Slope/Pitch

Pitch is one of the most common characteristics of roof trusses and is required to determine the geometry of the roof. It can describe the roof pitch, or the angle of the top chord, as well as the pitch of a vault or the angle of the bottom chord in cathedral ceiling applications. Industry norm is to standardize all pitch values to a common denominator, 12 inches, or how much the roof rises over one foot. For example, a 5/12 pitch is 5 inches of rise over 12 inches of run and is simply described as saying the two numbers “five twelve.” Other regional variations for stating the pitch include “five over twelve” and “five and twelve.” Values can vary from 0/12 pitch for a flat truss to 24/12 for a very steeply pitched roof. Common values include 4/12 to 12/12 pitch roofs and can also include fractions (6.5/12) in the pitch to achieve a specific truss height for a given span.

The greater the pitch, the more area the truss technician has to work with to apply triangulation and the more efficient the webbing can be. However, increases in pitch directly affect top chord length. Pitch, combined with span and heel height, determine the overall height of the truss. Truss height has limitations in production and shipping and should be taken into account during the design phase of a project. Steps can be taken to work around these limitations but it’s best to know about them upfront to make proper accommodations.

In scissors or cathedral trusses where a vault is desired, the ceiling pitch is typically half the roof pitch. For example, a roof pitch of 8/12 can easily accommodate a 4/12 vault for most design considerations. Instances where a ceiling pitch greater than half the roof pitch is desired can be accommodated but are subject to other design specifications such as span, loading, building codes, and other engineering factors. Increasing the heel height can aid in designing these types of trusses, giving the truss additional space to incorporate webs and ultimately transfer loads. Parallel chord trusses have the same roof pitch as ceiling pitch and are able to accommodate this through a raised heel.

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