How To Install Baseboards In 10 Steps

Baseboards were often three-piece affairs consisting of a flat plank, a decorative cap molding, and a rounded shoe molding to cover gaps along the floor. “In old houses, you often see the fanciest baseboard in the front room downstairs,” says This Old House general contractor Tom Silva. In houses built after World War II, however, fancy gave way to cheap, and the vital floor-to-wall transition became the domain of thin, featureless one-piece trim. Fortunately, it’s easy to replace modern moldings with taller, thicker, two- or three-part baseboards. Running baseboard is also good for perfecting carpentry skills. The joints required are simple butts, miters, and copes, and the same basic installation steps apply to all trimwork.

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When starting from scratch, Tom Silva prefers the look of a base that’s at least 6 inches high and ½ to ¾ inches thick, topped with a separate, deeply profiled cap molding. But if he’s remodeling a house graced with good-looking baseboards, he tries his best to match the new trim to what’s already there. Making a new baseboard the same height as the original isn’t difficult; finding a cap molding with the same profile can be, especially on an old house. Sometimes Tom will get lucky and locate the profile he needs from the 100 or so that good millwork shops keep in stock. Sometimes he’ll combine two or more of those moldings to create a shape that is close. But when an exact replica is needed, he’ll have custom molding milled up.

Planning Ahead

To determine the amount of baseboard material you need, measure each straight section of the wall and round up to the nearest whole-foot dimension divisible by two. A week before installation, bring the wood inside to acclimate. Start running baseboard against inside corners and work toward outside corners.

Steps on How to Install Baseboard

1. Prep Work: Measure, Number and Mark

Measure and cut the baseboards for each wall. Boards that meet outside corners should be a few inches longer than the wall to allow for miter cuts. Number the back of each board and write that same number on the wall where the board will go. Find and mark the studs in the wall; they’ll serve as the firm base for nailing the baseboard.

Tip: Studs are usually placed 16 inches on-center, so after locating the first one you may be able to locate others using a tape measure. On older homes, verify locations with a nail.

2. Establish the Baseboard Height

Set a 4-foot level on the floor next to the wall to see if the floor is level. If not, move the level across the floor to find its lowest point. At that point, tack a scrap piece of baseboard to the wall with a nail. Using the top of this baseboard piece as a benchmark, make horizontal marks every few feet at the same level on the walls around the room. Snap a chalk line between the marks around the perimeter of the room to show where the top edge of all the baseboards should land when they’re installed. Starting at an inside corner, hold the first board against the wall, level it, then tack it in place with a nail or two. Set your compass points to span the vertical distance between the chalk line and either of the board’s top corners.

3. Scribe for a Tight Fit

Without changing the spread of the compass’s legs, hold the pencil on the baseboard and the point against the floor. Slide the compass along the floor over the board’s length, keeping the points aligned vertically. With a circular saw set for a 2- to 5-degree bevel, cut alongside the scribe line so the face of the cut will be on the side toward the wall. Trim the beveled edge down to the line with a block plane. When the scribed baseboard is put back on the wall, its top edge should line up with the chalk line snapped in Step 2.

Tip: Beveling the board’s bottom edge makes it much easier to scribe-fit.

4. Nail Baseboard to Wall

Set the scribed baseboard in place. Next, at each stud location, hammer two 8d finish nails through the board, at a slight downward angle, near its top and bottom edges. To avoid marking the wood, use a nail set to drive the heads just below the wood surface.

5. Mark Outside Corner Joints

Fit one end of the board snugly against the inside corner (or casing), and at the other end draw a vertical line up the back of the board, using the edge of the outside corner to guide the pencil. Mark the top of the board to show the direction of the miter. Remove the marked board and place the one that will make up the miter’s other half against the adjacent wall. Mark the same way.

6. Miter-Cut Outside Corner Joints

Set a compound miter saw to 45 degrees and cut each miter just outside of the line. This way, the joint can be fine-tuned. Place both boards back against the wall and examine the joint. If it isn’t tight on the side and top, go back to the saw or pick up a block plane and trim the wood until it is.

Tip: “You want to cut next to the line marking the joint,” says Tom. “Then there’s room to fine-tune and get it tight.”

7. Cut Biscuit Slots

To make sure an outside miter joint stays tight, connect the two halves with glue and Number 10 compressed-wood biscuits. First, hold the two boards tightly against the outside corner and pencil a mark in two places across the joint. The marks should be equidistant from each other and from the edges of the board. Then remove the boards, set the biscuit joiner perpendicular to the cut face, and adjust the depth of its fence so the cut will be nearer to the back side of the boards. Align the tool’s centerline with a mark and plunge-cut a slot into the face of the cut. Do the same thing at the next mark.

8. Assemble the Biscuit Joints

Squeeze carpenter’s glue into both slots and over the face of each half of the miter cut. Then slip a biscuit into each slot on one board and bring the two boards together. Place the boards back on the wall and drive two 8d finish nails into the wall on each side of the miter. Between these nails, drive a 4d finish nail through the joint and into the end grain of the opposite piece. Tap nail heads below the wood surface with a nail set. Where two boards meet on a straight run, make a scarf joint by mitering the ends in opposite directions at a point where there’s a stud. Glue and overlap the miters, then nail through the piece that covers the joint (not through the joint itself) and into the stud. For inside corners, simply butt the baseboard ends together, then nail them to the wall.

9. Nail on the Cap Molding

When using a cap molding, place it on the base to see if the back of the molding fits snugly against the wall. Secure it at each stud with an 8d nail driven at a slight downward angle through the thicker parts of the molding. If there are gaps behind the molding and no stud to nail into, squeeze a bead of construction adhesive on the back of the molding at those spots and nail the molding to the studs, as above. Then nail the molding to the wall between the studs to hold it in place until the adhesive sets.

10. Sand the Cap Molding

To create tight fitting joints where cap molding meets at inside corners, cope the joints. Join outside corners with miters, marking and cutting as in Step 4. Glue miter joints together; adding biscuits or nails may cause the narrow molding to split. Where two caps meet on a long wall, make a scarf joint as described in Step 8. Sand all the mitered corners lightly with fine sandpaper to remove any sharp edges. The baseboard trim is now ready to be primed and painted.