A collar beam or collarEnsminger, Robert F.. The Pennsylvania barn: its origin, evolution, and distribution in North America. Baltimore: Johns Hopkins University Press, 1992. 324. Print. is a horizontal structural member placed between two rafters to resist compression. Common in domestic roof construction to prevent rafter sag, a collar beam is often colloquially called a collar tie, but is unlikely to be one unless placed high or low on the rafter, as a tie in building construction is an element in tension rather than compression.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.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. A collar placed near the top of the rafter is in tension, as is one placed below its midpoint towards the bottom. Each would keep the rafters from spreading, and be correctly called a collar tie. A collar beam may also double as a ceiling joist, providing a member for attaching drywall or other material while also serving to resist rafter sag.Framing a Raised Ceiling, Ceiling Joists, mycarpentry.com
Etymology Collar in general comes from Latin collare meaning neck. Oxford English Dictionary Second Edition on CD-ROM (v. 4.0) Oxford University Press 2009
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).Moncrieff, G. K.. The principles of structural design,. Chatham, Eng.: W. & J. Mackay & Co. [for] the Royal Engineers Institute, 1897-98. Print.
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.
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