Bridge Description Bath Covered Bridge, Bath New Hampshire
The abutments and two original center piers of Bath Bridge are of dry-laid stone, but their orientation is odd. The two abutments are more or less square to the river, but the two piers are both skewed. This makes the span lengths different from one side of the bridge to the other and presented obvious challenges in framing the trusses. Moreover, the original span lengths were very uneven; the two piers are spaced closely together in the middle of the river. There is no obvious explanation for this peculiarity. Perhaps subsurface conditions for foundations dictated the placement of the piers, or there may have been some special problems regarding the flow of the river's current.
The total truss length of Bath Bridge measures 374'-5 3/4" at the floor. Structure length of the east span is 127'-2 1/4" on the upstream side. The downstream side was not measured, but is two panels longer because of the skewed pier. From the position of the truss center posts in relation to the highest point of the arch, it is evident that the builder intended the upstream truss to be the standard and the downstream truss to be the deviation. The center span is only 71'-10" in structure length, while the long original west span was 175'-5 1/2". Here the downstream truss measures three panels shorter, so this pier appears to be more skewed than the other. Where the short center span meets the long original west span, the builder had trouble fitting his panel lengths to the piers, so there is an odd short panel.
Posts and braces show manufacturing variation, but on average measure 4-1/2" x 5-3/4". The braces do not foot on shoulders on the posts in the same plane. Instead, they are treenailed across the outside of the post frame with a single 1-3/4" treenail at the joint and no mortise. They overlap the panel points and continue on to the chords, where they are mortised through. The chords themselves are built up of three vertical leaves, with posts mortised through the inside joint and braces mortised through the other. This framing detail is surprisingly similar to the counterbrace treatment developed a decade later by Peter Paddleford of nearby Littleton, but there is no evidence connecting him with Bath Bridge.
Bath Bridge also has original timber arches integral with the trusses. Like the chords, they are built up of three vertical leaves of timber placed together with no space; the posts are mortised through the inside joint, and the braces are mortised through the outside joint. The arch ends are tied to the lower chords and do not foot directly on the abutments. Such intricate joinery requires an almost unthinkable amount of custom labor.
Bath Bridge represents the early, idiosyncratic craftsman tradition of wooden truss bridge building, before designs became more standardized under the influence of the major patented truss plans. It is very difficult to classify. It is more like a Burr truss than anything else, but the standard Burr does not have the braces overlapping the panel points, and it usually has the arch footing directly on the abutments. Because of the overlapping braces, Bath Bridge slightly resembles the Haupt truss, but this was not patented until 1839, and the 1832 date for Bath Bridge is very well established.
One other New England covered bridge shares the same truss plan, the Sayres Bridge over Ompompanoosuc River at Thetford Center, Vermont. The framing details are rather similar, but the timber sizes are different, and the brace/post joints are made with two treenails, not one as at Bath. These two bridges may be the last remnants of an old regional building tradition, but neither date nor builder are known for Sayres Bridge. It is often inaccurately listed as a Haupt truss.
Bath Bridge is unusually wide inside, measuring 22'. Of this, about 18' is the roadway, and about 4' is a separate raised sidewalk platform along the upstream side. It is impossible to tell whether the bridge had this feature as originally built.
The floor beams measure about 7-1/2" x 15-1/2" but are not original. There are two per panel, and as the panel spacing is only about 4', the floor beams are numerous.
Like other New Hampshire covered bridges, Bath Bridge has been modified over the years, especially during the early twentieth century.