Rafter Span per IBC 2024 Tables 2308.11.2

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): select Rafter, IBC Span Tables. Enter roof load (20 psf, or pg 30/50 snow), ceiling attached/detached, dead load, spacing, species, grade. Span = horizontal projection. Hc/Hr ratio for sloped ceiling. Multiple tables cover different load combinations.

Steps

1. 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, click the Rafter card.

2. Step 2: Select design method

   Design consideration: 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: In the "Select design method" section, click the "Span Tables per 2024 IBC Chapter 23 (Wood)" card.

3. Step 3: Live load, dead load, spacing

   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.

   In StructSuite: Under Roof load, select 20 psf. Under Ceiling condition, select Attached. Under Dead load, select 10 psf. Under Joist spacing, select 16. Under Species, select Douglas Fir-Larch. Under Grade, select #2. Under Joist size, select 2×8. IBC 2024 Tables 2308.11.2(1)–(6).

4. Step 4: 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 (horizontal projection) section, 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.