Example
A residential bedroom has floor joists spanning between bearing walls. Given: live load 30 psf (IBC Table 1607.1—sleeping areas); dead load 10 psf (joists, subfloor, carpet); joist spacing 16 in. O.C.; lumber Douglas Fir-Larch No. 2 (DF-L #2); joist size 2×8. The span from bearing to bearing is 12 ft 6 in. Verify that 2×8 DF-L #2 at 16 in. O.C. is adequate for this span, or determine the maximum permitted span. If the span were 14 ft, select the minimum joist size. Per IBC 2024 Chapter 23, Tables 2308.8.2.1(1) and 2308.8.2.1(2). L/360 deflection per IBC Table 1604.3.
How StructSuite solves this
StructSuite's free structural design software applies IBC 2024 Tables 2308.8.2.1(1) and 2308.8.2.1(2). Open the Floor Joist, Ceiling Joist & Rafter module. Under Select member type, choose Floor Joist. Under Floor joist design basis, select Common lumber species. Enter: Live load 30 psf (residential sleeping), Dead load 10 psf, Joist spacing 16 in., Species Douglas Fir-Larch, Grade #2, Size 2×8. In Floor joist span enter 12 ft 6 in. The result shows SATISFACTORY or NOT SATISFACTORY. For 14 ft span, enter 14 ft 0 in. and increase size to 2×10 if 2×8 fails. This is the most common daily check for residential plan review and permit submittals.
Steps
- Step 1: Select member type
Design consideration: Floor joists carry gravity; span length squared drives moment (M ∝ L²). Longer spans need deeper members or tighter spacing. Residential: 2×8, 2×10 common; 2×6 for short spans. 30 psf bedrooms; 40 psf living. Ceiling joist/rafter use different IBC tables.
In StructSuite: In the "Select member type" section at the top, select the **Floor Joist** radio button.
- Step 2: Live load, dead load, spacing
Design consideration: 30 psf = sleeping; 40 psf = living. Higher live reduces max span. Dead: 10 psf = joist + subfloor + carpet; 20 psf = tile. Spacing 16 in. most common; 24 in. cuts span ~15%. Species: DF-L West; Southern Pine Southeast; SPF Northeast/Canada. IBC tables prescriptive—no calcs when within limits. NDS when loads exceed tables, point loads, engineered lumber (LVL, I-joist), or custom spacing. Plan reviewers often require table compliance for fast permit.
In StructSuite: Under **Floor joist design basis**, select **Common lumber species**. Under **Live load**, select the radio labeled **Residential sleeping areas, live load = 30 psf, L/Δ = 360**. Under **Dead load**, select the radio labeled **Dead load = 10 psf**. Under **Joist spacing (inches)**, select **16**. Under **Species**, select **Douglas Fir-Larch**. Under **Grade**, select **#2**. Under **Joist size**, select **2×8**.
- Step 3: Span check
Design consideration: 2×8 DF-L #2 at 16 in., 30 psf LL: max span ~12 ft 6 in. 2×10 extends to ~15 ft. Deflection L/360 often governs long spans. Span length ∝ 1/√load—doubling LL roughly halves max span. Exceeding table by 1 in. can fail; use next size or NDS. Regional species availability affects choice.
In StructSuite: In the Floor joist span section, enter 12 in the ft box and 6 in the in. box. The result will show SATISFACTORY or NOT SATISFACTORY per IBC 2024 Tables 2308.8.2.1(1)–(2).
Live design (pre-filled)
The form below is the real StructSuite module with example data loaded. Display only—values cannot be changed.