Different Kinds of Metal Roof Trusses

Raised Heel Trusses

• A raised heel truss offers both structural stability and room for more insulation, which helps to increase a home's energy efficiency. The design raises and separates the top chord from the bottom chord to produce extra space at the eaves. The net effect is an added extension to the top of the exterior wall, allowing for the full depth of insulation to be applied in key areas above the ceiling.

Dropped Chord Trusses

• Dropped chord trusses are constructed with a secondary chord added below the bottom chord. The additional truss prevents the ceiling from gradually bending upwards, and provides extra space for full-depth insulation within the outer walls. The secondary chord also helps to create an airtight vapor barrier. Dropped chord trusses offer several technical advantages, but also suffer from financial disadvantages due to the added cost of installing taller studs, more blocking and more siding.

Scissor Roof Trusses

• Scissor trusses have their lower chords pointed upwards so that the lower chord resembles an arrow that is pointing upwards, with the tip of the arrow intersecting below the upper chord. The advantage of this design is that it allows space beneath the roof for constructing a cathedral ceiling. This design also helps eliminate the necessity of a load bearing wall in the center of the structure. The sloped ceiling coupled with the limited space can make it difficult to install insulation when working on this type of trusses.

Parallel Chord Trusses

• Parallel chord roof trusses, or flat trusses, are constructed with two chords running parallel to each other and supported by reinforcing trusses in between the top and bottom chords.The biggest advantage of this type of design is that it provides space for easy installation of generous amounts of insulation. Among the disadvantages of using this type of design are increased costs due to the additional steel braces and the difficulty of insulating the space between chords.

Attic Trusses

• Attic trusses are designed to provide an inexpensive way of creating additional storage space in a new home. Attic trusses resemble conventional "common trusses," but leave an empty space in the center to accommodate an extra room. Reinforcing trusses are placed on both sides, and above the room constructed in the center of the trusses. Attic trusses can provide more living or storage space, but will cost more to construct.

Bowstring Trusses

• Bowstring trusses, or Belfast trusses, are similar to conventional "common trusses" except for the top chord, which is constructed in a parabolic design. Bowstring trusses resemble the arched shape of an archery bow. The curved top chord and the horizontal bottom chord intersect each other at both ends. Bowstring trusses are designed to span large distances, such as those required for the roof of an aircraft hanger or warehouse.

Gambrel Trusses

• Gambrel trusses are constructed symmetrically with four slopes on the top chord. Two slopes are placed on each side with the lower slopes positioned at a steep angle and the upper slopes relatively flat. Gambrel trusses provide more room below the center of the trusses since the limited framing in the middle of the trusses increases floor space. Extra flat space for windows and skylights is also created by constructing the bottom chords at a steep angle.