Barns are perfect for studying construction techniques. Unlike in a house, in a barn the structure is out in the open. It’s not hidden behind walls or ceilings or insulation. It’s not tucked away in the attic or basement. Everywhere you turn you can see clues to the way in which the building was constructed.
While there are many things that can be examined to understand the way in which a barn was built – e.g. the way in which the timbers were shaped, the types of nails used to join pieces of the frame together, the way in which the roof is constructed, or even the placement of specific timbers within a frame – this essay focuses on one aspect of construction: the way in which timber frames for barns were laid out and constructed.
Timber framing can be accomplished in two basic ways, called scribe rule framing and square rule framing. The difference between the two is the way in which the timbers are prepared for joining.
In scribe rule framing, each connection between timbers is unique. The carpenter laying out joints in the frame used a pair of dividers and a marking device to transfer the irregularities of one timber to its mate. (This process, known as scribing, gives the technique its name.) This ensured a tight joint, but required that the frame be assembled in exactly the way that it had been laid out, since joining two parts that hadn’t been scribed to match each other would lead to an imperfect joint. For example, the corner posts are not interchangeable, even thought they performed the same function.
Square rule framing, on the other hand, relies on greater uniformity. Rather than cutting joints so that one timber matches another, the timbers are formed to match a uniform standard at the joint. This meant that timbers that performed the same function in a building became interchangeable. For example, all the ends of the posts might be made into 8x8 inch timbers. For the purpose of joining timbers, the pieces were identical. Since the only portions of the timbers that mattered from this point of view were the areas of intersection, only these parts were made regular. The rest of the timber’s length could be left irregular.
Each of these techniques leaves distinctive traces on a frame. Scribe ruled frames are characterized by an elaborate system of marriage marks or raising numerals. (Figure 1) These guarantee that the two timbers that have been scribed to match perfectly are joined together. Similarly, square rule buildings are characterized by a distinctive shaping of the timbers. Since the crucial area of the timber is around the joints, the irregularities of the wood are cut away close to the point that timbers intersect. (Figure 2) It’s a bit like taking a log and making it into a two-by-four at each joint.
Square rule framing is tantalizing to anyone who wants to nail down the date of construction for a building, especially barns since these tend not to appear as frequently in documents and records as other building types. It offers the hope of what archeologists call a terminus post quem (a “date after which) for barns built using the technique. It suggests the possibility of a watershed moment, dividing timber frames into two distinct camps. But the technique has only recently come to the attention of architectural historian, and we are still trying to pin down its date of introduction. It first appeared in print in Edward Shaw’s Civil Architecture, the first edition of which was published in Boston in 1831 by Marsh, Capen and Lyon. While this may provide the date for the first time that the technique was described for a national audience, it was clearly known in Connecticut before 1831. The Connecticut Trust Barns Survey turned up what is currently the earliest well-documented example of a barn with a square rule frame close to home. Literally. The Eli Whitney barn, well-documented to have been constructed in 1816, sits next to the Trust headquarters in Hamden and is the earliest example of a square rule building discovered to date in Connecticut. (Figure 3) Documentary evidence suggests that the technique may have been used even a bit earlier, as a January 1814 advertisement in the American Mercury for Samuel Blin, Jr.’s School of Architecture in Wethersfield includes the “square rule of framing” as part of the curriculum. (Figure 4)
Refining our understanding of square rule framing requires far more than just identifying the date that it was introduced. In the future, we hope to understand when, and how, the technique spread throughout the state. Were Wethersfield and the Blin family of joiners the starting points for square rule framing, or did it appear elsewhere in the state (or region, or country) and spread to Wethersfield via the Connecticut River? Another question raised by the technique concerns how quickly it was adopted. The Bates-Scofield Barn, in Darien, contained an interesting mix of the two techniques – clear raising numerals combined with text book square rule shaping of the timbers. (Figure 5) With the help of dendrochronology (tree ring dating of the timbers) we know the building was constructed around 1827. Further research will have to determine whether this signals the beginning of square rule framing in this part of the state, or if the builder of this particular barn continued old habits after many in the area had adopted the new technique.