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MaterialCalc — Floor Truss vs I-Joist Cost Calculator

Estimate prepared 09/01/2026. Estimates only; verify against your plans before ordering.

Floor Truss vs I-Joist Cost Calculator

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Engineered members are cut to order, so this is small.

Result

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Floor trusses, I-joists and sawn lumber are not interchangeable at every span, and where two of them work the cheaper one is not always the cheaper job. Trusses cost more per foot and save a day of drilling for mechanicals. This prices all three against your span and tells you where sawn lumber stops being an option at all.

Assumptions used

These are the numbers behind the result. Where one of them is soft, the cost range widens rather than pretending to a precision the data does not have.

Lumber waste allowance
0.1

Cut-offs, crooked stock and the boards you set aside.

Standard industry overage — Industry standard, varies by supplier, checked 09/01/2026

Floor joist span table
360 L/360 deflection limit

Maximum clear span at 40 psf live load and 10 psf dead load — the normal residential floor. Your local code or an engineer has the final say.

American Wood Council, NDS span tables — Published product data, checked 09/01/2026

Prices verified 09/01/2026 (US national average, big-box retail shelf price and regional ready-mix quotes). Regional adjustment: Blended from RSMeans city cost index bands and BLS construction wage differentials.

The formula

Members = (floor length ÷ spacing) + 1. Total linear feet = members × span. Trusses and I-joists are priced per linear foot; sawn lumber is priced by the board, so the span is rounded up to stock lengths. Sawn feasibility comes from the span table for 2x12 at your spacing.

Worked examples

20 ft span at 19.2 in o.c.

Clear span: 20 Floor length: 32 Spacing: 19.2 Waste: 3

Beyond the reach of sawn 2x12, so the real choice is trusses against I-joists. Twenty-one members, 420 linear feet.

14 ft span at 16 in o.c.

Clear span: 14 Floor length: 28 Spacing: 16 Waste: 3

All three work at this span, and sawn lumber is usually cheapest on material. Whether it is cheapest overall depends on how much drilling the mechanicals need.

26 ft span at 24 in o.c.

Clear span: 26 Floor length: 40 Spacing: 24 Waste: 3

Well past sawn lumber and pushing I-joists. Floor trusses handle long spans at wide spacing better than anything else in wood.

Choosing materials

  • Open-web floor trusses let ducts, drains and wiring pass through without a single hole drilled. On a floor carrying HVAC, that saves more labor than the trusses cost extra.
  • I-joists have knockouts for small penetrations, but the flanges must never be cut and the web can only be opened where the manufacturer permits. A plumber who does not know that can ruin a floor in an afternoon.
  • Sawn lumber can be drilled, but only within limits: holes no larger than a third of the depth, at least 2 in from the edges, and never in the middle third of the span in the tension zone.
  • Both engineered options arrive straight and stay straight. Sawn 2x12 crowns, twists and shrinks, and a floor built from it needs sorting and crowning as you go.
  • Engineered members are made to order, so they carry lead time. Sawn lumber is on the shelf. If the schedule is tight, that difference can outweigh the price.

Common questions

Are floor trusses better than I-joists?

For running mechanicals, yes — open webs take full-size ducts without any cutting. I-joists are usually cheaper per foot and are lighter to handle. Trusses also span further at a given depth, which matters on long open floors.

How far can a floor truss span?

Commonly 20 to 30 ft depending on depth, and further with deeper trusses. Because they are engineered to order, the practical limit is what the manufacturer will design and what you can get delivered rather than a table figure.

When do I have to stop using sawn lumber?

Around 18 ft with 2x12 in southern pine at 16 in on center, and less in weaker species or at wider spacing. Past that no sawn dimension lumber reaches, and engineered framing is the only wood option.

Can I drill through I-joists?

Only through the web, only where the manufacturer allows it, and never through the flanges. Each maker publishes a hole chart showing permitted sizes and locations. Cutting a flange destroys the joist and it must be replaced.

Do floor trusses cost more than I-joists?

Usually yes per linear foot, often 30 to 50% more. The comparison above prices both for your actual quantity. The saving comes back in mechanical rough-in labor, which does not show up in a material quote.

Which option is quietest underfoot?

Deeper members at tighter spacing, whichever type. Both engineered options are stiffer than sawn lumber at the same depth, and both are far more consistent — squeaks usually come from fastening and subfloor detail rather than from the joist type.

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