TECHNICAL NOTE number 
 
 233 
 
 UNITED STATES DEPARTMENT OF AGRICULTURE 
 
 FOREST PRODUCTS LABORATORY 
 MADISON 5. WISCONSIN 
 
 — 
 
 FOREST SERVICE 
 August I960 
 
 APPROXIMATE AIR-DRYING AND KILN-DRYING 
 
 PERIODS FOR 1-INI 
 
 ^ DEPOSITORY 
 
 The air-drying periods for 1-inch lumber given in table 1 are based on 
 climatic conditions for the region in which the particular species is cut. 
 The periods apply particularly to hand-stacked piles varying in width 
 from 6 to 1 6 feet. Lumber in unit packages, commonly about 4 feet 
 wide, piled by machine would presumably dry in shorter periods. The 
 minimum periods given apply to lumber piled during the good drying 
 weather, generally during spring and summer. Lumber piled too late 
 in the period of good drying weather to reach 20 percent moisture con- 
 tent, or lumber that is piled during the fall or winter, will not reach a 
 moisture content of 20 percent until the following spring. This accounts 
 for the maximum periods given in the table. Local yard and weather 
 conditions and yard layout should be considered as well as general sea- 
 sonal factors in estimating the periods required for air drying. 
 
 In the portion of the table devoted to kiln drying, the minimum periods 
 represent the fastest drying reported in forced-air-circulation kilns. 
 Sometimes quality is sacrificed in favor of fast drying. Where the pro- 
 duct requires uniformly dry, stress -free lumber, longer drying periods 
 may be necessary. 
 
 Although table 1 lists kiln-drying periods for lumber greenfrom the saw, 
 the hardwoods are generally air dried to some extent before kiln drying. 
 Softwoods that are kiln dried are loaded into the kiln greenfrom the saw. 
 Factors affecting the period required for kiln drying are type of kiln, 
 quality or standard of drying, width of stock, type of sawing (plain or 
 quartered), moisture content, and preponderance of heartwood or sap- 
 wood. The time required for kiln drying, as might be expected, also 
 varies with the product being manufactured, some products requiring 
 low moisture contents, uniformity of dryness and stress -freeness, and 
 others requiring a somewhat lower quality of drying. 
 
The drying periods given in table 1 apply only to 1-inch lumber. The 
 increase in drying time for thicker stock is theoretically nearly pro- 
 portional to the square of the thickness but commercial experience 
 indicates it is somewhat less than this. 
 
 A list of Laboratory publications that give information on the seasoning 
 of lumber is available on request. 
 
 80729 F 
 
Table 1 . -- Approximate drying periods for 1-inch lumbei 
 
 Species 
 
 Days required to -■ 
 
 Air dry 
 4/4 green 
 stock to 
 20 percent 
 
 Kiln dry 4/4 stock from 
 
 20 percent 
 to 6 percent 
 
 Green to 
 6 percent 
 
 HARDWOODS 
 Alder, red 
 Apple 
 
 Ash: : 
 
 Black : 60-200 : 
 
 White : 60-200 : 
 
 Aspen (quaking and : 
 
 bigtooth) : 50-150 : 
 
 Basswood : 40-150 : 
 
 Beech : 70-200 : 
 
 Birch: 
 Paper . , 
 Yellow, 
 
 : 70-200 : 
 
 Buckeye, yellow : : 
 
 Butternut : : 
 
 Cherry, black : 70-200 : 
 
 Chestnut : 60-150 : 
 
 Chinquapin : : 
 
 Cottonwood, black : : 
 
 Dogwood : 
 
 Elm: 
 
 American 
 Rock . . . 
 
 3-5 
 4-7 
 
 5-7 
 4-7 
 
 3-5 
 3-5 
 5-8 
 
 50-150 : 
 
 5-8 
 
 5-8 
 
 5-8 
 
 5-7 
 
 4-8 
 
 7-12 
 
 4-8 
 
 5-8 
 
 4-6 
 5-8 
 
 6-10 
 10-15 
 
 10-14 
 11-15 
 
 6-10 
 
 6-10 
 
 12-15 
 
 3-5 
 11-15 
 
 12-16 
 
 10-15 
 
 10-14 
 
 8-12 
 22-28 
 
 8-12 
 12-16 
 
 10-15 
 13-17 
 
 (Sheet 1 of 4) 
 
Table 1. — Approximate drying periods for 1-inch lumber— (continued) 
 
 Species 
 
 Days required to — 
 
 Air dry 
 4/4 green 
 stock to 
 20 percent 
 
 Kiln dry 4/4 stock from -■ 
 
 20 percent 
 to 6 percent 
 
 Green to 
 6 percent 
 
 HARDWOODS (con't) 
 
 Hackberry : : 
 
 Hickory : 60-200 : 
 
 Holly : : 
 
 Hophornbeam (ironwood) : : 
 
 Laurel, California : : 
 
 (Oregon myrtle) : : 
 
 Locust, black : : 
 
 Madrone : : 
 
 Magnolia : 40-150 : 
 
 Mahogany : 60-150 : 
 
 Maple: : : 
 
 Silver (soft) : : 
 
 Sugar (hard) : 50-200 : 
 
 Oak: : : 
 
 California black. . . . : : 
 
 Live : : 
 
 Lowland : 100-300 : 
 
 Red : 70-200 : 
 
 Tan : : 
 
 White : 80-250 : 
 
 Osage-orange 
 Persimmon. . . 
 
 4-6 
 4-12 
 5-8 
 5-8 
 
 5-7 
 
 5-8 
 
 8-11 
 
 4-6 
 
 4-7 
 
 4-6 
 5-8 
 
 6-10 
 
 5-10 
 7-12 
 6-12 
 
 5-8 
 
 5-8 
 
 7-11 
 7-15 
 12-16 
 12-16 
 
 10-15 
 12-16 
 15-20 
 10-15 
 12-15 
 
 7-13 
 11-15 
 
 25-35 
 30-40 
 
 16-28 
 24-30 
 20-30 
 
 12-16 
 
 12-16 
 
 (Sheet 2 of 4) 
 
Table 1. — Approximate drying periods for 1-inch lumber— (continued) 
 
 Species 
 
 Days required to -- 
 
 Air dry 
 4/4 green 
 stock to 
 20 percent 
 
 Kiln dry 4/4 stock from 
 
 20 percent 
 to 6 percent 
 
 Green to 
 6 percent 
 
 HARDWOODS (con't) 
 
 Sweetgum: : 
 
 Heartwood : 70-300 
 
 Sapwood : 60-200 
 
 Sycamore 
 
 Tupelo: 
 
 Black : 70-200 
 
 Water : 70-200 
 
 Baldcypress : 100-300 
 
 Cedar : : 
 
 Alaska yellow : 
 
 Eastern red : 
 
 California incense . . : 
 
 Northern white : 
 
 Port Or ford white . . . : 
 
 Atlantic white : 
 
 Wes tern red : 
 
 Douglas-fir: : 
 
 Coast type : 20-200 
 
 Intermediate type . . . : 
 
 Rocky Mountain type . : 
 
 8-12 
 5-7 
 
 4-7 
 
 4-6 
 5-7 
 
 Walnut, black : 70-200 : 5-8 
 
 Willow, black : : 5-8 
 
 Yellow-poplar : 40-150 : 3-6 
 
 SOFTWOODS 
 
 4-8 
 
 2-3 
 
 15-25 
 10-15 
 
 6-12 
 
 6-10 
 6-12 
 
 10-16 
 
 12-16 
 
 6-10 
 
 10-20 
 
 4-6 
 6-8 
 3-6 
 8-10 
 4-8 
 8-10 
 10-15 
 
 2-4 
 4-7 
 4-7 
 
 (Sheet 3 of 4) 
 
Table 1 . —A pproximate drying periods for 1-inch lumber- (continued) 
 
 Species 
 
 Days required to — 
 
 Air dry : Kiln dry 4/4 stock from -- 
 4/4 green: 
 
 stock to : 20 percent : Green to 
 20 percent: to 6 percent : 6 percent 
 
 SOFTWOODS (con't) 
 
 Fir: 
 
 Hemlock: : 
 
 Eastern : 
 
 Western : 60-200 
 
 Engelmann : 20-120 
 
 Sitka : 40-150 
 
 UNIVERSITY OF FLORIDA 
 
 3 1262 09216 7476 
 
 Alpine : : : *~\ 
 
 Balsam : : ; 
 
 Grand ( lowland : • : 
 
 white) : : ; 
 
 Noble : : ; 
 
 Pacific silver : • : 
 
 Red : : | 
 
 White : : : 
 
 3-5 
 3-5 
 3-5 
 3-5 
 3-5 
 
 3-5 
 3-5 
 
 Larch, western : 60-120 : ! 
 
 Eastern white : 60-200 : 2-3 4-6 
 
 Lodgepole : : : " 
 
 Ponderosa : 15-150 : : 
 
 6-8 
 
 Red : ' 
 
 Southern yellow : : 
 
 Loblolly : 30-150 : '• 
 
 Longleaf : 30-150 : '• 
 
 Shortleaf : 30-150 : ■ 
 
 Sugar : : 
 
 Light : 15-90 : : 
 
 Sinker : 45-200 : ■ 
 
 Western white (Idaho) : '• : 
 
 3-5 
 3-5 
 
 3-4 
 
 5-10 
 
 3-5 
 
 *££' • 60-185 I 3-5 ': 10-14 
 
 Sinker'. '.. : 200-365 : 5-7 : 20-24 
 
 Spruce: : : . , 
 
 Eastern : 90-200 : y £« 
 
 .......: 4-7 
 
 Tamarack (eastern larch) : : : '"* 
 
 (Sheet 4 of 4)