I-Joist Selection Calculator

About the I-Joist Selection Calculator

Wood I-joists (also called I-beams or TJI joists, after the Weyerhaeuser brand) are the standard for modern residential floor framing. They consist of an OSB or plywood web sandwiched between top and bottom LVL or solid sawn flanges, creating a lightweight, strong member that can span farther than solid lumber at the same depth.

This I-joist selection calculator helps you choose the right series and depth for your floor based on the span and OC spacing. It uses typical residential I-joist span data for 40 psf live / 20 psf dead load, which is the standard for most living areas. The calculator compares available depths (9.5″, 11.875″, 14″, 16″) at common spacings (12″, 16″, 19.2″, and 24″ OC).

I-joists are lighter, straighter, and more dimensionally stable than solid sawn joists. They don't twist, bow, or shrink, which results in quieter, flatter floors. Their long lengths (up to 60') reduce or eliminate the need for splicing.

When This Page Helps

Choosing the right I-joist depth and spacing is essential for floor performance. Too shallow and the floor bounces; too deep wastes money and building height. This calculator makes the comparison instant.

How to Use the Inputs

1. Enter the clear span of the floor (feet).
2. Select the OC spacing.
3. Compare the available I-joist depths and their pass/fail status for your span.
4. Select the shallowest passing depth for economy, or a deeper one for a stiffer floor.
5. Verify with the I-joist manufacturer's published span tables.

Example Calculation

Tips & Best Practices

• Never cut, notch, or bore holes in I-joist flanges—it destroys the structural capacity.
• Web holes must follow the manufacturer's guidelines (typically centered, max diameter specified per depth).
• I-joists require web stiffeners at concentrated loads and bearing points.
• Use rim boards (1.125″ LVL or 1″ OSB rim) at the perimeter—solid lumber rim joists can shrink differentially.
• I-joist floors can feel bouncy if the span-to-depth ratio is too high. Consider upgrading one depth for occupant comfort.
• Always brace the top flange during construction until the subfloor is attached.

I-Joist Floor Performance

For the best floor feel, select an I-joist one depth larger than the minimum. For example, if an 11.875″ I-joist just barely makes the span, consider using a 14″ joist. The extra depth significantly increases stiffness and virtually eliminates occupant complaints about floor bounce.

I-Joist Handling and Storage

I-joists are fragile when not braced. Store them flat on a dry surface or upright on a flat surface. Never lean them at an angle. During installation, immediately install rim board and temporary bracing—an unbraced I-joist can buckle laterally under its own weight.

Fire Considerations

I-joists have less fire resistance than solid sawn joists due to the thin OSB web. The web can burn through in as little as 4–6 minutes. In some jurisdictions, I-joist floors require a gypsum ceiling (fire barrier) below. Check local codes.

Frequently Asked Questions

• What is the difference between TJI 150, 210, and 230?

  These are Weyerhaeuser's I-joist series with increasing stiffness. TJI 150 is the lightest-duty (shortest spans). TJI 210 is the standard residential series. TJI 230 is heavier-duty for longer spans or higher loads. Other manufacturers have equivalent series with different names.

• Can I use I-joists for roofs?

  Yes, I-joists are used for roof framing, especially for flat or low-slope roofs. Spans are typically longer than for floors because roof loads are lighter (20 psf LL for most areas). Web stiffeners are required at bearing points.

• Why is L/480 used instead of L/360?

  I-joist manufacturers and many engineers use L/480 for floor live load (instead of the code-minimum L/360) to provide a stiffer, more comfortable floor. L/480 reduces the perceptible bounce that occupants dislike.

• Can I drill holes in an I-joist web?

  Yes, within the manufacturer's guidelines. Each depth has a maximum round-hole diameter and location requirements (centered vertically, adequate distance from bearing points). Never cut or notch the flanges under any circumstances.

• How heavy is an I-joist?

  I-joists weigh 2.5–4.5 lbs per lineal foot depending on the depth and series. A 16-ft 11.875″ I-joist weighs about 48 lbs—easy for one or two workers to handle, compared to 80+ lbs for a 2×12×16.

• Do I-joists need blocking?

  I-joists require blocking or bridging at supports and may need mid-span blocking for bracing during construction. Squash blocks (short blocks the same depth as the I-joist) are required at bearing points where heavy point loads are transferred.