What is a Covered Bridge?

There are 17 historic wooden covered bridges in the U.S. state of West Virginia. Only three of these bridges were built before 1870 and they are the three longest in the state. Each uses a standard truss design, braced with the Burr Arch.

What is a Covered Bridge

A covered bridge is a timber-truss bridge with a roof and siding which, in most covered bridges, create an almost complete enclosure. 

Why is it covered?

The purpose of the covering is to protect the wooden structural members from the weather. Uncovered wooden bridges have a life span of only 10 to 15 years because of the effects of rain and sun.
Bridges having covers for reasons other than protecting wood trusses, such as for protecting pedestrians and keeping horses from shying away from water, are also sometimes called covered bridges.

History


Early timber covered bridges consisted of horizontal beams laid on top of piles driven into the riverbed. The problem is that the length between spans is limited by the maximum length of each beam. The development of the timber truss allowed bridges to span greater distances than those with beam-only structures or arch structures, whether of stone, masonry, or timber.  In the mid-1800s, the development of cheaper wrought iron  and cast iron  led to metal rather than timber trusses, except in those areas of plentiful large timber.

Today

According to Covered Bridges Today  by Brenda Krekler, as many as 12,000 covered bridges once existed in the United States; that number dropped to under 1,500 by the 1950s.  The National Society for the Preservation of Covered Bridges was formed in 1950.

See Some Examples