Tennessee

Statewide summary — confirm with your building department before designing

Snow load audit, August 2026. No statewide ground snow load could be confirmed for Tennessee and both bounds are left NULL. The adopted residential code is the 2018 IRC, taken up by the State Fire Marshal's Office under Tenn. Comp. R. & Regs. 0780-02-23 effective July 16, 2020, and the Fire Marshal's currently adopted codes page confirms that the 2018 IRC is still the residential edition in force alongside the 2021 IBC effective April 17, 2025. Rule 0780-02-23-.02 adopts the 2018 IRC by reference subject to ten enumerated exceptions, and all ten were read: sprinklers made non mandatory, the electrical chapters replaced, smoke alarm power given a new exception, a run of energy code substitutions and two log wall footnotes, and exactly one climatic item, which is seismic rather than snow. That item is government authored text and reads: "Figure R301.2(2) Seismic Design Categories is deleted and replaced with Figure R301.2(2) Seismic Design Categories Site Class D from 2015 IRC." The word snow does not appear anywhere in the 14 page rule, which has a complete text layer. Tennessee therefore publishes no ground snow load and leaves Table R301.2(1) to be completed by the local building official. What was searched for and not found: any snow provision in the adopted rule; a State Fire Marshal climatic and geographic design criteria publication; and any state level snow map or design criteria dataset on tn.gov. The stored ground snow load of 10 psf matches the values adopted by Knox, Blount, Maury and Campbell counties, but those are county figures rather than a state assignment, and 10 psf plainly understates the Great Smoky Mountains, where no Tennessee authority assigns any number at all. That gap, not a low number, is the honest state of the record. None of the four existing values was changed by this pass. Frost depth of 18 inches still exceeds every adopted Tennessee county figure found, which run 10 to 12 inches, and it is left alone because it errs toward over building rather than under building. Seismic design category D, corrected in the earlier audit, remains the West Tennessee governing case. irc_edition corrected 2021 -> 2018: Tennessee State Fire Marshal's Office adopts the 2018 IRC under Tenn. Comp. R. & Regs. 0780-02-23, effective 2020-07-16. The 2021 edition applies to the IBC and related codes effective 2025-04-17, not to the IRC. Memphis and Shelby County separately enforce the 2021 IRC by Joint Ordinance No. 569. Source: https://www.tn.gov/content/dam/tn/commerce/documents/fire_prevention/posts/sfmo-code-adoption-and-history.pdf Seismic design category corrected from B to D and termite risk corrected from very heavy to heavy. West Tennessee sits on the New Madrid seismic zone, the highest seismic hazard east of the Rocky Mountains. The USGS ASCE 7-16 design maps service, read at Site Class D and Risk Category II under the IRC single parameter method, returns short period design accelerations of 0.744 g at Memphis, 0.715 g at Bartlett, 0.595 g at Jackson and 0.543 g at Knoxville, all of which fall in category D. A stored value of B would have left roughly 630,000 people in Memphis and the surrounding Shelby County suburbs braced for well under half the force they must actually resist, and it is the single most consequential error found on this row. Tennessee jurisdictions confirm the picture from the other direction: Campbell County adopted D sub zero for LaFollette, Knox County and Blount County both adopted C, and Maury County adopted B and C. Middle and east Tennessee genuinely are lower, at 0.296 g in Nashville, 0.264 g in Murfreesboro and 0.444 g in Chattanooga, so treat D as the West Tennessee governing case rather than a uniform statewide value. The termite change corrects an overstatement: Knox, Blount, Maury and Campbell counties all adopted the moderate to heavy band, which the stored very heavy exceeds; the very heavy band lies further south along the Gulf. Two other stored values look wrong in the safe direction and were deliberately left alone. Frost depth of 18 inches exceeds every adopted Tennessee figure found, which run 10 inches in Maury, Blount and Campbell counties and 12 inches in Knox County, so it over builds rather than under builds. Ground snow load of 10 psf matches all four of those counties but understates the Great Smoky Mountains. Wind speed of 105 mph sits between the ASCE 7-16 contours and is below the ultimate equivalent of the 90 mph nominal speeds those counties adopted from the older map, and is flagged here rather than changed because the project has not settled whether to round up to the next contour. Confirm your own lot with the local building official. Sources: https://earthquake.usgs.gov/ws/building-codes/, https://www.knoxcounty.org/codes/pdfs/IRC_ammendments.pdf and https://www.lafollettetn.gov/uploads/CODES/CODES_FORM_2021/Building_Construction_Lafollette_Design_Criteria.pdf