should be at least as thick as the baseboard it meets, so the base dies cleanly into the side of the casing instead of standing proud of it. Get that backwards and every door in the house has an awkward step where the two pieces meet — it is the single most common trim mistake in a DIY remodel, and it cannot be fixed with caulk.

For repetitive work, buy the way the job runs. Pro packs and mitered sets like the Craftsman casing set, the mitered pine casing 5-pack and the 20-pack of 7 ft. MDF casing cut and stage better than loose sticks when a house has fifteen identical doors. The whole range is in the casing collection.

Build-ups, bullnose and the pieces that are not base or casing

Crown and other tall treatments are usually not a single stock profile — they are a build-up. Flat S4S stock, surfaced on four sides, is the backbone of that: the 5-1/2 in., 7-1/4 in., 9-1/4 in. and 11-1/4 in. boards do the work in header casings, wainscot rails, box beams and layered cornice details. Stacking a flat board with a smaller profile gives you a heavier, more custom result than any single stick.

Bullnose profiles suit the rounded-corner drywall common in Southern California stucco-era and Spanish-revival houses, where a square-edged trim next to a bullnose corner never quite looks right. Stop moulding handles doors and windows, and stucco moulding is the transition piece where interior finish carry-overs meet exterior wall assemblies.

Fastening and finishing

Trim is nailed with finish or brad nails, and gauge is the decision. Fifteen and sixteen-gauge finish nails have the holding power for base, casing and anything carrying its own weight; eighteen-gauge brads leave a smaller hole and suit small profiles, returns and glue-ups where the nail is really just a clamp. We stock the range in the finishing nails collection, including 2-1/2 in. 15-gauge and 1-1/2 in. 16-gauge finish nails.

Length is set by what the nail has to reach. Trim nails need to pass through the moulding, through the drywall, and land properly in framing or blocking — a nail that stops in drywall is holding nothing, and that is why base pulls away from the wall between studs. Where trim is going onto drywall over steel studs, trim-head screws such as the #6 x 1-5/8 in. trim-head wood screw hold where a nail will not; our note on choosing the right screws for carpentry covers the rest.

Finishing is where the joints disappear. Fill nail holes, caulk the top edge of the base and the outside of the casing where they meet the wall, and leave the mitres to glue rather than caulk — a caulked mitre reopens, a glued one does not. Choose the sealant deliberately; our sealant comparison explains why paintable acrylic latex belongs on interior trim and silicone does not. Prime any bare cut ends before topcoat — our guide to oil-based versus water-based primer covers which to reach for.

Ordering trim for an LA remodel

Measure by room and by wall, add ten to fifteen percent for mitres, cuts and the piece that splits, and order all of one profile in one go. Profiles are manufactured in runs, and matching a partial reorder to an existing installation is far harder than buying the extra stick up front.

Think about how it gets into the building. Sixteen-foot MDF is heavy, flexible and easy to crease, and a hillside house with a narrow stair is a real constraint on stock length — that is a delivery conversation, not an afterthought. Store trim flat and indoors before install: MDF left leaning against a wall in a hot garage for a week will not be straight when you come back to it.

We deliver moulding, casing and finish fasteners across Los Angeles County. Send the room dimensions and the ceiling height and we will put the profile list together.

Frequently asked questions

What height baseboard should I use?

Scale it to the ceiling. Eight-foot ceilings generally suit base in the 2-1/2 to 3-1/2 in. range; nine and ten-foot ceilings carry 4-1/2 to 7-1/4 in. comfortably. Matching the existing base in the rest of the house usually matters more than any rule.

Is MDF trim better than pine?

For painted interior trim in a dry room, MDF gives a crisper profile and a smoother painted finish. Pine holds fasteners better and tolerates moisture and impact better. Neither is universally better — pick per location.

Can I use MDF trim in a bathroom?

Not where it can get wet. MDF swells irreversibly once water gets into the fibre, so use PVC composite or a moisture-tolerant material at showers, tubs and anywhere the floor gets mopped hard.

Should casing be thicker than baseboard?

At least as thick, yes. The baseboard dies into the side of the casing, so casing that is thinner than the base produces a visible step at every door. Check the two thicknesses against each other before ordering either.

What nail gauge is right for baseboard?

15 or 16-gauge finish nails for baseboard and casing, long enough to reach framing through the drywall. 18-gauge brads are for small profiles, returns and holding glued parts while they set, not for holding base to a wall.

Should I paint trim before or after installing it?

Prime and put the first coat on before install where you can — it is far faster on sawhorses than on your knees. Install, fill, caulk, then topcoat in place. That sequence gives the cleanest line at the wall.