Although today seen as nostalgic links to America's rural past, covered bridges were high technology for their time. Covered bridges used the timber construction familiar to Americans of the early 19th-century and in one sense, they were simply elaborations of the basic principle of the truss, which was the use of diagonal members to transfer vertical forces in a horizontal direction. What made them innovative was that they multiplied the basic truss pattern many times over. The patented truss systems employed in covered bridges allowed them to span a much greater distance than was possible with the timber-beam or king-post bridges of the Colonial era.
Covered bridges, at least in the beginning (the first covered bridge in America was built in 1805), were constructed not by local carpenters but by builders with special expertise in bridges. Isaac Damon of Northampton, Massachusetts, for example, built many of Connecticut's early wooden bridges. Improvements in truss design simplified covered-bridge construction. Ithiel Town's 1820 patented lattice truss had no complicated mortised joints and required no large timbers, only planks that were pegged together at the intersections. The truss patented by William Howe in 1840 used iron rods as tension members, leaving the timbers to bear only compressive forces. Connecticut today has examples of both these truss designs.
The roofs on covered bridges protected the trusses from rain and snow. Since the 18th century, simple trusses had been enclosed with planking, so adding a roof to protect the floor as well was simple common sense, especially since the roof structure added stability to the larger, longer trusses common in covered bridges.