Dendrochronology can identify the year in which a tree was cut. This identification of the year in which the tree was felled tells us that the roof timber must have been formed after the tree was cut. If, for example, timbers were felled in the year 1950, one can say that the structure in which the beams were used must have been completed after the year in which the timbers were felled.

Dr. Herman J. Heikkenen of the American Institute of Dendrochronology, Inc. conducted a dendrochronology study of the historic buildings at Stratford in 1986. To date the roof timbers, Dr. Heikkenen utilized a technique known as key year cross dating. This technique is based on samples of the annual growth rings taken from living or dead trees on a given site. Some years, such as those with extraordinary drought or rainfall, or incidence of fire, create tree rings of distinctive size or growth rate. Between these extraordinary years, there is a stable annual pattern of rings. By matching first the extraordinary rings, then the more normal pattern of rings, Dr. Heikkenen could place the roof timber sample in its proper chronological relationship to his other tree ring samples.

Dr. Heikkenen obtained his roof timber samples by taking a small plug of wood from a beam. At Stratford, Dr. Heikkenen limited his sampling to original roof timbers. The results of Dr. Heikkenen's research at Stratford established that the roof timbers of the construction of the Great House and out houses were hewed and sawed from yellow poplar and oak. The timbers for the Great House roof were felled after the growing seasons of 1737, 1738 and 1739.