Significant changes have been made to the ground snow loads in Chapter 7.  What prompted these changes and why were they necessary?

In the February 2026 SEU Session, Scott Russell, SE, PE, from Vulcraft, presented ASCE/SEI 7-22 Snow & Rain Loading with Suggestions on Joist Specification.  Scott described significant updates to the snow provisions in ASCE 7-22 and identified new provisions for thermal factors, snow drift heights and windward drifts widths and how to apply them.  He also explained the revised rain load calculation methodology in Chapter 8 and reviewed how to specify joists and joist girders for these new changes to ASCE 7-22.

The primary purpose of the changes in Chapter 7 of ASCE 7-22 aim to achieve uniform failure probability through a reliability-targeted ground snow load.  While previous ground snow load maps were based on too few data samples to be accurate for local use, modern snowfall data collected throughout the last 40 years include 500,000+ ground snow load values which have been scrutinized and evaluated.  The data from each weather station is used to produce reliability-targeted loads that seek to estimate the probability that the Random Resistance minus the Random Roof Load is less than zero, as shown in the slide below.

As you can see at the top of the graphs, the different Coefficient of Variation can drive different Mean Recurrence Interval values which is why it is not accurate and efficient to use the same MRI value of 50% throughout the entire United States.  This variation can be shown in the graphs below, which note the differences in snow behavior in three different cities depending on typical snow behavior vs extreme snow behavior. 

As a result of this newer data set being collected and analyzed, four new ground snow loads maps have been included in ASCE 7-22, one for each of the four Risk Categories.  The ASCE Hazard Tool is the easiest and most accurate way to establish the new ground snow load for your building location.  This major update to Chapter 7 in ASCE 7-22 will help eliminate the need for local authorities to adopt other snow load guidelines, and provide more appropriate loads based on eco-regions rather than arbitrary state lines.