I Joists vs Floor Trusses - Making the Best Choice for Your Build
When designing the floor framing system for a residential or commercial building project, two of the most common options are I-joists and floor trusses. Both can provide the structural support needed, but they have some key differences that impact their performance, cost, and ease of installation.
Structural Performance
The primary purpose of any floor framing system is to safely support the expected loads in a building. This includes not only vertical loads from people, furniture, and storage, but also lateral loads from wind and seismic forces.

Load-Bearing Capabilities
I-joists can be designed and engineered to meet required load-bearing capacities for residential and some commercial buildings. Their performance is a factor of the type of laminated veneer lumber or oriented strand board used in fabrication, as well as the adhesives bonding these engineered wood products together.
Floor trusses provide very high structural strength, as the triangulated structure evenly distributes forces throughout the entire system. Property engineered trusses can accommodate extremely heavy vertical and horizontal loads, making them well-suited for larger commercial buildings.
Span Capabilities
The span capability compares the maximum distance floor systems can cross between structural supports or walls. Longer span capabilities reduce costs by requiring less intermediate supports.
Standard I-joist designs allow spans of up to 20 feet for residential applications. The most common floor truss designs facilitate spans over 30 feet, with custom trusses engineered for exceptional spans exceeding 50 feet in commercial buildings.
Resistance to Deformation
Excessive bending, sagging, twisting, or deformation under load can compromise structural integrity and performance. I-joists are highly resistant to bowing or deformation thanks to the laminated structure and stiffness of the engineered wood and adhesives.
Floor trusses also demonstrate minimal deformation under heavy vertical or horizontal loads. The triangle shapes provide excellent resistance to diagonal twisting forces.
Customization
The ability to easily customize floor systems to accommodate design changes or updates is also an important consideration. I-joists can be cut, notched, or altered at a job site with standard carpentry tools. This facilitates flexibility and modifications during construction.
However, floor trusses have very little tolerance for field modifications, as even minor changes can severely impact structural soundness. Adjustments require consulting the truss engineering firm to re-evaluate and recertify the design.
Cost Differences
When evaluating floor framing options, the costs of materials and installation are common deciding factors for any builder or construction manager.
Material Costs
On a per linear foot basis, engineered wood I-joists typically have a lower cost compared to assembled metal-plate-connected floor trusses.
However, trusses offer significantly lower costs per square foot. This is because truss designs allow for wider spacing between structural members thanks to their exceptional rigidity and span capabilities.
Installation Costs
The lightweight design of I-joists enables faster installation compared to bulkier floor trusses, reducing overall construction schedules. Framing crews can lift and fix I-joists using minimal equipment and effort.
Setting floor trusses often requires heavier lifting gear like cranes or forklifts, adding rental costs. The complexity of properly aligning and connecting trusses also increases labor hours, and potentially necessitates trades specialists to supervise the process.
Construction Considerations
While meeting structural and budgetary demands are central factors, the constructability and integration of any floor framing system also warrants deliberation.
Ease of Installation
I-joist installation is comparable to traditional sawn lumber joists, enabling framing crews to quickly incorporate them using well-honed techniques. The lightweight engineered wood and standard depths simplify material handling and connections.
Installing metal-plate-connected floor trusses requires more meticulous planning and coordination. The heavy components can also congest job sites with lifting equipment and trades personnel during the assembly process.
Integration with Other Systems
Floor framing must accommodate openings and clearances for ductwork, piping, wiring, and other environmental systems. I-joists can be easily notched or drilled on-site to provide necessary openings after coordination with trades.
Because floor trusses cannot be cut or altered without extraneous engineering analysis, all openings and services must be pre-planned and integrated into the original truss designs. This demands extra design coordination for successful system integration.
Fire Safety
Controlling fire spread and structural survivability during a fire emergency are critical functions for any building. I-joists fabricated with fire-retardant lumber or large cross-sections demonstrate good fire resistance for one-hour or two-hour ratings.
Floor trusses inherently provide exceptional passive fire resistance thanks to the insulating layers of air space between the triangular chords. Large wood trusses easily achieve one-hour or two-hour fire ratings for residential and commercial compliance.
Noise Reduction
Excess noise transfer between occupied floors can create comfort issues and privacy concerns in mixed-use buildings. While lightweight I-joists allow mid-construction modifications like sound insulation inserts, the thin profile limits space for absorptive batt insulation.
Conversely, floor trusses can be easily designed with wider cavities and chord spacings to incorporate noise dampening insulation. This facilitates noticeably quieter inter-floor noise levels using cost-effective insulation and wall assemblies.
Sustainability Impacts
Sustainable construction practices are vital for environmental stewardship. I-joists utilize engineered wood materials that optimize forest resources by using smaller, fast-growing trees. Prefabrication also minimizes construction waste generation.
The innate material efficiencies of floor trusses also promote sustainability. Less raw lumber is needed thanks to truss geometries that provide exceptional structural performance using less wood volume. Property engineered and prefabricated trusses also eliminate much job site wood scrap.
I-joists and floor trusses both enable resilient, long-lasting floor framing systems using the advantages of engineered wood products and designs. For typical residential builds, I-joists provide an easier to install and more customizable structural floor solution. Larger commercial projects often benefit more from the exceptional structural capacities, property efficiencies, and construction attributes of metal-plate-connected floor trusses.
By carefully weighing all the differentiators covered here based on your unique project specifications and builds, design teams can make informed, performance-driven decisions on selecting between I-joist or floor truss floor framing.