Example
A gable roof with 20 psf roof live load, 10 psf dead, ceiling attached to rafters. Rafters 16 in. O.C., Douglas Fir-Larch #2. Need 2×8 for 14 ft horizontal span or select size. Per IBC 2024.
How StructSuite solves this
StructSuite's free beam design calculator applies IBC 2024 Tables 2308.11.2(1)–(6): open the Floor Joist, Ceiling Joist & Rafter module; under Select member type choose Roof Joist & Rafter; under Rafter design basis select Common lumber species. Enter roof load (20 psf, or pg 30/50 snow), ceiling attached/detached, dead load, rafter spacing and size, species, grade. Span = horizontal projection. Hc/Hr ratio for sloped ceiling. Multiple tables cover different load combinations.
Steps
- Step 1: Select member type
Design consideration: Rafters carry roof dead + live/snow. Attached ceiling acts as rafter tie—restrains thrust. Slope affects axial: steeper = more axial, less flexure. Span = horizontal projection (not slope length). 2×6–2×10 common; steep pitch or heavy snow needs larger.
In StructSuite: In the "Select member type" section at the top, select the **Roof Joist & Rafter** radio button.
- Step 2: Roof load, ceiling condition, dead load
Design consideration: 20 psf roof live for pg < 30; pg 30/50 for snow. Dead 10 psf = shingles + sheathing; 15–20 for tile, slate. Attached ceiling typical for habitable space. Detached (cathedral) uses Hc/Hr ratio—reduces span capacity. Heavier snow zone = smaller max span. IBC tables for pg ≤ 50 psf. Snow pg from ASCE 7-22 maps: Northeast, Rockies 50+ psf; Southeast 20–30. NDS when pg > 50, custom slope, or LVL. Horizontal span: 14 ft projection = 14 ft in table regardless of slope.
In StructSuite: Under **Rafter design basis**, select **Common lumber species**. Under **Roof load**, select the radio labeled **Roof live load = 20 psf (pg(asd) < 30 psf)**. Under **Ceiling condition**, select the radio labeled **Ceiling attached to rafters (L/Δ = 240)**. Under **Dead load**, select the radio labeled **Dead load = 10 psf**. Under **Rafter spacing (inches)**, select **16**. Under **Rafter size**, select **2×8**. Under **Species**, select **Douglas Fir-Larch**. Under **Grade**, select **#2**. IBC 2024 Tables 2308.11.2(1)–(6).
- Step 3: Span check
Design consideration: 2×8 at 16 in., 20 psf roof, attached ceiling: ~14–16 ft horizontal. pg 50 psf cuts span ~25%. Steeper slope (6/12 vs 4/12) may reduce capacity—axial increases. Regional snow load from ASCE 7 Figure 7.2-1.
In StructSuite: In the **Rafter span** section (horizontal projection per the code note in the UI), enter **14** in the ft box and **0** in the in. box. The result will show SATISFACTORY or NOT SATISFACTORY per IBC 2024 Tables 2308.11.2(1)–(6).
Live design (pre-filled)
The form below is the real StructSuite module with example data loaded. Display only—values cannot be changed.