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Why do people love the covered bridges?

“To begin with, they are pretty to look at and pretty to photograph,” says Benjamin D. Evans, a man who loves the covered bridges. “The fascinating thing about the old historic covered bridges is their craftsmanship. They are beautiful works of architecture.”

Evans should know. He and his wife and co-writer, June R. Evans, have photographed, documented, and written about hundreds of covered bridges in Pennsylvania and New England, including their 2004 publication, “New England’s Covered Bridges: A Complete Guide” (University Press of New England).

“The subject is immense,” Evans asserts. He isn’t kidding. Talk to a covered bridge enthusiast, and the data on history, design, preservation, restoration, and aesthetics just roll on and on. The National Society for the Preservation of Covered Bridges, founded in1950, publishes a World Guide to Covered Bridges, a quarterly magazine, and a newsletter. Covered bridges and their fans are found in almost every state. (Pennsylvania has the most; Vermont has about 100 bridges -- the greatest density in proportion to its size.)

When defining covered bridges Evans starts with the basics. By definition, a covered bridge must have two trusses (rigid frameworks), one on each side of the bridge. Trusses are the skeleton of the bridges. They come in many designs – often named after the engineer who created them -- and they are always based on a triangle shape because a triangle will not distort when it is placed under stress. A covered bridge must have a deck (floor) and a roof.

To be an “authentic,” a covered bridge must use one or more of the 21 specific trusses that are used throughout the United States. If a bridge looks like a covered bridge, but does not have trusses, receiving its support only from horizontal beams (stringers) anchored on opposite sides of a stream, it is called a “stringer” or a “romantic” bridge, not an authentic covered bridge. To be a “historic” bridge, it must be 50 years old or older. By definition, covered bridges do not have to be made entirely of wood, although all the country’s historic covered bridges are. Covered bridges may or may not have open sides or windows.

The principles of these bridges and their supporting systems had roots back in Europe, including a treatise from the 1400s by an Italian architect. American engineers working in the 19th century, Evans said, included “some people who used these theories and some who just figured out how to do it.”

Why were the bridges covered? A handful of myths attempt to answer the question, but the one and only answer is simple: to protect them from weather to better ensure their longevity. Here’s one weather-related disadvantage to covering the bridges: during the winter, bridges had to be “snowed.” That is, snow had to be carted into the bridge and spread over the dry deck to allow horse-drawn sleighs to pass through.