Maximizing Value: 5 Key Factors in Light-Gauge Steel Truss Costs

Maximizing Value: 5 Key Factors in Light-Gauge Steel Truss Costs

There are several factors that contribute to the cost of light-gauge steel trusses. When planning out a project to be structurally sound and economically competitive, these are all important details to take into consideration. Considering these factors and working closely with a structural engineer or our truss draftsman can help determine the most cost-effective solution for your project.

First, it is important to define what light-gauge steel trusses are and how they are used. They are structural, webbed members used to support floors or roofs that are made from galvanized steel between the gauge sizes of 12 and 24. The webs are the angled members that connect the top and bottom chord of the truss together. The magnitude of the tensile or compressive stresses applied determine what gauge and depth to design each truss piece out of. Thicker gauge pieces are stronger, but they weigh more, so the configurations of member sizing need to be optimized to reduce weight and maximize strength. This is done using our light-gauge steel truss engineering design software. The size and shape of these members make them ideal to be a simpler, more recyclable, and more efficient replacement to wooden trusses that are traditionally used to frame roofs and floors.

Design Loads for Light-Gauge Steel Trusses

When designing trusses, we need to account for various loads such as wind, snow, rain, live loads (e.g., people, furniture), and dead loads (e.g., the weight of the roofing material). Higher loads may require stronger and more intricate truss designs, which can increase costs. Rain and snow loads can be directly minimized by increasing the slope of the roof, so precipitation slides off quicker and doesn’t accumulate as much. The type of roofing and building code both determine the dead and live loads to be accounted for. Accurate wind and snow loads are found in ASCE tables that are determined by location and building type. Areas on the Gulf coast, like Louisiana and Florida usually have to account for higher hurricane-level wind speeds, potentially increasing the price of a truss system. Also, areas with heavy annual snowfall, like Pennsylvania or Colorado require stronger trusses to support additional loads. Since the design loads are often quantified as a pressure, in pounds per square foot, the spacing between light-gauge steel trusses is very important in determining the amount of weight (in pounds) that they will need to hold. Typical spacing is 24 inches on center (O.C.) or occasionally 48 inches O.C. The larger the spacing is, the more weight is applied and the stronger the trusses have to be.

Roof Geometry: How complex is your roof framing?

The shape and complexity of the roof affect the design and fabrication of trusses. Simple, standard roof designs are generally more cost-effective than complex or custom designs that require additional engineering. Also, incorporating special features or customizations, such as skylights, dormers, or architectural details, can add complexity and cost to the truss system. Below is an example of some light-gauge steel trusses with a vaulted ceiling that splits the bottom chord.

Roof trusses in a a house that have a vaulted ceiling in one room that splits the bottom chord of the light-gauge steel trusses.

There are three main types of roofs, going from simplest to most complex: mono-slope, gable, and hip end. A mono-slope roof has only one constant slope across the truss. A gable roof has two, usually identical slopes, that meet up at the middle of the span, and they only require one type of truss across the length of the roof. Usually, if siding is going on the ends, a gable end truss is used, which has vertical webs that act as studs lining up with the wall panel studs. A hip end roof has an additional slope on the end of a gable, and it requires additional engineering to properly support the edge. A girder truss, setback from the end by typically 6 feet, holds the weight of many perpendicular jack trusses, as shown in the image below.

Hip-end roof framing in a 3-D layout modeling program that is used to design light-gauge steel trusses.

Mono-slopes and gable ends are both straight-forward and simple truss systems, while hip-ends are more complex and demand more material usage, causing them to be more expensive usually. Though they might look like they don’t make up “as much roof” as a gable, they require more, different truss types and shapes, which increase labor costs and complicate the material list.

Optimal Sizing for Trusses: Roof Height, Heel Height, Depth of Trusses

Typically, light-gauge steel trusses with a greater slope will be stronger than trusses with a smaller slope and flat trusses of the same span. This is because more material is being used to brace the middle of the span which deflects the most. A steep-sloped truss redistributes loads more efficiently. Weights acting on the middle of the roof, such as snow accumulation or wind pressure, are more directly transferred to the supporting structure (e.g., walls or columns) rather than being solely borne by the truss itself. This reduces the amount of stress experienced by truss webs, enhancing overall strength. Below is an example of some weak-axis floor trusses for a home in Pennsylvania.

Weak-axis light-gauge steel trusses being used to frame the floor of a home in Pennsylvania.

The heel height, distance from the top of the bearing wall to the top chord directly above it, typically is about 12 inches high. However, if necessary, the heel height can be increased to add strength to a truss. This is particularly useful when trying to strengthen floor or flat trusses. For one particular job, the customer wanted a vaulted ceiling, which tends to weaken the truss by splitting the bottom chord. Instead of using the typical heel height of 12 inches, we bumped it to 16 inches, allowing for greater depth within the webs and making the truss more stable. 

Supports and Bearings: What is holding up your roof’s framing?

The method of supporting the trusses, such as using load-bearing walls or columns, affects the design and cost as well. The width of the support also needs to be taken into account when designing proper fastening systems, such as brackets or ties. Trusses need at least two bearing points to be structurally sound, ideally one on each end. Additional supports are ideal for longer spans or heavier loads. Typically, the maximum span for light-gauge steel trusses is between 30 and 40 feet depending on the local building code or standards. Any longer than that, and it becomes inefficient or impractical to use this kind of framing.

Light-Gauge Steel trusses and studs being used to frame a small hip roof at the front of a Spark by Hilton hotel.

Here is an image from the structural plans of a project with a span of 70 feet from outer wall to outer wall, which is too long to practically use light-gauge steel trusses for. Instead, the span was split up across the two central, load-bearing hallway walls into two 30-foot spans and one 10-foot span. Splitting up the span allows the truss to be broken up into three pieces, which not only reduces the structural strain on the truss members, but also greatly increases the ease of transportation by putting the truss length below the standard truck bed length of 53 feet.

Structural top-view drawing of a project with a long span of 70 feet being split up by two central hallway walls so that light-gauge steel trusses can be effectively used.

Framing Assembly: Pre-Assembled vs. Assembled-on-Site Trusses

One benefit of a light-gauge steel truss system is that their assembly is very straightforward, as all pieces come pre-cut to exact lengths already, eliminating on-site waste. We can either pre-assemble trusses to be delivered intact to the jobsite, or send the pieces and plans so that they can be constructed there. Pre-assembly adds to the labor cost, and potentially makes delivery less efficient, because stacked pieces are easier to load and make room for on a delivery truck than pre-assembled trusses. For smaller jobs, however, pre-assembly is often a simpler and more cost-effective option that reduces on-site labor.

Light-gauge steel trusses being pre-assembled by employees at US Frame Factory in New Iberia, Louisiana.

Additional Resources

Framing Clips and Accessories

Buy Metal Studs Online | Ship to Houston, New Orleans (usframefactory.com)

Slotted Deflection Track: Application and Installation (usframefactory.com)

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