TJI vs floor trusses is the floor-system decision every custom home runs into, and it’s worth getting right — it drives your spans, your duct routing, how flat the floor feels underfoot, and even your stair length. This is the final post in our framing series (catch traditional vs modern framing, stack framing, and scissor trusses if you’re catching up). Here’s how I think about it on an Idaho build.
TJI vs Floor Trusses: The Basic Difference
The core of TJI vs floor trusses is solid web versus open web. A TJI (the brand name everyone uses for an I-joist) is an engineered joist shaped like a steel I-beam — flanges top and bottom with an OSB web between them — made in depths from 9½” up to 24″ and lengths up to 60 feet. An open-web floor truss is built from 2×4 chords and angled webs, like a little bridge, leaving open triangles all the way down its length. Both are engineered, made-to-order products; they just solve the floor differently.
TJI vs Floor Trusses on Span and Depth
On span and depth, TJI vs floor trusses favors trusses for long clear spans — they generally reach farther for a given depth and can eliminate an interior bearing wall and its footing, which opens up basement and main-floor layouts. The trade-off is that floor trusses are usually deeper (often 16″–24″), and a deeper floor system means taller walls, more siding and sheathing, and longer stair runs. TJIs tend to run shallower for the same job, which is why they win when floor-to-floor height or stair space is tight. Actual spans are always an engineering output — confirm them against the manufacturer’s tables (Weyerhaeuser’s ForteWEB for TJIs) and your local snow and live loads.
TJI vs Floor Trusses for Running Mechanicals
For running mechanicals, TJI vs floor trusses is where floor trusses shine. The open webs let your plumber, electrician, and HVAC crew run lines — including full-size duct — straight through the floor with no drilling, which keeps ductwork inside the floor instead of in a dropped soffit. With TJIs you drill the web, and only within the manufacturer’s strict knockout and hole-size chart — you never, ever cut the flanges — so big trunk ducts usually run below in a soffit. If your design is duct-heavy or you hate soffits, that one factor often decides it.
TJI vs Floor Trusses and the “Bouncy Floor”
When it comes to stiffness, TJI vs floor trusses is where the “bouncy floor” reputation comes from. I-joists draw most of the bounce-and-squeak complaints — builders on Fine Homebuilding describe a poorly specced I-joist floor as feeling “like walking across a drum head.” But here’s the honest truth: that’s almost always a specification problem, not a flaw in the product. Spec for performance instead of just minimum depth and spacing, glue and screw the subfloor, and TJI floors feel rock-solid. Floor trusses of the same depth are generally a touch stiffer out of the gate, but either system squeaks if the subfloor isn’t glued and screwed right.
TJI vs Floor Trusses and the Fire Code You Can’t Skip
On fire, TJI vs floor trusses lands in the same place: both fail fast and both trigger the same code requirement. Unprotected engineered floors — thin I-joist webs and truss connector plates alike — lose capacity quickly in a fire and can collapse suddenly, which is why IRC R501.3 (now R302.13) requires a membrane on the underside: ½” gypsum board, ⅝” wood structural panel, or equivalent. The exceptions are a sprinkler system or solid dimensional lumber 2×10 or larger — and the critical catch is that the ICC says the 2×10 exception does not apply to trusses. So a deep floor truss still needs that membrane unless the space is sprinklered. Plenty of builders get surprised by this; don’t be one of them.
TJI vs Floor Trusses: Cost and How I Choose
On cost, TJI vs floor trusses usually shakes out with I-joists cheaper up front — figure roughly $5–$12 per linear foot installed for TJIs versus about $8–$22 for floor trusses, though both swing hard with depth, span, and the 2026 market (verify with your local supplier). The “deeper is cheaper” argument for trusses is real on the truss line item but can get eaten by taller walls, longer stairs, and more trades, so I price the whole assembly, not just the joist. How I choose: floor trusses when I want long clear spans, no interior bearing wall, and clean mechanical runs; TJIs when the budget’s tight, the floor depth has to stay shallow, and the crew wants lighter, easier handling. There’s no universal winner — only the right call for your plan, your spans, and your mechanicals.
Not Sure Which Floor System Fits Your Plan?
If you’re building in Eastern Idaho or Teton Valley and want a builder who’ll spec the floor system around your actual layout and loads — not just default to whatever’s quickest — get in touch through our contact page. That wraps our framing series; start back at traditional vs modern framing for the big picture.
Leave a Reply