Dating historic structures.(Design Notes)

As children, we were told that one could determine the age of a felled tree by counting the concentric rings on its stump. Later, we learned that this was poppycock. In fact, neither of these statements is entirely accurate. For quite some time, scientists have known that tree rings provide a permanent record of environmental changes during a tree's lifetime. Narrow rings are records of drought, while wide ones reflect steady moisture and light, and therefore periods of healthy growth. Master tree-ring chronologies, as they are known, gathered in a specific region, establish a basis for dating indigenous timber. This data can ultimately be an extremely accurate way to pinpoint the year of construction of timber-framed houses.

Three years ago the Society for the Preservation of New England Antiquities (SPNEA) in Boston was awarded a grant from the Massachusetts Historical Commission to establish a master treering chronology for white and red oaks in eastern Massachusetts. Additional funding from a number of sources enabled SPNEA to expand the study considerably to encompass the coastal region that lies between southern Maine and southern Rhode Island.

[ILLUSTRATION OMITTED]

Once completed, the chronology allowed scientists to determine the year, and even the season, that the timber used to frame a building had been cut, once they had taken a sample boring from framing timbers. The findings have caused SPNEA to revise the dates of construction for eight of its houses. These buildings had formerly been dated using conventional methods such as deeds, probate records, and other documents as well as by closely examining the construction techniques used. While the assigned dates for some structures remained in place, others were found to have been built years, and in two cases more than two decades, before or after the date determined by studying the documents. Because early builders generally used green wood, the framing timbers can be dated to within a year of when the tree was felled.

Several individuals were central to this undertaking: Anne Andrus Grady, a preservation consultant; Michael Lynch of SPNEA; Edward Cook and Paul Krusic at Lamont Doherty Earth Observatory of Columbia University in Palisades, New York; and Daniel H. Miles and Michael J. Worthington of the Oxford Dendrochronology Laboratory in Oxfordshire, England. Abbott Lowell Cummings, a former director of SPNEA and the author of the landmark volume The Framed Houses of Massachusetts Bay, published in 1979, was responsible for a preliminary study of this type carried out in 1975, and fittingly he has written an evaluation of the recent ...