Covered Bridge Designs

Covered truss bridges are composed of a roadway, braced on each side by a wooden truss and a roof. The purpose of the siding and roofing was to shield the trusswork from the weather to ensure a longer lifetime, not to protect travelers from the weather. (Frugal Yankees would not waste money and effort on such frills.)

The truss designs are masterpieces of engineering, each one designed to exploit the best properties of wood and avoid the bad qualities. Ithiel Town, a Connecticut engineer, developed the Town lattice truss in the early 1830's. Theodore Burr, another New England engineer, produced the Burr truss in the same period. The Long truss was patented in 1830 by a Hopkinton, New Hampshire native, Col. Stephen H. Long. This was said to be the first wooden truss in America into which "a few mathematical calculations entered".

Some of these truss designs were first used in railroad bridges. Local bridge builders then copied them. In some cases, the original designers contracted to build the spans. Many local New Hampshire carpenters also built bridges: James Tasker, for example. The Dingleton, Blacksmith Shop, Cornish-Windsor, Blow-Me-Down, and Meriden bridges are examples of his work.

As loads became heavier, the laminated arch was added for strength. Sometimes repairs had to be made, and the latter-day engineers did not follow the original truss designs. As a result, one is apt to find bridges which do not fall exactly into the more common types of truss design.

The earliest bridges were built by farmers, who, using the same methods they used to build barns and churches, erected spans based on the earliest designs they had--the King and Queen posts, gradually improving them as they went along. The simple King post proved unsuitable for major spans, but many Queen post bridges were built, although very few are left today.

The size of the opening of the bridge was usually based on the height and width of a load of hay. Walkways were usually provided on bridges in towns. All depended upon the local requirements. It is very rare to find two bridges exactly alike, for no two situations were alike. Early bridges used different forms of wooden trusses only; later spans used iron fittings in addition to wood. There were many variations from the standard truss designs, and embellishments were sometimes added to the facades and eaves.

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