Michigan

Statewide summary — confirm with your building department before designing

No value on this row was changed by this audit, but Michigan publishes its own binding table and you should use it rather than this row. The Michigan Residential Code amends Table R301.2(1) and adds Table R301.2(5), which assigns a ground snow load to every county and to many individual cities, villages and townships. Ground snow load 30 psf is untenable as a single Michigan number: the state table runs from 20 psf in Wayne, Monroe and Lenawee counties to 90 and 100 psf in Keweenaw County. Wayne County, which contains Detroit, is 20 psf and Oakland and Macomb are 25; Kent County around Grand Rapids is 35; Traverse City is 60; Marquette, Alger, Baraga, Luce, Chippewa and Ontonagon are 70; Houghton is 80. The stored 30 psf over-states the Detroit metropolitan area by half and under-states the Upper Peninsula by a factor of three, so look your jurisdiction up in Table R301.2(5) before designing anything. Frost line depth 42 inches is correct and is fixed statewide by the Michigan Residential Code amendment to Table R301.2(1), subject to modification under Section R403.1.4. Seismic design category A is correct and holds throughout Michigan, which has very low mapped seismic hazard. Ultimate design wind speed 105 mph is the ASCE 7-16 interior base contour at Risk Category II and Michigan site values run about 104 to 108 mph; the Michigan code leaves this cell for the local jurisdiction to fill in from the basic wind speed map. The termite designation slight encodes the IRC slight-to-moderate band, which fits the Lower Peninsula; the northern Upper Peninsula is likely in the none-to-slight band. The Michigan code carries a footnote here rather than a designation, so this was not confirmed. The winter design temperature is ASHRAE data; the Michigan code refers to an appendix of the Michigan plumbing code rather than fixing a value here, so the stored figure is unverified.