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How to Install Three-Piece Crown Molding

Layer stock moldings onto a box beam to create a budget-friendly custom profile.

A common decorative flourish for traditional homes, crown molding enriches a space by forming an eye-catching transition between the walls and ceiling. But if your ceilings are high or your room has generous moldings around windows and doorways, a single strip of crown molding might get lost overhead. To get the right effect, you could opt to use a large-profile molding, says This Old House senior technical editor Mark Powers. "But you'll pay a hefty price for large profiles," he says. To lower the cost without sacrificing aesthetics, Mark came up with a way to install a simple L-shaped half beam first, then attach crown moldings to the fascia and soffit for a handsome, built-up appearance. Recruit a buddy to help you make cuts and lift the bulky pieces into place, and in just a couple of days, you'll have pulled off a room transformation that will draw all eyes upward.

Upper crown molding: Classical Craftsman Collection Crown, WOCM005.

Fascia board: Classical Colonial Collection Crown WOCM002. Both from WindsorONE.

Lower crown molding: AB405 3⅛-inch crown; Ring's End

How to Install Three-Piece Crown Molding Overview

Illustration by Gregory Nemec

Project timeline

  • Friday: Mark the room's framing, and install the cleats.
  • Saturday: Assemble and install the half beams and backing blocks.
  • Sunday: Lay out the cuts, and cut and install the upper and lower crown moldings.

Step 1: Mark the Cleat Locations

Photo by Wendell T. Webber

Determine the inside height and depth of the half beam. Add ⅛ inch to both numbers and cut a scrap block to this size. Clip the block's corner, as shown, so that it will clear imperfections where the walls and ceiling meet. Use the block to mark the half beam's position near the ends of each wall. Snap a chalk line between each set of marks.

Step 2: Attach the Cleats

Photo by Wendell T. Webber

To mark the room's framing, affix painter's tape to the walls and ceiling, as shown, so that it won't be covered up as you work. Use a stud finder to mark the stud and joist locations on the tape. Affix 2x2 cleats to the framing using 3-inch screws. The cleats should lie inside the chalk lines toward the junction of the walls and ceiling, as shown. Where the ceiling's cleats are parallel to the joists, use toggle anchors for a secure installation. Mark their locations by driving 3-inch screws through the cleats and into the ceiling. Remove the cleats, drill larger holes in the ceiling where the screws penetrated it, and fit anchors into them. Reattach the cleats, driving 3-inch screws through the holes and into the anchors.

Step 3: Cut the Parts and Attach Nailing Strips

Photo by Wendell T. Webber

Measure the length of each run and cut fascia and soffit boards to size. If the fascia has a decorative edge, miter the ends of the boards to make the edges match up. The soffits should be mitered first: Make the cuts across their widths so that the long points will rest on the wall for inside corners and the short points will rest on the wall for outside corners. Then bevel the ends of the fascia across their thicknesses to follow the angled ends of the soffits.

Next you'll add nailing strips to keep the attachment of the fascia and soffit square. Cut 1x1 strips for the fascia to size. On the back of each fascia, draw a line 1¾ inch from the decorative edge so that there's room for a reveal when the soffit is installed. Use wood glue and 1¼-inch nails to affix the strip to the fascia along the line.

Tip: When attaching the nailing strip, nail through one end first and hold the strip to the line as you drive nails along the strip's length. This technique will remove any natural bowing in the strip.

Step 4: Join the Soffit and Fascia

Photo by Wendell T. Webber

Apply glue along the seam between the strip and the fascia, on the side with the decorative edge. Set the soffit in place. Drive 1-inch nails through the soffit and into the strip.

Step 5: Attach a Connecting Block

Photo by Wendell T. Webber

This will help join the half beams at the corners. Place a scrap block on the back side of the soffit so that it extends past the cut edge as shown, and attach it with 1¼-inch screws. Repeat these steps for the remaining half beams.

Step 6: Put Up the Half Beams

Photo by Wendell T. Webber

Countersink pilot holes every 12 to 16 inches through the fascia and soffit. Lift the half beam into place, and drive 2-inch screws through the pilot holes and into the cleats. (Since you added ⅛ inch to the marking block in Step 2 to clear wall imperfections, there may be gaps between the beam and the walls or ceiling. These will be covered when the molding is installed.) Repeat for the adjoining half beam. Connect the beams by driving 1¼-inch screws through the end of the second beam's soffit and into the connecting block on the first beam. Repeat for the remaining half beams.

Step 7: Attach Backing Blocks

Photo by Wendell T. Webber

Cut the blocks. (Learn how to cut filler blocks for the nailing surface.)

Glue the blocks in place and drive 2-inch nails through them and into the fascia and ceiling with the angled sides facing out.

Step 8: Cut the Crown Molding

Photo by Wendell T. Webber

Map the molding's installation, marking a miter, cope, or square cut at the end of each run. An inside corner is formed from a coped end abutting the face of a square-cut piece that dead-ends in the corner of the room. For a tight fit, avoid runs with two coped cuts. (An outside corner is formed from two mitered ends; you'll make those cuts in Step 15.) See this illustration for common crown molding cuts and joints. Learn how to cut molding for an inside corner. Then watch a video of Tom Silva using different kinds of saws to make miter cuts.

Before making cuts, hot-glue a horizontal fence to your saw deck to help the molding stay in place. (Learn how to make a guide fence.) To prepare the end of a molding for coping, you'll give it an open-miter cut to expose the profile's face. When using a regular miter saw, always position the molding upside down on the saw so that the miter cuts will be backward.

When you're done cutting the upper molding, pull off the horizontal fence and secure a new one to the saw for the lower molding to account for its different profile.

Step 9: Prepare the Ends for Coping

Photo by Wendell T. Webber

Hold a pencil with the lead resting against the open-mitered face of the molding. Darken the edge of the profile as shown.

Step 10: Cope the Ends

Photo by Wendell T. Webber

With a coping saw, carefully back-cut the molding, following its profile as shown. Read instructions on how to make a cope cut and watch a video of Tom Silva making cope cuts.

Tip: Always cut the coped end of a piece of molding first, then cut the opposite end of the board to length. That way, if your cope cut isn't perfect, you can redo it without wasting the piece.

Step 11: Install the First Run

Photo by Wendell T. Webber

On the fascia, mark a line where the lower edge of the upper molding should fall. Position the first run of molding along this line, and butt its square-cut end against the corner. Drive 2-inch nails through the molding and into the fascia, then drive 2-inch nails through the molding and into the joists or backing blocks. Don't add nails within the last few feet of the coped end in case adjustments are needed when the adjoining run is installed.

See a typical sketch for laying out crown molding in a room.

Step 12: Build an Inside Corner

Photo by Wendell T. Webber

Butt the coped end of the adjoining run of molding against the face of the square-cut end you just installed. If needed, add shims to create a tight joint between the pieces. Drive nails next to (not through) the joint to secure the pieces, and nail the rest of the molding in place as you did in Step 12. Repeat all steps for lower crown molding, nailing it to the wall and soffit.

Step 13: Mark the Corners

Photo by Wendell T. Webber

To mark the miter cuts for outside corners, you'll first mark the ceiling for the upper molding (and the soffit for the lower molding, as shown) to see where the ends of the pieces will land. Position a scrap piece of molding in place so that one end extends beyond the corner. Trace a light pencil line onto the ceiling (or soffit) along the top edge of the molding, extending the line past the corner. Repeat for the other side to create a set of crosshair marks. Position the length of molding to be installed along this line and the fascia (or wall) so that one end extends beyond the corner. On the face of the molding, mark the spots where the top edge meets the crosshair line and the bottom edge meets the corner. Draw a cutline on the face of the molding between these marks. Repeat for the other side.

Step 14: Cut and Install the Moldings

Photo by Wendell T. Webber

Miter the ends of the moldings. Learn how to cut molding for an outside corner. The long point of each miter should be on the top edge of the molding. Position the first piece of molding so that the long point sits on the crosshair, and nail it in place. Position the second piece to create a tight corner joint with the first, and nail it in place.

Step 15: Cut a Scarf Joint

Photo by Wendell T. Webber

On long runs that require two lengths of molding, an angled scarf joint minimizes the seam between the pieces. For a tight fit, adjust your layout so that the joint will land just past a stud or joist, or on a backing block. Cut the ends of the molding at parallel 30-degree angles. The first piece to be installed should have an open miter with a longer back side and a shorter face, as shown. Position the piece with the open miter on the wall and nail it in place to the framing, but don't add nails within a few inches of the scarf cut for now. Apply glue to the cut end.

Step 16: Install the Scarf Joint

Photo by Wendell T. Webber

Fit the second piece of molding into place. Nail through the molding near (not through) the joint and into the framing, angling the nail gun slightly toward the joint to tighten the fit.

Step 17: Finish the Runs

Photo by Wendell T. Webber

Work around the room until all molding is installed. Remove the painter's tape from the walls and ceiling. Caulk nail holes, joints, and seams. Lightly sand the assembly with a fine-grit sanding sponge, and finish by applying two coats of semigloss paint.