The Gambrel Truss is another design more common to America than Europe, although it has been historically used in Britain. However, this is complemented by a pair of diagonal beams enclosing these steps for an exceptionally rigid and strong frame. This style foregoes a tie beam or collar completely, using a set of small beams and posts in a stepped structure similar to a Hammerbeam Truss. For a design such as an open ceiling in a living room this provides all the necessary strength with a more novel design. The space above can incorporate various combinations of posts and braces, to give styles such as the Howe Scissors or Modified Queen scissors. In some variants, these beams meet in the middle but do not extend all the way to the rafters. The basic Scissor Truss design is named after its resemblance to an open pair of scissors, with two crossed diagonal beams and a small king post. These beams prevent spreading of the rafters in a similar way to a Hammerbeam Truss. This forms a design somewhere between a Collar Truss and a Scissor Truss, sometimes known as a Raised Tie Scissor. An inverted version is sometimes used as a particularly strong Mono Truss to support a one sided roof structure.Ĭoffer Trusses are a variation on a Raised Tie beam truss, incorporating two diagonal beams from the rafter bases to the collar. Other members can be added for a more complex, decorative effect. More usually, two more braces are added to form a ‘W’ shape within the truss. The rarest and simplest design consists of a Tie Beam and rafters with two diagonal braces from the apex to the beam. The Fink Truss design is more common in America and relatively uncommon in British Oak Framed buildings. For particularly low ceilinged rooms, an exposed ceiling and Collar Truss can increase the height and lighting significantly. As a normal tie beam prevents spreading of the rafters at the base, the mortis shoulders at the base must be strengthened.Īlternatively, two short beams and posts can be added to the base of the rafters to form a Hammerbeam Truss ( The roof of Westminster Hall is a great example of a hammerbeam roof). This is the ‘raised tie beam’ that gives the truss its name and is surmounted by a shorter King Post and diagonal braces. Instead a shorter beam, known as a Collar, is situated further up the rafters. The square space in the middle acts as a tunnel from one end to the other.Ĭollar Trusses lack the traditional long tie beam connecting the base of the upper chord rafters. Queen Post Trusses are particularly useful for attic spaces where access to the whole length is required. The addition of a top post and diagonal braces reinforces the truss and enhances the design. Overall strength increases with a collar beam connecting the tops by incorporating another triangle into the shape. Queen Post Trusses replace the King Post with two smaller posts from the tie beam to the slopes of the rafters. Often this will incorporate two straight or curved diagonal braces.Īdditional posts and braces can be added symmetrically to create designs such as the Howe and Double Howe. This is completed by a king post connecting the apex of the triangle and the centre of the beam. The most basic form consists of two rafters and a beam connected by pegged tenon and mortice joints. King Post Trussīy far the most common British style, King Post Trusses are the most recognisable roof truss design. However, the ways in which these are combined can lead to some amazing and inventive results. Even the most complex roof trusses are formed from a series of interconnected triangles. All oak roof truss designs derive their strength from the inherent rigidity of triangular structures. While oak already benefits from an attractive texture and soft, warm colouration, a feature truss made of oak enhances an exposed ceiling. For oak timber structures with an open ceiling design, decorative roof trusses are an eye catching and elegant finishing touch.
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