How to Install Crown Molding

Modern crown molding can be traced to the late Renaissance, when designers adapted elements of Greek and Roman architecture to ornamental plaster and wood cornices used to disguise and beautify the juncture of ceiling and wall.

The cornice’s curves, referred to by classical names such as scotia, cyma, and ovolo, add sculptural definition and visual interest to an otherwise characterless space. The molding used can be simple stock, like the single-piece crown installed here by This Old House general contractor Tom Silva, or elaborate pieces built up from separate lengths of various profiles.

Installing crown is only slightly more complicated than running baseboard. The variety of different joints and saw cuts, including a coped corner joint, an outside miter, a square cut, and a scarf joint, are best done with a coping saw and power miter saw. With practice, you should be able to make tight, long-lasting joints.

To determine how much molding to buy, measure each wall, round up to the next foot, and mark those measurements on a plain-view sketch of the room you’re working in. If one wall measures within a few inches of the length of a full piece of crown, buy the next longer length. When the wood arrives at the site, number the back of each piece with a pencil to correspond with the numbers indicated on your plan-view drawing.

The first piece installed will be square-cut on each end. Each subsequent piece will typically have one end that is square cut and another end that is coped or mitered. In some cases, the end opposite the cope will have to be mitered to helpmake an outside corner. When a length of molding is coped on one end, cut the coped end first. Once the coped end fits tightly, mark and cut the opposite end, whether it’s a miter or a square cut.

1. Lay out the molding

• Determine the order in which each piece of molding will go up around the room by drawing a plan view of the room on paper. To avoid having to cope both ends of the last length of molding, install the outside corner last. Otherwise, number each wall counterclockwise, starting with the one opposite the door.

• Hold a scrap piece of molding in place at each inside and outside corner and mark the position of its bottom edge—the edge that will sit on the wall—with a pencil. Stretch a chalk line between the marks at each corner and snap lines along the wall. This is the installation line.

• Locate studs and joists. Mark their locations with a pencil just below the installation line.

2. Install the first length

• Measure the wall for the first molding piece. Transfer this measurement to the wood, then use a power miter saw to cut the molding square at each end.

• Align the wood with the chalk line from Step 1. Working from the center, drive 8d finish nails through the molding—½ inch from the bottom edge and ½ inch from the top edge—into each stud and joist. Near the ends, drill 1/16-inch pilot holes for 4d or 6d finish nails.

• If necessary, splice two pieces with a scarf joint centered over a stud. Set the saw to a right-hand 45-degree setting. Hold the first molding piece to the right of the blade, and cut. Hold the adjoining piece to the left of the blade, and cut. Pilot a hole in the overlapping molding, ½ inch to the side of the joint, and attach with 6d finish nails.

3. Cut inside corner joint

• Coping is the process of cutting the end of a molding to mimic the profile milled into its face. Coped cuts are used where one piece of crown molding meets another at an inside corner.

• Place a length of crown upside down on the miter saw so that the molding’s bottom edge—the edge that will sit on the wall—rests against the fence, and the top edge—the one that goes on the ceiling—rests against the table.

• Set the saw to 45 degrees; swing the saw left for a left-side coped corner, and vice versa for a right corner. When you make the cut, the long point of the miter should be on the back of the molding, not on the face.

4. Highlight cut line with pencil

• After mitering the end of the crown molding, use a pencil to mark the edge on the face of the miter cut. This easy-to-see highlight will serve as your coping-saw cut line.

5. Cope inside corner joint

• To create a snug-fitting joint, hold a coping saw at a 5-degree angle away from the face of the molding and carefully cut along the pencil-marked edge. Check for a tight fit by bringing the molding to the wall and sliding it into place. If necessary, use a wood rasp or utility knife to pare away excess wood.

• Before attaching the piece to the wall, determine if its uncut end will land at an inside or outside corner. For an outside corner, proceed to Step 6. For an inside corner, measure from the top edge of the first piece you installed (Step 2) to this corner. Transfer that measurement to the coped molding by hooking the measuring tape on its top edge. Mark the length to the inside corner. Using the miter saw, make a square cut on that mark and nail the molding up, as in Step 2.

6. Mock-up an outside corner

• To measure a coped piece of molding that ends at an outside corner, make a mock-up of the corner from two 12-inch-long molding scraps. Make an outside miter cut on one piece, as in Step 3. Repeat this process for the second scrap piece, but rotate the saw blade to the opposite 45-degree angle. Glue and nail the pieces ends together.

• Hold the mock-up in place and mark the ceiling where the two pieces of molding come together.

• Measure from the top edge of the first piece you installed (Step 2) to the ceiling mark. Transfer that measurement to the coped length of molding (Step 3). Swing the saw back to its original 45-degree position and cut the molding to length.

7. Installing an outside corner

• If the other side of the corner will butt into an inside corner that does not require a coped end, first repeat the measuring and cutting sequence to complete the outside corner, making sure to rotate the saw blade to the opposite 45-degree angle. Then measure for and cut the butt end. Align the piece on the wall, spread glue on the surfaces of the miter, and nail the molding into place as in Step 2, fastening the corners together as you did on the mock-up.

• If the other side of the corner will butt into an inside corner that does require a coped end, repeat Steps 3-5 first, then complete the outside corner as above.

8. Cutting and fastening a return

• Continue working around the room, coping inside corners and mitering outside corners.

• If the ceiling height changes and the molding must end in the middle of a wall, cap it with a return. First, make an outside miter cut, as in Step 6, at the point where the ceiling height changes. Then, take a molding scrap at least a foot long and cut an outside miter on its end. To make the wedge-shaped cap, set the saw to 90 degrees and hold the scrap with its back flat on the saw table, cutting the piece so that it comes to a point at the bottom edge. Avoid splitting the small piece by gluing the return in place rather than nailing it.

[via This Old House & David Carmack]