How to Install Baseboards

Using an I-beam or box beam level (preferably a 4-foot one), determine if the floor is level. If it’s not, find the lowest point in the room and nail a scrap piece of baseboard to the wall. Using the top of the scrap baseboard as a baseline, use a pencil to make horizontal marks around the room at the same level. Using a chalk reel, snap a chalk line around the room on the wall. This will mark where the top edge of the baseboard should be once installed.

Starting with the longest board and working your way around the room, measure baseboards one at a time, from longest edge to longest edge, and cut with a miter saw. If you don’t have a miter saw, use a miter box and back saw. Cut and fit as you go or cut and label each piece with the corresponding wall placement. When cutting baseboards for inside and corner joints, cut at a 45-degree angle. Add about 6 to 12 inches to the measurement for each wall to account for outside corners. 

If your baseboards are unfinished, use primer and paint them prior to installation.

If your floors aren’t level, you’ll need to scribe the baseboards so that they follow the contours of the floor and create an even finish. Start by setting your first piece of baseboard at an inside corner against the wall. Level the board, then tack it in place on the wall. Use a compass to determine the vertical distance between the chalk line and the board’s top corner. 

Next, hold the compass pencil against the baseboard with the point against the floor. Drag the compass the length of the board along the floor to draw a line across the bottom of the baseboard. Remove the baseboard, set the circular saw bevel at -5 degrees and cut at the scribe line with the face of the cut on the side toward the wall. Trim the board down to the pencil line. Refit the board to the wall to see if it’s level. If not, use sandpaper to bevel the board for an easier fit.

Attach the baseboards to the studs, using finishing nails and a brad nailer. If you don’t have a brad nailer, a hammer will do. Nails should go in at a slight downward angle, near the top and bottom of the board. 

When working with the outside corners, place the board against the wall and mark a vertical line on the back of the board to guide the cut. Repeat the process with the other corner board. Miter cut both boards at 45 degrees.

If you notice small gaps either between the wall and the baseboard or in the joints, use a caulk gun along with moulding and trim caulk to fill in the gaps. If needed, use a damp cloth to wipe away any excess caulk to give a clean finish where the baseboard meets the floor.