How to Box-In Duct Work in a Basement

Measure the length, height and width of the duct you want to cover with a measuring tape. Write these measurements on a piece of paper with a pencil.

Measure four sections of 2-by-4-inch pressure-treated lumber to the length of the duct and mark the measurement with a pencil. Cut the lumber to length with a circular saw. These sections form the top and bottom frame plates for the soffit's sides.

Measure and cut sections of 2-by-4-inch lumber 1 inch shorter than the distance between the bottom of the ceiling joists and the bottom of the duct. These sections form the soffit studs. You need enough studs to place between the top and bottom frame plates for each side at 16-inch intervals.

Lay one top and one bottom plate on its 2-inch side, far enough apart to accommodate the studs. Place one stud between the plates at each end, and place interior studs at 16-inch intervals. Repeat this process with the remaining plates and studs.

Drill pilot holes through the top and bottom plates into the ends of each stud. Pilot holes, which are slightly smaller than the diameter of wood screw shafts, help you install wood screws more quickly. Insert 4-inch wood screws into each pilot hole and tighten them with a screwdriver to secure the soffit sides.

Install one soffit side by drilling pilot holes through the top plate into the ceiling joists on one side of the duct, then securing the top plate with 4-inch wood screws. Repeat this process for the other soffit side.

Measure the distance between the two bottom plates. Cut enough 2-by-4-inch lumber sections to this measurement to span the bottom plates at 16-inch intervals.

Place one of the lumber sections between the bottom plates at one end of the duct. Drill pilot holes and insert 6-inch wood screws through the bottom plates into each end of this lumber section. Repeat this process at the other end of the duct, then at 16-inch intervals between the ends.

Transfer the soffit side measurements to a piece of drywall. Snap a chalk line on the drywall to obtain straight lines, and cut the drywall along the measurement lines with a utility knife. Cut a second section of drywall to the same measurements.

Install one drywall section to each soffit side by driving 3-inch drywall screws through the drywall into each stud at 4-inch intervals. Cut a section of drywall to fit the bottom section of the soffit and attach it using the same process.

Finish the drywall by filling in the screw heads with compound and taping the corners with drywall tape.