How to Build a Door Mantle

Measure the distance between the outside edges of your door’s vertical casing or molding. Take the measurement at the top of the doorframe to ensure accuracy in case the frame isn’t perfectly square or plumb.

Cut a length of 1-by-4-inch frieze board to the exact width of the doorframe, using 90-degree angle cuts.

Use 90-degree angle cuts to trim a piece of 1 1/2-inch wide bullnose stop molding to a length that’s 3/4 of an inch longer than the width of the doorframe. This creates a crosshead strip with a 3/8-inch reveal.

Cut a length of 2 1/2-inch crown molding that is 6 inches longer than the width of the doorframe, using 90-degree angle cuts.

Cut a length of 1-by-3-inch top cap molding that is 6 3/4 inches longer than the width of the doorframe, using 90-degree angle cuts.

Center the crown molding along the top edge of the frieze board, so that 3 inches of molding extend beyond each of the board’s sides. Mark the bottom edge of the crown molding where it meets the frieze board.

Make 45-degree angle back-cut miters extending outward from your marks along the bottom of the crown molding.

Coat the bottom edge of the frieze board with a thin layer of wood glue. Center the glue-coated surface onto the backmost part of the topside of the strip of bullnose stop molding, ensuring that the back side of the molding and the back of the board are flush. The bullnose strip should extend 3/8 of an inch past each side of the board.

Drive 6d, or 2-inch, finishing nails at 3- to 4-inch intervals through the bottom of the molding strip into the frieze board.

Coat the top side of the frieze board with a thin layer of wood glue. Lay the unit on its backside.

Set the top cap molding on its backside. Center and butt the backmost part of the bottom side of the cap against the glued surface of the frieze board. The edges of the top cap should extend 3 3/8 inches beyond each side of the board.

Drive 6d finishing nails at 3- to 4-inch intervals through the top of the cap into the frieze board.

Center and butt the mitered piece of crown molding into the corner created by the frieze board and top cap, so that the bottom edge of the crown molding is flat against the board, and its top edge is angled toward the cap's front edge. Note where the crown molding comes in contact with the unit.

Remove the crown molding. Line its two contact points with wood glue, then press it back into place. Drive 6d finishing nails at 3- to 4-inch intervals along the bottom of the molding into the frieze board, and along its top into the cap.

Make a 45-degree angle front-cut miter on a piece of crown molding scrap. Cut the miter at an opposite angle to that of one of the mitered ends of the crown molding, so that the pieces fit together. Repeat the process with a second piece of scrap molding for the other side of the mantle, creating mitered returns that wrap the molding to the wall.

Fit each mitered return into place, marking them to length where they meet the back edge of the mantle. Remove the end pieces and trim them with a handsaw, making 90-degree angle cuts that will butt up against the wall.

Glue the mitered ends into place. Apply masking tape across the joints until the glue is dried.

Lightly sand the edges of the mantle. If desired, finish it to match the rest of the door’s trim.