Select the right I-joist depth and series for your floor span and spacing. Compare TJI and other I-joist products by span capability.
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.
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 tool makes the comparison instant. Data-driven calculations reduce financial risk by ensuring that material orders, labor estimates, and project budgets reflect actual requirements rather than rough approximations.
Max span = from manufacturer tables (depends on joist series, depth, spacing, and load) Typical residential: 40 psf LL + 20 psf DL = 60 psf total Deflection limit: L/480 for floor live load (better than L/360 for reduced bounce)
Result: 11.875″ I-joist at 16″ OC (max span ~19 ft)
At 16″ OC: 9.5″ TJI150 spans ~15 ft (not enough). 11.875″ TJI210 spans ~19 ft (adequate). 14″ TJI230 spans ~21 ft (extra margin). Choose 11.875″ for economy or 14″ for a stiffer floor.
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-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.
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.
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.
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.
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.
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.
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.
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.