Preservation ABCs is a series that will work its way from A to Z, bringing words into conversation that are relevant to historic preservation, whether it’s an idea, feature or vocabulary term. The idea is to help you see preservation everywhere you look and wherever you go. Enjoy! See previous letters.
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K is for King Post (Truss)
Pine Brook Bridge in Fayston, VT: A king post truss bridge. Source: Library of Congress. Click for source.
A king post is a type of truss, and can refer to building or bridge construction. Being able to identify a truss is an important part of preservation conversation, whether you are working on an architectural description or talking to a contractor or an engineer. As an introduction to trusses, start with an easy one: the king post truss. It is a simple truss and most often used for short spans. Think of it as a triangle. An easy definition of a king post is borrowed from Cyril Harris’ book, American Architecture: an Illustrated Glossary:
A structural support for a roof formed by two inclined rafters joined at the apex of their intersection. A horizontal tie beam connects the rafters their lower ends, and a vertical central member (called the king post) connects the apex with the midpoint of the tie beam.
See the triangle? This triangle is a truss and can repeat in bridges (then called multiple king post truss) and structures. They are easiest to identify on covered bridges or metal truss bridges or in attics. Take a look next time your passing over a bridge or hanging around an attic.
Got it? You can always jump to the HAER truss poster and dive right into studying.
Preservation in Pink 
Nice post on the Kingpost truss. There are several types of Kingpost trusses, but it depends on how they are used. In bridge terms, I know the one in the pic is close to the subdivided variant invented by J.A.L. Wadell, which I mentioned in a Mystery Bridge article enclosed below. Otherwise apart from the ones used for covered bridges, for steel truss bridges we have the normal one whose two top chords are supported by one vertical post. Those are rare to find and if so in clusters, including three known ones in Winneshiek County, Iowa. I shared your post in my Chronicles page and hopefully some others will contribute in terms of knowing where other King Post truss bridges can be found in the US and elsewhere! Well done!
Thank you Jason. I appreciate the additional king post lesson, and I’m sure readers do too.
Oh HAER poster, where have you been all my life?!
(nice post Kaitlin- sadly, this bridge is gone, right?)
Hi Josh. This bridge remains, I believe.
Glad you like the poster.
Likety like like! Thanks especially for the link to the HAER truss document.
thanks Jim! Great document, indeed.