Queen Post Truss

A queen post truss is a timber roof frame in which two vertical posts, the queen posts, stand on the tie beam at equal distances either side of the centre. Their tops are joined by a horizontal straining beam (or collar), and the sloping principal rafters run from the wall plates past the heads of the posts toward the apex. The arrangement leaves an open rectangular space in the middle of the truss.

How it differs from a king post truss

A king post truss has one central post; the queen post version replaces it with two. The posts typically support purlins, and the straining beam keeps the post heads apart. Because the middle section relies partly on bending in the horizontal member, the basic queen post truss is generally suited to modest spans, though historic builders used it for larger roofs than a simple king post could cover.

The open centre made queen post roofs useful where attic space or headroom was wanted, and the form appears widely in British and North American timber buildings, barns and churches.

Historic terminology

In British historic building records, a queen post is described as working like a crown post but set in pairs, spaced equally away from the centre. Heritage thesauri record "queen post truss" as a distinct roof type for classification of historic buildings.

Modern use

Queen post forms survive in modern timber framing, exposed trusses in great rooms and porches, and some prefabricated trusses. Like all trusses, they should not have members cut or removed without engineering advice.