b"YOUR TOOLKIT FOR BUILDING EXCELLENCEload using a uniform-hazard approach with a 50-yearA new table showing the upper limit of minimum mean recurrence interval (MRI) and a 1.6 load factorsnow load, p m , maxhas been added, providing specific (load and resistance factor design, LRFD) based onvalues for each risk category.available historical data. Building design criteria underUnbalanced snow load and snow drift provisions have this method focused on the probability of a snow eventbeen revised.A Winter Wind Parameter, W 2 , defined exceeding the predicted snow loads. This resulted inas percent of time wind speed is above 10 mph during nonuniform roof reliability, leading to under-designedwinter (ASCE 7-22, Figure 7.6-1), is incorporated roofs in some regions and over-designed roofs ininto the equations, making drift calculations more others. This inconsistency in reliability meant that thelocation-specific.level of safety against snow-induced collapse varied significantly across the nation, despite adherence toRain-on-snow surcharge load provisions have been the same standard. Furthermore, the uniform-hazardupdated to address new ultimate snow load values.approach didn't directly correlate the predicted ground snow load to the actual structural capacity of the roof,Snowloadchangesalsoimpactseismicload potentially leading to inefficient use of materials andcalculations. Specifically, when the flat roof snow resources. load exceeds 45 psf, 15% of the uniform design snow load must be added to the effective seismic weight. In The move to a reliability-targeted approach in ASCEASCE 7-16, these parameters were 30 psf and 20%, 7-22 addresses these inconsistencies by directly linkingrespectively.the design snow load to an acceptable probability of structural failure. This provides a more consistentPotential for miscommunication and errorslevel of safety for all building occupancies nationwide,The updated snow load requirements in ASCE 7-22 ensuring that the likelihood of collapse due to snowintroduce several potential areas for miscommunication loads is more uniform. The revised ground snowamong engineers, building officials, and designers. load maps incorporate 30 additional years of weather data, increasing accuracy and significantly reducingDifferent Interpretations of Load Values:Some case-study areas. professionals may mistakenly use old ground snow Changes that affect everyday calculations load values or fail to distinguish between ultimate and service-level loads, particularly since both Designers will now use separate ultimate ground snoware still referenced in various codes and design loads for each risk category.The site-specific valuesprograms.can be found at https://ascehazardtool.org. Software and Calculation Updates:Design software Designers will spend less time searching for snow loadand calculation templates may not be updated data in case-study areas.Ground snow load values areimmediately, leading to discrepancies in applied available for most areas.The number of case-studyloads or missed new requirements.Selecting the regions has been reduced by approximately 90%. correct version of the ASCE 7 standard in design software has become even more critical.The snow load factor is reduced to 1.0 in LRFD loadASCE 7-22 standard with 2021 IBC or older combinations and to 0.7 in ASD load combinationscodes:While ASCE 7-22 forms the basis for the 2024 (for example: 1.2D+1.0S (LRFD), 1.0D+0.7S (ASD)). International Building Code, adoption timelines The snow importance factor, I s, has been removedvary by state and jurisdiction.Earlier IBC model from all equations. codes reference ASCE 7-16 or older versions.Some The thermal factor, C t, criteria have been updated.states, like Florida and Virginia, still operating Table 7.3-3, found in ASCE 7-22, shows new thermalunder the 2021 International Building Code have factors for different insulation and ground snow loadalready adopted ASCE 7-22. The designer should scenarios for heated structures with unventilated roofs. review all state and local amendments to confirm which version of ASCE 7 is required for a specific The minimum snow load, p m , criteria have changed.project.continued on page: 26 FRAME BUILDER - VOL6 4 / 25"