Rafter Span per IBC 2024 Tables 2308.11.2

Summary: Check rafter span for gable roof with attached ceiling per IBC 2024 Tables 2308.11.2(1)–(6) for roof load, ceiling condition, and species. A gable roof…

Overview

Check rafter span for gable roof with attached ceiling per IBC 2024 Tables 2308.11.2(1)–(6) for roof load, ceiling condition, and species.

Problem statement

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.

Workflow in StructSuite

StructSuite's free beam design calculator applies IBC 2024 Tables 2308.11.2(1)–(6): open the Floor Joist, Ceiling Joist & Rafter module, select Rafter. 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.

Design considerations (excerpt)

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.

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…

Related terms

• StructSuite
• structural engineering
• design example
• framing
• IBC
• rafter gable attached

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