Iowa

Statewide summary — confirm with your building department before designing

No value on this row was changed by this audit. IRC Table R301.2 is filled in by the local jurisdiction, not by the state, so treat every figure here as a summary and not as your lot requirement. Seismic design category A is defensible statewide: under ASCE 7-16 at Site Class D and Risk Category II, all of Iowa bands to A on short-period spectral response, from Sioux City through Des Moines and Davenport to Keokuk, and the full determination puts most of the state at B, a distinction that does not change residential requirements. Ground snow load 30 psf is the value for northwest and northeast Iowa including Sioux City and Dubuque; Des Moines is 25 psf and Davenport 20 psf, so the stored figure is conservative rather than wrong. Ultimate design wind speed 105 mph is the ASCE 7-16 interior base contour at Risk Category II, but every Iowa site checked interpolates above it, from about 108 mph at Davenport and Dubuque to about 110 at Des Moines and 112 at Sioux City; 110 mph is the reading to stand behind and 105 should not be used in western Iowa. Frost depth 42 inches is set locally in Iowa and was not verified against any government source. The termite designation slight encodes the IRC slight-to-moderate band, which fits northern Iowa; southern Iowa is likely in the moderate-to-heavy band, and neither was confirmed against an Iowa authority. The winter design temperature is ASHRAE 99 percent data, is not published by any Iowa authority, and is unverified. Snow load audit, August 2026. Iowa publishes no statewide ground snow load, and that absence is proven from the adopted instrument rather than assumed. The state building code now lives at 481 IAC chapter 301, moved there from 661 IAC chapter 301 by editorial change effective 11/26/25, and rule 481-301.8 adopts the 2024 International Residential Code with a short list of amendments. Subrule 301.8(3) is the entire answer on design criteria and, being state-authored rule text, can be quoted: "Note: The values for Table R301.2 are determined by the location of the project and referenced footnotes from Table R301.2." The word snow does not appear anywhere in the chapter, and there is no Iowa county table, map or appendix of ground snow loads. Both range columns are therefore left null rather than invented. Scope matters when reading anything on this row as an Iowa requirement. Under Iowa Code 103A.10 the state building code is mandatory only for buildings owned by the state or a state agency, for newly constructed buildings paid for in whole or in part with state-appropriated money, in each city over fifteen thousand people that has not adopted a local code substantially in accord with a nationally recognized building code, and in any governmental subdivision whose governing body has enacted an ordinance accepting it. Everywhere else the local ordinance governs and the building official fills in Table R301.2. None of the four existing values was changed. Seismic design category A was re-confirmed against the USGS ASCE 7-16 design maps service at Site Class D and Risk Category II, which returns short-period design accelerations of about 0.087 g at Sioux City, 0.066 g at Des Moines and 0.118 g at Keokuk; all three fall in category A on the single short-period parameter the IRC uses, while the full two-parameter determination puts Des Moines and Keokuk in B. Ground snow load 30 psf, wind speed 105 mph and frost depth 42 inches remain unconfirmed against any Iowa government source, because no such source exists to confirm them against.