How to Box in a Ceiling Support Beam Inside

Measure the length of the beam that is being covered. Also, measure the thickness of the beam as it hangs down from the ceiling, and add 2 inches to that measurement. The extra 2 inches creates a small buffer between the soffit and the beam.

Examine the location of the beam in the room, and determine if you want the soffit to extend to one of the side walls, or just cover the beam itself. If the beam is in the center of the room, covering just the beam can leave the space between it and the wall more open.

Mark a line on the side wall with a laser level or chalk line that is 2 inches below the bottom of the beam. Cut a 2-by-4 board that is the same length as the beam to the wall, placing it along the top edge of the line. Use masonry screws and a hammer drill if the wall is concrete. Drive stainless steel 2-inch screws through the studs if the wall is finished. If you're not extending the soffit to the side wall, skip this step.

Cut the rails for the side panels from 2-by-2 boards, using two rails for each side panel. If the soffit extends to the wall, you only need one side panel.

Measure and cut sheets of half-inch plywood that are the thickness of the beam plus 2 inches.

Attach the rails to the outer edges of the plywood sheets to construct the side panels. Drill 1 5/8-inch screws through the plywood and into the rails every 6 inches.

Lift the first side panel up to the ceiling, and drive 3-inch screws through the top rail and into the ceiling joists every 6 inches. Install the second side panel, if applicable.

Measure the distance between the inner edges of the side panel, or the inner edges of the side panel and 2-by-4 that's screwed to the wall. Cut strips of 2-by-2 boards, called lookouts, to this length. Cut enough lookouts so that they can be spaced no more than 16 inches apart.

Install the lookouts along the bottom edge of the soffit box. If the box has two side panels, drive a nail through the bottom rail on each side and into the end of the lookout. If the box runs to the wall, drive a nail through the rail of the side panel, and drive a nail through the lookout and into the 2-by-4 at a 45-degree angle.

Cut pieces of half-inch drywall to fit over the bottom of the box and the side panels. Do this by placing a straightedge against the cut line, then cutting a score line into the drywall with a utility knife. Snap the board at the score line.

Install the drywall onto the framing by driving drywall screws into the top and bottom rails on the side panels, and the lookouts and bottom rails (or 2-by-4) on the bottom edge. Use one screw every 8 inches, and drill them so that the screw heads lie just below the surface of the drywall. This makes the screws easier to conceal.

Nail metal corner bead to the edges where the side panels meet the bottom of the soffit.

Apply joint compound to the joints between the drywall sheets, and over the corner bead, using a putty knife. Place strips of drywall tape into the joint compound, then press the tape into the compound by running over it with the putty knife. Allow the joint compound to dry overnight.

Sand the surface of the soffit to smooth the areas where you applied the joint compound, and wipe the dust off of the soffit.

Add two more layers of joint compound and drywall tape to the soffit, following the same procedure you used when applying the first layer.

Apply a coat of primer to the soffit, and allow it to dry. Use smooth, even strokes when applying the primer, and take care to prevent it from beading up along the bottom edges of the soffit.

Cover the soffit with two coats of paint, applying it the same way you applied the primer. Allow the first coat of paint to dry before applying the second coat.