With the New Year comes new International codes, IBC and IRC 2018 (referred to as the I-Codes), and fortunately, few changes to truss designs. These changes are the result of the revised design criteria contained in ASCE 7–16, which IBC 2018 relies upon.
Very few jurisdictions will adopt the new I-Codes early in 2018; most will remain under IBC/IRC 2015 and TPI 2014 until much later. And some select projects may be “grandfathered” and still allow use of IBC/IRC 2012 and TPI 2007. Be aware that there are more significant truss design changes when upgrading from the 2012 International Codes, since designs must comply with TPI 2014, which up-sizes plates at several joint types.
Whenever there are relevant changes in any of the four major code bodies, truss design will most likely be affected:
- ASCE 7 codes specify the magnitude and application of loads – wind, snow, earthquake, etc. – prescribed by the American Society of Civil Engineers. The 2016 revision, ASCE 7–2016, has again modified the snow and wind maps from the 2010 Code, and permits interpolation between zones. However, local building departments normally establish minimum snow and wind loads for their jurisdictions which take precedence, and may be higher than those found in ASCE 7. Revised codes have been published in 2002, 2005, 2010, and 2016.
- ANSI TPI codes specify design methods for truss members and joints, and have increasingly refined (and complicated) the methodology. Changing from the 2012 to the 2015 or 2018 I-Codes necessitates changing from the 2007 to the 2014 TPI, and involves significant plating enhancements. However, changing from 2015 to the 2018 IBC/IRC requires no change in TPI, since TPI 2014 is still in effect. Previous revisions were 2002 and 2007.
- NDS, the National Design Specification for Wood Construction, specifies the design properties and methods pertinent to wood. There are no significant changes in allowable lumber stresses since Southern Pine was (significantly) downgraded in June 2013. NDS was revised in 2001, 2005, 2012, 2015, and will be in 2018.
- IBC, the International Building Code, relies on the above 3 design standards for truss design requirements, and is mainly concerned with the design of the overall structure. However, it can significantly impact truss usage, as it did in 2015, by requiring a ceiling to be installed with floor trusses but not with solid joists. I-Codes are revised every three years.
To be competitive requires knowing loading requirements of each jurisdiction served, and their planned adoption of new codes. Every truss job has a specific destination, and, fortunately, design schemes for each jurisdiction can be set up in truss design software.
Our industry associations, SBCA and TPI, are both in the forefront of the code change process, minimizing the impact on component manufacturers, and keeping us up-to-date on pending changes. Soon they will begin advocating and assessing changes submitted for the 2021 I-Codes. Happy New Year!