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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.

Scissor trusses are how you get that vaulted, cathedral ceiling without paying for a big structural ridge beam — and they’re one of the most-requested features I build into custom homes in Teton Valley and Eastern Idaho. This is part three of our framing series (see traditional vs modern framing and stack framing for the foundation). Here’s what they actually do, and the snow-country details that bite people who don’t plan for them.

What Are Scissor Trusses?

Scissor trusses are roof trusses with a sloped bottom chord instead of a flat one, so the underside follows the roofline up to a vault and the truss itself carries the load to the bearing walls — no structural ridge beam required. The two chords cross like a pair of scissors, which is where the name comes from. You get the open, vaulted look across the whole span while the truss does the structural work hidden inside the roof.

Scissor Trusses and the Half-Pitch Rule

The most important thing to understand about scissor trusses is that the ceiling pitch is roughly half the roof pitch — you can’t vault the ceiling to match the roof. The truss needs depth between the top and bottom chords to carry load, so a 6/12 roof typically gives you about a 3/12 ceiling. Common engineering guidance keeps the ceiling slope at or under half the roof slope and wants at least a 2/12 difference between the chords. If you want a dramatic vault, you start with a steeper roof. People who skip this step are disappointed when the “vault” comes back shallower than they pictured.

Scissor Trusses Push on Your Walls (Thrust)

Because scissor trusses have no flat bottom chord tying the walls together, they push outward on the walls under load — a force called horizontal thrust. That’s not a flaw, it’s physics, and it has to be engineered for. The standard fix is a pinned bearing at one end and a roller (slotted) bearing at the other so the truss can move horizontally without prying your walls apart. This is exactly why you don’t buy a scissor truss off a generic plan and drop it on your walls — the connection detail matters as much as the truss.

Scissor Trusses and Drywall Cracking

The complaint you’ll read about scissor trusses on builder forums is drywall cracking, and it’s almost always a movement issue, not a structural failure. A scissor truss deflects more — and differently — than an adjacent flat-bottom truss, and that “differential deflection” opens hairline cracks where they meet, often seasonally as humidity changes. Here’s the catch: ANSI/TPI 1, the truss standard, doesn’t set a differential-deflection limit — it makes the building designer specify one. The mitigation is detailing: slotted truss-to-wall clips that let the truss move, and keeping drywall fasteners back about 16 inches from the wall-ceiling intersection so the panel can float. Plan it and you avoid the cracks. Ignore it and you’ll be chasing them every spring.

Scissor Trusses, Insulation, and the Raised Heel

In a cold climate, scissor trusses live or die on insulation, and the single biggest regret people report is not planning for it. Vaulted geometry pinches the insulation cavity right where the roof meets the wall — the coldest, most ice-dam-prone spot — so you spec a raised (energy) heel that carries full insulation depth out over the top plate. In Climate Zone 6, which covers most of Eastern Idaho, the code wants roughly R-49 in the ceiling, reducible to R-38 where insulation fully covers the plate, which a raised heel makes possible. One more field note: blown cellulose tends to slide on slopes steeper than about 4/12 to 5/12, so on a steeper vault you plan the insulation type around the slope, not after.

Scissor Trusses and Idaho Snow Load

For scissor trusses in Eastern Idaho, snow load is the number that drives the whole design, and it’s site-specific. Teton County alone sets minimum roof snow loads of 85 psf below 6,600 feet and 100 psf above it, plus drift, and mountain sites run higher — Idaho ground snow loads range from around 20 psf in the south to well over 200 psf in the high country. A scissor truss that spans fine in a mild climate may not pencil here at all, which is why every one we build is engineered to the specific site and the local building department’s adopted load. Never trust a span you saw on someone else’s project. We cover the floor side of this in the TJI vs floor trusses post.

What Scissor Trusses Cost in 2026

On price, scissor trusses typically run about 20–30% more than a standard flat-bottom truss, and in 2026 that premium holds. The added cost buys the sloped-chord engineering, the thrust detailing, and usually a raised heel for insulation — all of which you want anyway in this climate. Lead times vary by plant and season, so on a snow-country build I get the truss package engineered and ordered early rather than letting it become the thing that holds up your dry-in before winter.

Planning a Vaulted Ceiling?

If you want a vaulted, open ceiling done right for Idaho snow and Idaho winters, reach out through our contact page and we’ll talk through pitch, insulation, and budget before anything gets ordered. Last in the series: TJI vs floor trusses — picking the right floor system.