Wood Handbook, Wood as an Engineering Material

heated above 49 °C (120 °F). Commercial air-dry stock gen-

erally has an average moisture content low enough for rapid

kiln drying or rough construction use. Moisture content is

generally in the range of 20% to 25% for dense hardwoods

and 15% to 20% for softwoods and low-density hardwoods.

Extended exposure can bring standard 19- and 38-mm

(nominal 1- and 2-in.) lumber within one or two percentage

points of the average exterior equilibrium moisture content

of the region. For much of the United States, the minimum

moisture content of thoroughly air-dried lumber is 12% to

15%.

Kiln Dry

Kiln dry means lumber that has been dried in a kiln or by

some special drying method to an average moisture content

General Technical Report FPL–GTR– 190

Figure 13–8. Surface checking on white oak

5/4 lumber.

Figure 13–9. End checking in red pine logs.

Figure 13–10. Severe collapse in western redcedar.

Figure 13–11. Red cedar timber end shows honey-

comb (top). Surface of the timber shows no honey-

comb (bottom).

Figure 13–12. Large knot in treated Southern Pine.