How to Support Trusses While Installing a New Window

Put on a pair of work boots.

Measure one 2-by-10-inch board and one 2-by-4-inch board to a length of 8 feet, using a tape measure. Mark the length with a pencil and cut the boards to size with a saw.

Locate the midpoint of each board, 4 feet from either end, using a tape measure. Mark the midpoint with a pencil.

Measure a distance of 3 feet from the wall in which you intend to install a window. Place the 8-foot-long 2-by-4 on the floor at this point.

Hold the 2-by-10 flat against the trusses directly above the 2-by-4, so the midpoints line up. Access the joists with a step ladder if necessary.

Attach the 2-by-10 to the trusses, using a drill and wood screws.

Measure the vertical distance between the 2-by-4 on the floor and the 2-by-10 attached to the joists with a tape measure.

Measure a distance equal to the vertical distance between the two boards on at least nine 2-by-4-inch boards, using a tape measure. Mark the length with a pencil and cut the boards to size.

Place one of the freshly cut 2-by-4-inch boards between the 2-by-4 on the floor and the 2-by-10 affixed to the joists, so the bottom and top of the board line up with the pencil marks drawn at the midpoint of floor and ceiling boards, respectively. Align the board so the thin side faces the wall in which you intend to cut a hole for the window.

Check to make certain the vertical 2-by-4 is perfectly vertical, using a level. Adjust the board if necessary. Move the 2-by-4 on the floor if necessary to adjust the location of the midpoint.

Drill wood screws through the vertical 2-by-4 into the boards on the floor and ceiling.

Install one 2-by-4 vertically at each end of the temporary support structure, using the same process.

Install more vertical 2-by-4-inch boards, moving in from the edges toward the center, about every 10 inches. Exact measurements are not necessary, since the structure provides only temporary support. Install the boards as you did previous boards.