Dimensional lumber framing is never perfect because it warps when as it dries. Whoever is preparing the wall for drywall or tile finishes must figure out a way to get the studs flat and in plane to ensure a good finished surface. Furring strips are placed on the face of the 2x4 or 2x6 stud, offsetting any discrepancies in the straightness of the framing. Sister studs are attached to the side of an existing stud to create a straight and inplane stud. Cardboard shims are usually stapled to the face of a stud similar to a furring strip and are good for small discrepancies up to 1/4".
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