In the US you often see covered bridges, why are they covered?

Answer

Dear Steve,

This is almost always about 19th century or early 20th century wooden half-timbered bridges. If you don’t protect them against the weather, the structural elements rot quite quickly (sometimes even after 10 years, depending on the wood species). Putting a roof over it protects the structural wooden part of the bridge and makes it last much longer (many still exist today and are up to 150 years old). It is important to maintain the wooden roof.

regards

dr. ir. Robrecht Keersmaekers