Early Development of Standards and Building Codes in the United States
While formal standards for grading can be found as early as 1754 in Europe (Shelley, 1992), published standards and grading rules in the United States were not produced until the early 20th century after timber test results began to be published. The American Society for Testing and Materials (ASTM) was formed in 1898 (Green and Evans, 2001) and marks the beginning of formal standards for testing that would ultimately lead to the standards we have today. In 1905, Committee Q (the Committee on Standard Specifications for the Grading of Structural Timber) was formed. This committee identification changed to its current form, Committee D7, in 1910.
While Committee D7 was organizing and working on the development of grading rules, the U.S. Forest Service (USFS) was also investigating how these rules might work in practice. In 1915, at the 18th Annual Meeting of ASTM, H.S. Betts discussed a potential set of grading rules developed by the USFS, based in part on the work of Cline and Heim (1912) and others mentioned above. Finally, in 1922, ASTM tentatively approved ASTM D143, Standard Methods of Testing Small Clear Specimens of Timber, which was formally established as a standard in 1927 (ASTM D143-27). A similar standard for testing full-sized timbers, ASTM D198-27 was also established in that year (Green and Evans, 2001).
In 1922, while ASTM was drafting the standards for testing, the Central Committee on Lumbers Standards, in the Department of Commerce (now the American Lumber Standards Committee, ALSC), was formed due to discussions between a committee formed by the National Lumber Manufacturer’s Association and Secretary of Commerce Herbert Hoover (Shelley, 1992). The ALSC produced “Simplified Practice Recommendation No. 16” as the first national standard for lumber sizes and grades in 1924. This standard focused on nomenclature, the visual properties of wood members, and standardization of sizes. It did not include any information on allowable design values (Shelley, 1992).
Information on allowable design values was first published as USDA Forest Products Laboratory Circular 295, “Basic Grading Rules and Working Stresses for Structural Timbers” (Newlin and Johnson, 1923). This circular outlined a system of grading similar to our current one, with four grades of lumber (S1 to S4) which were limited to 88, 75, 62 and 50 percent of the strength ratios of clear wood, respectively (Green and Evans, 2001). This system for grading and allowable design values contained values for approximately 40 different species. However, values were shown without regards for width or thickness of members, and there were no special rules for lumber four inches or less in thickness. A companion paper, USDA FPL Circular 296, “Standard Grading Specifications for Yard Lumber,” contained recommendations on sizes and moisture content adjustments (Ivory, et al., 1923).
With this promising start, ASTM went on to promulgate and improve upon numerous standards that today are the basis for grading and assigning allowable stresses to lumber and timber. The most important of these for grading of structural lumber and timbers in historic structures are:
- ASTM D 2555, Standard Methods for Establishing Clear Wood Strength Values. This standard was first issued as a tentative standard in 1966, then a full standard in 1969. It was developed to provide an “authoritative compilation of clear wood strength values for commercially important species” and marked the first use of the 5th percentile for deriving allowable wood properties.
- ASTM D245, Standard Methods for Establishing Structural Grades for Visually Graded Lumber. The original version, written as a tentative standard in 1926 and a full standard in 1927, was based on the work of Newlin and Johnson (1923) and focused on a means of selecting material for strength values.
Once test data were available and testing standards and procedures for grading lumber and timbers with defects were developed and established, the means to use the information for designing wood structures needed to be codified. Individual jurisdictions typically wrote their own building codes – New York City and Chicago are just two examples – however these codes listed basic design stresses for wood but often no criteria for defects that might be present in the lumber or timber.
Beginning in 1915, code-writing organizations were formed to address the need for building standards that safeguarded public health and safety. With the advent of the early building codes, Woolson, et al. (1926) made recommendations on working stresses (a form of design value) to the U.S. Department of Commerce. Betts and Helphenstine (1920, 1933) discussed lumber-grading procedures and T.R.C. Wilson (1934) produced a guide for the grading of structural timbers, USDA Miscellaneous Publication No. 185. A detailed summary of wood properties followed in 1935 by Markwardt and Wilson. These publications discuss early grading procedures and material properties, much of which may still be relevant and applicable to historic structures.
During the 1940s, as the country recovered from the depression and prepared for war, there was an interest in expanding design values to “yard” or dimension lumber (since previous research was focused on larger structural timbers). A supplement to USDA Miscellaneous Publication No. 185 was published, standards for stress grading of lumber were loosened, and grades were developed for lumber with less than a 50 percent strength ratio to that of clear wood (Shelley, 1992). This work culminated in recommendations by the National Lumber Manufacturers Association in 1944 known as the National Design Specification for Stress-Grade Lumber and Its Fastenings (1944). This document has evolved into the National Design Specification for Wood Construction (American Forest & Paper Association and American Wood Council, 2005).
During the 1950s and 1960, the most important debate in lumber standards was about the simplification and unification of size standards, a problem which had been ongoing since the inception of grading rules in the early 19th century. This problem was eventually resolved in the 1970s, when the American Lumber Standard (ALS) was revised as Voluntary Product Standard PS20-70 American Softwood Lumber Standard (Shelley, 1992). PS20-70 made substantive changes in lumber grading and marketing and established an independent Board of Review to enforce grading and grade marking portions of the standard. The Board of Review has authority to certify grading agencies and approve lumber design values promulgated by regional agencies in accordance with ASTM standards (Shelley, 1992). The ALSC is active today in establishing procedures for grading dimension lumber.
In a manner similar to the development of grading and lumber design values, building codes evolved from multiple sources. Eventually, there were three primary organizations that had responsibility for code writing. Each of these three organizations developed their own building code, which is used in specific zones of the U.S., generally covering geographic regions of the U.S. as stated below.
- Building Officials and Code Administrators International, Inc. (BOCA). This group was created in 1915, and administers the Standard National Code that was used in the eastern and Midwest portions of the U.S.
- International Conference of Building Officials (ICBO). Formed in 1922, this group’s code (the Uniform Building Code) was used in the western U.S.
- The Standard Building Code Congress International (SBCCI). This group was formed in 1941, and its code (the Standard Building Code) was developed for the southern states.
Recently, these code-writing organizations were consolidated into the International Code Council, Inc., which produces the International Building Code.