Kinds of Steel Roof Trusses

Common Truss

• The common steel truss is the one used most in roof construction due to its simplicity, effectiveness and low production cost. This truss is recognized by its triangular shape, created by a bottom chord that acts as a base while two top chords form a pitch where the roof sheathing is applied. A king post and two truss web posts in the center of the triangle create additional support, with each joint held together by a metal gusset. The size of the chords and configuration of the truss itself are usually determined by the span and weight of the structure's roof.

Parallel Chord Truss

• A parallel chord truss, sometimes called a flat truss, features two steel chords that run parallel to each other, while alternating vertical and angled web posts connected to the chords by gussets provide support in between them. While parallel chord trusses are more commonly found in floor construction, they are sometimes used on roofs of large commercial structures such as warehouses and stages. In certain instances, they are used at the base of cathedral ceilings, because they allow easier and fuller insulation of the attic area.

Raised Heel Truss

• Raised heel trusses are sometimes referred to as energy trusses because they are more energy-efficient than structures with shallow heels. The heel is the corner of the truss that sits on the outside wall of the home, and it is measured vertically from the top of the wall to the bottom of the roof sheathing. Raising it from the standard 4 inches to 10 inches or more allows for needed airflow from soffit vents and full attic insulation all the way to the wall. However, these trusses are generally more expensive to manufacture.

Dropped Chord Truss

• Dropped chord trusses are designed to create a vapor barrier that protects against mold and dry rot while also allowing for full attic insulation, just like raised heel trusses. A standard dropped chord truss consists of a conventional truss with a secondary chord suspended beneath it to reduce wall damage caused by ceiling uplift. Building costs are typically greater with this type of truss because additional siding and taller studs are required to create the required vapor barrier. However, long-term maintenance and repair costs are often lower as a result.

Scissor Truss

• The scissor truss is shaped much like a boomerang or hand-glider, with two top chords and two lower chords all bowed inward, while a king post anchors the center. It is similar to a common truss, except that two sloping lower chords replace the one bottom horizontal chord. Scissor trusses became fashionable due to their aesthetic appeal and are often used to create cathedral ceilings. Although they remove the need to install a bearing beam for support, they also make insulating the attic area much more challenging.