The question arises, naturally, how to recognize any grade of lumber after you have ordered it. The answer is "grade marking." This plan, developed largely through the efforts of the National Committee on Wood Utilization and the National Lumber Manufacturers' Association, has for its purpose the stamping of each piece of lumber with the mark identifying its species and grade. The plan has been pushed aggressively by the more progressive manufacturers and their associations, and to-day grade-marked lumber is an actuality; it is obtainable in most species and grades and in any locality, although as yet it is not always carried in retail stock. Grade-marking is the consumer's best protection, although lumber as now furnished under "certificates of inspection" from recognized lumber manufacturers' associations will be equally reliable as to species and grade.
Thorough seasoning or drying of lumber is probably the most essential factor in obtaining satisfactory results from wood construction. Dry lumber should be demanded - but after it is received on a job, it should be protected from the weather. This is especially true of millwork.
Shrinkage in wood is caused by moisture drying out of the wood fibers, and expansion or swelling is caused by the fibers absorbing moisture. Obviously, if wood before being installed is dried or "seasoned" to the average moisture content that it will have in the building, the subsequent shrinkage will be minimized and, in fact, practically unnoticeable. Lumber for framing and exterior uses should be seasoned to a moisture content of from 14 to 18 per cent, while wood for interior uses such as trim, flooring, or paneling should be kiln-dried down to about 8-10 per cent. Moisture content is the ratio of the weight of moisture (and other volatiles) in the wood to the oven-dry weight of the wood.
Dry lumber will not decay. Decay in wood is caused by attack of fungi which require air, warmth, and moisture. Dry lumber will not support fungus growth - one excellent reason, aside from its lack of shrinkage, for insisting upon its use in building construction.
When wood is used near the ground, or when subjected continually to moisture and dampness, as in the sills on the foundation wall, heartwood of the more durable woods should be specified, or else the material should be treated with a proved preservative such as creosote, zinc chloride, or other salt. The use of wood thus treated was formerly confined to bridges, wharves, and other heavy-duty services. During the past eighteen months, however, the National Committee on Wood Utilization has assisted in having treated lumber made available throughout Ohio and elsewhere for those parts of residence and light-frame construction mentioned above.
In specifying lumber, care should be taken to refer to the latest grading rules of the lumber manufacturers' association under which the particular kind of wood desired is produced. In addition, insist upon grade-marked material to be assured of quality.
For further information the reader is referred to Light Frame House Construction, Wood Construction, and other publications by the National Committee on Wood Utilization, U.S. Department of Commerce.