A covered bridge is a timber-truss bridge with a roof, decking, and siding, which in most covered bridges create an almost complete enclosure. The purpose of the covering is to protect the wooden structural members from the weather. Uncovered wooden bridges typically have a lifespan of only 20 years because of the effects of rain and sun, but a covered bridge could last over 100 years. In the United States, only about 1 in 10 survived the 20th century. The relatively small number of surviving bridges is due to deliberate replacement, neglect, and the high cost of restoration.
Typically, covered bridges are structures with longitudinal timber-trusses which form the bridge's backbone. Some were built as railway bridges, using very heavy timbers and doubled up lattice work.
In Canada and the U.S., numerous timber covered bridges were built in the late 1700s to the late 1800s, reminiscent of earlier designs in Germany and Switzerland. They tend to be in isolated places, making them vulnerable to vandalism and arson.
The oldest surviving truss bridge in the world is the Kapellbrücke in Switzerland, first built in the 1300s. Modern-style timber truss bridges were pioneered in Switzerland in the mid-1700s.
Germany has 70 surviving historic wooden covered bridges.
The Holzbrücke Bad Säckingen spans the river Rhine from Bad Säckingen, Germany, to Stein, Switzerland. It was first built before 1272, and has been destroyed and rebuilt many times.
Switzerland has many timber covered bridges, including Kapellbrücke, Spreuer Bridge, and Neubrügg.
The Ponte Coperto in Pavia is a stone and brick arch bridge over the Ticino River in Pavia, Italy. The previous bridge, dating from 1354 (itself a replacement for a Roman construction), was heavily damaged by Allied action in 1945. A debate on whether to fix or replace the bridge ended when the bridge partially collapsed in 1947, requiring new construction, which began in 1949.
List of lists of covered bridgesMost bridges were built to cross streams, and the majority had just a single span.