High-Temperature Drying of Douglas-Fir Dimension Lumber

Douglas-fir dimension lumber (2 by 4, 2 by 6) was dried by three categories of kiln schedules–conventional temperature, elevated-high temperature, and high temperature with and without restraint. The objectives were to determine relative drying times and suitability of the material for house construction in Japan. Relative times for drying plus equalizing were: conventional–100; elevated-high– 33; high temperature– 23. Thickness shrinkage was slightly less for conventional drying. There was no apparent trend in width shrinkage. Surface checks and splitting caused no problems, but end checking penetrated deeper with increasing temperature. Twist, crook, and bow were not significant. Some brown discoloration occurred with elevated-high and high temperature drying, but the discoloration was superficial. The lumber studied would not be significantly degraded under the applicable Japanese Agriculture Standard. Considering drying time and defects only, commercial high temperature drying of Douglas-fir dimension lumber (upper grade) could be established by the schedules suggested.

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