Warp reduction of SYP lumber by restrained drying

Warp in dimension lumber is a significant cause for loss in grade and value. Among dimension lumber, the 2- by 4-inch size is typically the most susceptible to warp for a variety of reasons. Among the various sizes of southern yellow pine (SYP) dimension lumber, 2 by 4 is produced in the greatest volume. Two-by-four material sawn from young trees, thinnings, and stem tops contains a significant proportion of juvenile wood and is particularly notorious for warp. At the planer mill, warped 2 by 4's represent a significant loss in value. In-service replacement of warped 2 by 4's as wall studs or truss members is costly. In this research, a drying restraint system was evaluated as a means of warp reduction in 8- and 16-foot-long SYP lumber. Both restrained and control boards were dried to approximately 9 percent moisture content, representative of final in-service conditions. The lumber was then measured for crook, bow, and twist. Results showed a significant improvement in higher grade recovery for the restrained material. As a means of assessing long-term dimensional stability, the 16-foot-long restrained package was remeasured for warp after both 1 and 9 months of warehouse storage.