Inspect the attic area and determine how many pieces of lumber will be needed for installation. If you only are going to brace a small section, a single 6-foot piece of two-by-four may be sufficient. If you want to brace a larger section, more pieces will be needed.
Use a tape measure to measure the distance between the rafter, or rafters, that will be braced and the floor joist.
Set the two-by fours on two saw horses and mark the measurements needed for the braces. Saw the beams to the size needed for the braces.
Place the top of the brace against the side of the rafter and hammer it into place with the framing nail. Hammer the bottom end of the wood brace to the bottom floor joist. Continue this process until all the braces needed are in place.