ASCE 7-22 Snow Loads in IBC 2024: Strength-Based Design Requirements

Overview

The 2024 International Building Code (IBC) introduces significant changes to snow load design by adopting ASCE 7-22, which transitions from traditional ASD-based values to strength-based snow loads.  Understanding these updates is essential for accurate, code-compliant structural design and proper input into software such as ForteWEB® and Javelin®

It is critical that ForteWeb® and Javelin® users understand that ground snow load (p_g) is now a strength-level load, not an allowable-level load under the 2024 IBC

• Previous editions of IBC/ASCE 7 (2021 IBC/ASCE 7-16 and earlier) used ground snow loads (p_g) based on a uniform-hazard 50-year mean recurrence interval (MRI) with a load factor of 1.6 for strength-level (LRFD) design.
• In ASCE 7-22, p_g values are based on uniform-reliability (strength-level) values and the LRFD snow load factor is effectively reduced from 1.6 to 1.0.
• This is a major change in how snow loads appear in load combinations.
• This change aligns snow loads with how other environmental loads (like wind and seismic) are treated in load combinations.
• ASCE Hazard Tool can provide the project ground snow load, p_g, if you enter the address, select ASCE 7-22, Risk category (II for residential) and check snow load.
• 2024 IBC does allow 0.7 x snow load when calculating deflection. Refer to table 1604.3, footnote j of 2024 IBC.
• Minimum snow load for low sloped roofs was 20 psf and is now 30 psf for Risk Category II. Refer to the table below (ASCE 7-22)

• For more information on the development and history behind this code change, refer to Structure Magazine “Ground Snow Loads For ASCE 7-22” article https://www.structuremag.org/article/ground-snow-loads-for-asce-7-22/

Strength Design or Load and Resistance Factor Design (LRFD)

• Snow load is no longer multiplied by 1.6 in LRFD combinations
• Example (simplified):
  • 2021 IBC and earlier: 1.2D + 1.6S
  • 2024 IBC: 1.2D + 1.0S

Allowable Stress Design (ASD)

• Snow load is adjusted through conversion factors. The 0.7 factor converts strength-level snow loads back to an ASD-equivalent level for allowable stress design.
• Example (simplified):
  • 2021 IBC and earlier: 1.0D + 1.0S
  • 2024 IBC: 1.0D + 0.7S

Why This Matters in ForteWeb and Javelin

• Users need to be aware of whether the snow loads provided by the designer of record or jurisdictions have been updated to reflect strength-level values from 2024 IBC. If so, verify 2024 IBC is selected under the Job Settings for the code version. If not, use 2021 IBC or earlier code for the correct load combination for an allowable level snow load.

  

• As an additional verification, check the Report tab to make sure it matches the code for the snow load input.

  

• For some low roof snow loads, combinations with roof live load may control the design.  It is advised, when using 2024 IBC building code, to input the roof live load as well as the roof snow load into ForteWEB and Javelin.  The software will run through all load combinations to find the controlling combination.

2024 IRC Snow Load Changes

• Since wood design is ASD in the US, 2024 IRC updated the ground snow loading maps but kept ground snow load in an ASD value called p_g(asd). Refer to figure R301.2(3) from 2024 IRC. This figure is meant to be used with prescriptive sizing tables only. Do not input this IRC ground snow load into ForteWeb or Javelin with 2024 IBC code selected. The wrong load combination factors will be applied, and your structure will be under designed.
• Span tables in 2024 IRC have not changed.  Use p_g(asd) with the published load tables.
• Another way to find the snow load is to use ASCE Hazard Tool which can provide the project ground snow load, p_g, if you enter address, select ASCE7-22, Risk category (II for residential) and snow load. P_g is an LRFD snow load and can be directly plugged into ForteWeb and Javelin when 2024 IBC is selected.
•  To use TJ literature, multiply your 2024 IBC/ASCE 7-22 snow loads (p_g) by the ASD conversion factor of 0.7 (or use p_g(asd) from 2024 IRC) and use that value in the span tables. This is noted in bullet 3 of the General Notes. 

(TJ-4000 TJI Specifier's Guide, pg. 13)

Summary:

• 2024 IBC/ASCE 7-22 has shifted snow loads to be a strength-level loads. This drastically changes how snow is used in load combinations.
• Selecting the correct IBC version for your snow load input  is critical for the design of roof members.
• It is advised to input both roof live load and roof snow load when using 2024 IBC building code.
• Do not input IRC p_g(asd) values into ForteWeb or Javelin when 2024 IBC is selected. This will apply incorrect load combination factors and can result in unconservative design.
• ASCE Hazard Tool can provide the project ground snow load, p_g, but always check with local jurisdictions. P_g can conservatively be plugged directly into ForteWeb and Javelin for the roof snow load
• TJ literature is in ASD. Multiply 2024 IBC/ASCE 7-22 snow loads (p_g) by the ASD conversion factor of 0.7 and use that value to compare to the TJ literature span tables.

Additional resources:

Techtalk webinar, see webinar titled “2024IBC Snow Load Changes”: https://www.weyerhaeuser.com/woodproducts/software-learning/software-training/software-training-schedule/