Wait! Continue reading! It's really a fascinating topic. OK. It's probably not. But read it anyway!
Out here in Nevada we commonly come upon historic sites, usually mining related, that have wooden posts in various locations. Like everything else in archaeology we measure them. What do those measurements tell us? Do we measure them because, as archaeologists, we obsessively measure everything? Yes. And no. The measurements can tell us something.
Of course, we have to start by addressing the quality of the artifacts we are measuring. When we are measuring lumber and looking for a certain measurement it’s important to recognize whether the wood is heavily weathered or not. In these dry environments wood tends to crack and separate. Out here in Nevada, snow and rain can get in wood, freeze, and cause the wood to split. The measurement is virtually useless in a lot of those cases. You can sometimes still find a useful place to measure though. Look at the ends. Sometimes they haven’t split yet. Or maybe just one end hasn't split yet. Don’t give up. There’s always a way.
OK. So what is “dimensional lumber”. Basically, it’s lumber that has been dried, planed, and cut to a specific width and depth in inches. Common sizes found on sites are 2x4 and 4x4. Large 6x6 and 8x8 beams can be found as well. The common sizes, referred to as the “nominal” size, are based on the wood’s green, or rough, dimensions. The finished size is actually smaller than the nominal size. Table 1 illustrates nominal size versus actual size.
Prior to the late 1800s building lumber was usually processed close to where it was produced. As markets grew and lumber was needed further and further away from mills it became apparent that standard sizes would be needed. After 1870 some sawmills began to plane wood with machines to make rough lumber more uniform. The boards were usually only surfaced on one side, known as S1S, and sometimes on two sides, S2S. As late as the 1920s some mills based their pricing structure on rough, saw-sized dimensions. The reduced actual sizes of the dimensioned boards also meant a reduction in weight which resulted in a reduction in shipping costs. It always comes down to money.
The early 1900s brought regional sizing standards to the market. In 1902 the Pacific Coast Lumber Manufacturers Association Standard Dimensions and Grading Rules for Export Trade determined that boards under 4 inches and under in thickness or 6 inches under in width could be worked an eighth of an inch less for each side of the edge surfaced. In 1906 certain board sizes in North Carolina could be dressed by as much as an eighth of an inch. By 1919, after shortages associated with World War I, it was clear that national standards should be adopted. The 1919 meeting of the American Lumber Congress (yeah, that’s a real thing) determined that standards needed to be written for lumber sizes.
National standardization of lumber sizes began in 1921. Several major lumber Barons approached the Secretary of Commerce, Herbert Hoover, and proposed a standardization of lumber size and grading standards and requested that the standards be published by the Bureau of Standards. The first national standards didn’t come until after many more meetings and revisions. The date was November 6, 1923. Of course there were problems and the actual establishment of the standards didn’t take place until July 23, 1924.
Over the next few decades battles over how much a board could be dressed were fought, won, and lost. Lumber barons across the country all had their own agendas. Much of the controversy centered around money, of course. Lumber suppliers that used the Panama Canal to ship lumber wanted smaller boards because shipping costs were determined by volume, not weight. Interstate shippers were concerned more with shipping boards dry rather than wet, or rough, since shipping cost in those cases were based on weight.
Finally, in 1961, with subsequent revisions until 1963, the lumber standards we have today were pretty much set. The standards are in the table above.
From what I can tell there is one take-away message from this information. If you measure a 4x4 post and it measures to anything larger than 3 ½ in on a side then the post is likely older than 1961. The closer the post measures to it’s nominal size the older it probably is. Of course, as with everything historic, you can’t rely on one artifact to date your site and need to cross-date with other artifacts.
There. Now you know more than you ever wanted to know about dimensional lumber. You’re welcome.
See you in the field!!
(The reference is right below here where it says "reference")