Collar beam

thumb|Roof framing: element #5 are the collars thumb|An old collar beam roof in the Netherlands. Image: Cultural Heritage Agency of the Netherlands

A '''collar beam''' or '''collar'''<ref>Ensminger, Robert F.. ''The Pennsylvania barn: its origin, evolution, and distribution in North America''. Baltimore: Johns Hopkins University Press, 1992. 324. Print.</ref> is a horizontal member between two rafters and is very common in domestic roof construction. Often a collar is structural but they may be used simply to frame a ceiling. A collar beam is often called a '''collar tie''' but this is rarely correct. A tie in building construction is an element in tension rather than compression and most collar beams are designed to work in compression to keep the rafters from sagging.<ref>Maginnis, Owen B.. ''Roof framing made easy: a practical and easily comprehended system, adapted to modern construction, for laying out and framing roofs, adapted to modern construction'' .... New York: O.B. Maginnis, 1896. 7. Print.</ref><ref>Nicholson, Peter. ''Practical carpentry, joinery, and cabinet-making; being a new and complete system of lines, for the use of workmen: founded on accurate geometrical and mechanical principles, with their application in carpentry, to roofs, domes, centring, &c.; in joinery'',. London: T. Kelly by J. Rider, 1826. 31. Print.</ref> A collar near the bottom of the rafters may replace a tie beam and be designed to keep the rafters from spreading, thus are in tension: these are correctly called a collar tie.

==Etymology== ''Collar'' in general comes from Latin ''collare'' meaning neck. <ref>Oxford English Dictionary Second Edition on CD-ROM (v. 4.0) Oxford University Press 2009</ref>

==Collar beam roofs== The simplest form of roof framing is a common rafter roof. This roof framing has nothing but rafters and a tie beam at the bottoms of the rafters. The next step in the development of roof framing was to add a collar, called a collar beam roof. Collar beam roofs are suitable for spans up to around (4.5 meters).<ref>Moncrieff, G. K.. ''The principles of structural design'',. Chatham, Eng.: W. & J. Mackay & Co. [for] the Royal Engineers Institute, 1897-98. Print.</ref>

==Crown post roof framing== A crown post is a compression member, a post, in roof framing which carries a longitudinal beam called a crown plate. The crown plate in turn carries collar beams which help support and carry the rafters, thus collar beams are always found in crown post roof framing.

==Arched brace roof== The arch brace truss is made by adding two braces between the rafters and collar. This puts the collar and the braces in tension.

==References== {{Reflist}}

Category:Roofs