Example
An attic with limited storage (20 psf live load, 10 psf dead) needs ceiling joists at 16 in. O.C. Douglas Fir-Larch #2. Verify 2×6 for 12 ft span or select size for 14 ft. Per IBC 2024 Chapter 23.
How StructSuite solves this
StructSuite's free structural design software applies IBC 2024 Tables 2308.11.1(1)–(2): open the Floor Joist, Ceiling Joist & Rafter module; under Select member type choose Ceiling Joist; under Ceiling joist design basis select Common lumber species. Under Live load and dead load, select Uninhabitable attics with limited storage (20 psf live, 10 psf dead). Enter spacing, species, grade, and ceiling joist size as in the example. L/240 deflection. Two load cases: 10 psf no storage (larger spans) vs 20 psf limited storage (more conservative).
Steps
- Step 1: Select member type
Design consideration: Ceiling joists support ceiling weight and provide rafter tie—resist outward thrust. Lighter than floor joists. Span controlled by LL: no storage (10 psf) allows ~40% longer span than limited storage (20 psf). 2×6 typical; 2×8 for wide attics.
In StructSuite: In the "Select member type" section at the top, select the **Ceiling Joist** radio button.
- Step 2: Attic live load, dead load, spacing
Design consideration: 20 psf limited storage is conservative; many attics use 10 psf. Dead 10 psf = drywall + insulation. Spacing 16 in. most common. Species: DF-L, SPF, Southern Pine—regional availability. 2×6 at 16 in., 20 psf: ~11–12 ft max; 10 psf: ~14 ft. IBC Tables 2308.11.1 prescriptive. No storage = walkway only; limited storage = 20 psf for boxes, HVAC. If HVAC unit concentrated, NDS with point load. L/240 deflection—less strict than floor L/360.
In StructSuite: Under **Ceiling joist design basis**, select **Common lumber species**. Under **Live load and dead load**, select the radio labeled **Uninhabitable attics with limited storage, live load = 20 psf (L/Δ = 240), dead load = 10 psf**. Under **Ceiling joist spacing (inches)**, select **16**. Under **Ceiling joist size**, select **2×6**. Under **Species**, select **Douglas Fir-Larch**. Under **Grade**, select **#2**. IBC 2024 Tables 2308.11.1(1)–(2), L/240.
- Step 3: Span check
Design consideration: Span vs load trade-off: 20 psf limits span; 10 psf extends it. HVAC units, access stairs add point loads—tables assume uniform. For 12 ft with 20 psf, 2×6 often works; 14 ft may need 2×8 or 10 psf.
In StructSuite: In the Ceiling joist span section, enter 12 in the ft box and 0 in the in. box. The result will show SATISFACTORY or NOT SATISFACTORY per IBC 2024 Tables 2308.11.1(1)–(2).
Live design (pre-filled)
The form below is the real StructSuite module with example data loaded. Display only—values cannot be changed.