A floor truss is an engineered floor framing member using triangulated top and bottom chords connected by open web members, typically metal or wood, creating open spaces within the truss depth that ductwork, plumbing, and wiring can pass through freely.
This open web design distinguishes floor trusses from solid I-joists, offering a genuine advantage for mechanical system routing that a solid-web product can’t match without cutting holes.
Because floor trusses are custom-engineered for each specific project’s span and load requirements, they typically arrive on site pre-manufactured to exact specifications rather than being adjusted in the field.
What Does a Floor Truss Involve?
- Triangulated top and bottom chords
- Open web members, typically metal or wood
- Custom engineering for the specific project’s spans and loads
- Open cavities allowing mechanical systems to pass through
Why Are Floor Trusses Important?
The open web design significantly simplifies routing ductwork, plumbing, and electrical wiring through a floor system, since these systems can pass directly through the truss’s open spaces rather than requiring holes cut through a solid member. This practical advantage makes floor trusses particularly popular in homes with extensive mechanical systems or where floor depth needs to accommodate multiple utility runs simultaneously.
Because floor trusses are custom-engineered and manufactured off site to precise specifications, field modification is generally not permitted without manufacturer approval, unlike solid lumber that can be more easily adjusted on site if needed. This practical advantage often outweighs the higher upfront cost compared to solid engineered lumber alternatives. This flexibility continues to make it a favorite among builders working with complex mechanical layouts.
Floor Truss vs. I-Joist
A floor truss uses an open web design allowing utilities to pass through freely. An I-joist uses a solid web, offering excellent strength and stiffness but requiring holes to be cut, following manufacturer guidelines, for any utility penetrations.