There are a seemingly countless number of types of roof truss styles. In fact, since custom roof trusses can be made according to a particular homeowner's needs or wishes, the possibilities really are countless. Most homes, however, typically employ one of four major types of roof truss design: raised heel, dropped chord, scissor, and parallel. Each of these types offer distinct advantages and disadvantages, depending on the application.
A raised heel roof truss separates, or raises, the top chords, or top edges of the truss, from the bottom chord. This results in extra space at the eaves which in turn, provides enough space for full depth insulation in key areas above the ceiling. This is especially helpful for homes that are more likely to experience ice damning. This design also helps to create an airtight vapor barrier that reduces the likelihood of condensation forming, helping to eliminate dry rot and mold. Drawbacks to this style are mostly financial due to the requirement of more materials necessary to complete the overall, final structure.
Dropped chord trusses provide a secondary chord below the bottom chord. This type of roof truss design helps to reduce lift and provides extra space for full depth insulation within the outer walls. It also creates a positive airtight vapor barrier. Drawbacks to this type of roof truss design are also mostly financial. The use of taller studs, more blocking and more siding increases construction costs.
In a scissor roof truss, the bottom chord is made of two pieces that are not parallel to the ground. Instead, the bottom chord is set at an angles, similar to the top chord. The sloped nature of the bottom chord allow for the interior of the home to have a vaulted or cathedral ceiling. When used in conjunction with a raised heel design, a full depth of insulation is also possible. This design also helps eliminate the necessity of a load bearing wall in the middle of the structure. The major drawback to a scissor truss is that the design allows for limited access to install insulation.
Parallel chord roof trusses, also known as flat trusses, utilize two chords running parallel to eachother. Like all roof trusses, these top and bottom chords are joined by the interconnecting web of materials. Steel and other metal materials are often used to help reinforce the structure, especially at the joints, or nodes. The major advantage of the parallel chord roof truss design is that it provides space for easy installation of large amounts of insulation. Drawbacks include increased costs due to the requisite steel braces, as well as the additional challenge of insulating the additional space between chords.
Under each of these four main categories, there are numerous styles that are designed to fit individual situations. Distinguishing factors between the types are the number of boards used for the web, and the distance the bottom span can reach. Types include: king post, queen post, fink, howe, fan, modified queen post, double fink, double howe, hip, scissors, monopitch, cambered, dual pitch, gambrel, polynesian, attic, bowstring, stub, inverted, piggyback, studio, cathedral, sloping flat, and flat. While ready-made trusses typically fall into one of these standard types of trusses, custom roof trusses can also be created to suit one's particular needs.