When building a wall you must first ensure that it is straight and level. Without these two factors the wall and the structure around or within it will never be structurally sound. Whether you are constructing a new wall or you are checking the straightness of an existing wall, you will require a few basic tools and a good understanding of some basic principles to get the job done.
Hammer a small nail into the ceiling just next to your wall. Hang your plumb bob from the small nail so that it almost reaches the floor. You will use this plumb bob to check that your wall is straight from top to bottom.
Measure the gap between the plumb bob line and the wall at the top of the wall. Do the same at the bottom of the wall. If the two measurements are equal, the wall is straight up and down, if not then it is not. Remove the plumb bob and install it at the other end of the wall. Perform the same process to check the straightness of that end of the wall.
Locate a wall within your house that runs parallel to the wall in question. Place the end of your tape measure at the base of the parallel wall. Stretch the tape measure out to a distance about 3 inches short of the wall in question and mark the floor. Perform this process at both ends of the wall in question. Perform the same process along the ceiling and mark the two locations.
Snap a chalk line between the two marks you have made on the ceiling. Snap a chalk line between the two marks you have made on the floor. Check the straightness of your wall compared with the chalk lines. To be certain that the wall is straight use your tape measure to gauge the distance between the wall and the chalk line at several points throughout its length. If you are building a wall use these chalk lines as your guide.
Use along straight edge like an extended length level to make sure the interior portion of your wall is straight. Place the straight edge on the wall and hold it horizontally. If there are gaps anywhere between the wall and the straight edge your wall is not straight. The cause may be warped or faulty studs or framework beneath the surface of the wall.