Cold-formed steel soffit framing
Soffit and canopy framing of cold-formed C-section joists spanning from the wall to a line of hangers, under dead load and wind on the soffit in both directions, with the hangers to the structure above and a kicker taking the fascia's horizontal wind. To AISI S100-16 with the loads combined by ASCE 7-22 2.3.1 or 2.4.1.
Inputs of the soffit framing #
- Soffit joists: an SSMA designation or custom dimensions, Fy, Fu, the spacing, the span from the wall to the hanger line, and the slope (the dead load is taken normal to the joist by cos θ).
- Bracing: the soffit board is on the bottom flange. Under net downward load the top flange is in compression and is braced at the bridging spacing you enter (0 = unbraced over the span), with Cb. Under net upward load the board braces the compression flange; its rotational restraint kφ (AISI S240-20 B1.2.2.3 and its Appendix 1) is your entry, 0 if unknown.
- Loads: the dead load and the wind pressure on the soffit, down and up: your ASCE 7-22 Chapter 30 components and cladding values (soffits take the pressure of the wall or overhang zone they adjoin, your reading). The deflection uses your wind factor (0.42, IBC Table 1604.3 footnote) and your limit.
- Hangers: an SSMA C-section, its yield stress, length (pinned ends, K = 1.0) and spacing along the hanger line.
- Kicker: an SSMA C-section at an angle from horizontal, from the hanger's foot up to the structure, for the fascia's horizontal wind (fascia height and pressure) in both directions.
- Screws at each end of a hanger or kicker.
Auto-design varies the SSMA joist, the hanger and the kicker (lightest first) and the screws at their ends. Span, spacing, loads and limits are kept.
Checks performed #
| Check | Basis |
|---|---|
| Flexure, net downward (top flange braced at the bridging) | S100 F2, F3, F4 (Lm = the bracing spacing) |
| Flexure, net upward (the board's flange in compression) | S100 F3 with Fn = Fy and F4 with kφ (S240 B1.2.2.3, applied to the soffit: to confirm) |
| Shear at the supports | S100 G2 |
| Deflection under D ± 0.42 W at the service section | IBC Table 1604.3 (your limit), S100 L1 |
| Hanger in tension and compression (joist reaction and the kicker's vertical part) | S100 D2, E2, E3 |
| Kicker in compression and tension | S100 D2, E2, E3 |
| Screws at the ends of the hangers and the kicker | S100 J4.3.1, J4.3.2 |
Limitations #
- The wind pressures on the soffit and fascia are your entries; this type does not compute ASCE 7 pressures.
- Simple span only. The joist's inner support (wall, ledger or clip), the structure above, the board and its fasteners, and web crippling where the reaction does not pass through screws are not designed.
- The hangers and kicker are pinned struts with K = 1.0 about every axis; a carrier member between hangers spaced wider than the joists is yours to design.
- The axial part of the dead load along a sloped joist is reported, not added to the joist.
Verification examples #
Verification status: 10 values compared in 1 example (0 published, 1 hand calculations from the cited equations): 10 within tolerance, 0 recorded deviations. No published example: every value is a hand calculation. That checks the program against this reading of the code, not the reading itself. Code basis: not yet recorded for this module.
No published worked example of soffit framing is in the free library. The values are hand calculations of the combinations, the statics, the hanger and kicker forces, S100 J4.3.1 and the deflection.