How to Frame an Air Duct in a Basement

Measure 2 inches below the air duct on the wall closest to the air duct. Snap a chalk line along the wall at that height. Measure the length of the wall and cut a 2-by-4 board to match the distance. Position the board with the bottom edge even with the chalk line and nail it to the wall with 10d nails.

Cut two lengths of 2-by-2 board to match the length of the 2-by-4 you just installed. Measure down from the ceiling joist nearest to the air duct and determine the distance to a point even with the first chalk line you measured -- that is, 2 inches below the air duct.

Cut a series of 2-by-2 boards to match the distance noted in Step 2, less 1-1/2 inches. Place these between the two 2-by-2 boards from the previous step, like the rungs of a ladder and spaced every 8 inches. Place the final board even with the opposite end. Nail the structure together with 8d nails.

Place the structure against the side of the joist. Position it so the bottom edge is in line with the bottom of the 2-by-4 board on the wall. Nail the structure to the joist with 8d nails spaced every 8 inches.

Measure the distance between the inside edges of the 2-by-4 board and the structure. Cut a series of 2-by-2 boards to match this length. Mount the boards between the 2-by-4 and the structure spaced every 8 inches and nail them in place with 8d nails.

Finish the frame with drywall, wood or paneling.