Lumber can be notoriously mobile, especially during its first year inside a house. As the lumber dries, it shrinks across the grain. Other forces also hard at work include uneven grain, stresses that were built up in the living tree, and the loads imposed on the wood in its new role as dimensional lumber. As a result, studs and joists can bend, bow, twist, and cup—even after you've built a wall that was flat and plumb.
Ideally, you want to wait as long as possible after framing to begin drywall installation so the wood has a chance to acclimate. But if you have to rush, time spent checking and correcting framing problems will pay big dividends.
Although studs can often be straightened, the procedure is sometimes more trouble than it's worth. Ripping out the deformed stud and replacing it can be the most efficient solution. Another strategy, called sistering, involves installing a new stud next to the bad one.
As a quick check, hold a straight piece of lumber horizontally and diagonally across the studs to check that their edges are in the same plane. A stud that's bowed outward makes the test board rock; an inward bow shows daylight between the stud's edge and the test board.
If the stud bows outward, mark the edge of the stud with the amount to remove. Saw, plane, or chisel away the waste until the face of the stud is flat and in the same plane as its neighbors.
Fill in the hollow of an inward-bowed stud with shims. Check your progress with a straightedge held against the face of the stud. Thin shims let you achieve near-perfect alignments.
Editor's Tip for Thin Shims: To remove the last 1/16 inch of misalignment, buy a few squares of inexpensive self-adhesive floor tiles. Cut them into strips 1-1/2 inches wide and press them into position.
If the stud bows to the side, force it into position with blocking that bridges at least the next two studs on each side. Staggering the blocking up and down makes it easy to drive nails or screws into the ends. Install the blocking into the neighboring studs first, reinforcing them against the strain of straightening.
If you're working around a twisted wooden stud, coax it into alignment with a jumbo adjustable wrench or a special tool that's made for tweaking lumber into position. To ensure that the stud won't return to its old ways, drive some additional fasteners at the top and bottom and add blocking to the two neighboring studs.
Check each door opening to make sure that it's not cross-legged, an out-of-plane condition that make door installation very difficult. Diagonal strings from nails at the corners should just touch at the center. If the lines don't touch or press against each other, use a sledgehammer against the soleplate to nudge one or both walls into alignment. Getting the wall absolutely plumb is ideal, but if you have to compromise between flat and plumb, choose flat.
Use this procedure only on studs in nonload-bearing walls. Slice a kerf into the middle of the inward arc, cutting halfway to two-thirds through the stud. Drive a wedge into the kerf, pushing the stud straight. Reinforce the stud with 4-foot lengths of 1x4s (called scabs) nailed or screwed to both sides of the stud.