Based on SPIB Grading Rules

Southern Pine grading rules restrict moisture content of lumber 2″ and less in thickness to a maximum of 19%. If specified as “KD,” “KD19,” “dry” or “air-dried” the maximum is 19%. If specified as “KD15” (kiln-dried) or “MC15” the maximum is 15%. Material identified by a certified grade mark is evidence that Southern Pine has been properly seasoned.

Moisture content restrictions apply at time of shipment, as well as time of dressing if dressed lumber is involved, and at time of delivery to the buyer unless shipped exposed to the weather.

Items (Nominal thickness)	Kiln-Dried	Dry
D and Better Grades 1" and 1-1/4"	Max. 12% on 90% of pieces 15% on remainder	15%
1-1/2", 1-3/4" and 2" Over 2", but not over 4" Over 4"	15%	18%
	15%	19%
	18%	20%
Paneling	12%	12%
Boards1	19%	19%
Dimension1,2	19%	19%
Decking3	19%	19%
Timbers2	20%	23%
* Lumber dressed at a moisture content within the limits of these rules is sufficiently stabilized for most uses, but limited size changes will occur from shrinkage or expansion if the moisture content is further reduced or increased after dressing. The normal shrinkage allowance is 1% reduction in size for each 4-point reduction in percentage of moisture content and same tolerance for any expansion. (1) KD15 or MC15 may be specified if desired. (2) Moisture content provisions must be specified for material 2-1/2" and thicker because seasoning is not mandatory for these sizes. (3) All thicknesses of roof decking should be specified at 15% maximum moisture content.