Seasoning Requirements
Southern Pine
Seasoning Requirements
One of the qualities that makes Southern Pine lumber structurally superior as a building material is its seasoning requirements.
Southern Pine dimension lumber 2 inches thick or less must be dried to a maximum moisture content of 19 percent for optimal dimensional stability. This minimizes shrinkage associated with green lumber and provides long-term stability.
Grading rules restrict moisture content of Southern Pine lumber 2 inches thick or less to a maximum of 19 percent. If specified as “KD,” “KD19,” “dry,” or “air-dried,” the maximum is 19 percent. If Southern Pine lumber is specified as “KD15” (kiln-dried) or “MC15,” the maximum is 15 percent.
Material identified by a certified grade mark is evidence that Southern Pine lumber has been produced by following the proper seasoning requirements.
Moisture content restrictions apply at time of shipment and dressing, if dressed lumber is involved. They also apply when Southern Pine lumber is delivered to the buyer, unless shipped exposed to the weather.
Lumber dressed at a moisture content within the limits of these rules is sufficiently stabilized for most uses, but limited size changes – shrinkage or expansion – will occur if the moisture content is further reduced or increased after dressing.
The normal shrinkage or expansion allowance is a 1 percent reduction in size for each 4-point reduction in percentage of moisture content.
| Items (Nominal thickness) | Kiln-DriedKiln-Dried | Kiln-Dried |
|---|---|---|
| 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. |
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