Twenty pounds per square foot of ground snow load is the number Detroit’s building permits are built around, and it’s tempting to treat that as the answer to how much snow a Michigan roof can carry. It isn’t. The code converts that ground figure down for an ordinary sloped roof, then pushes parts of it back up wherever snow drifts against a wall or a dormer. If you’re worried about a specific roof, the concrete first step is to pull the truss drawings or call the local building department rather than compare snow depth to a psf number.
What is the ground snow load in Michigan?
The design ground snow load at Detroit, Michigan is 20 psf under ASCE 7-16, the edition that IRC/IBC 2021 makes applicable in most states. That is the number a permit application, a plan review and a truss drawing all start from, but it is a ground figure, not a roof figure. The code runs it through exposure, thermal and slope factors before anything reaches a rafter, and for an ordinary heated sloped house roof the result lands around 14 psf of roof snow load, not 20.
A few jurisdictions are beginning to look at ASCE 7-22, which maps the same point at 37 psf. That is not more snow falling on Detroit and it is not a sign that a roof built to the 7-16 number is undersized. ASCE 7-22 works on a strength-level basis with a 1.0 load factor, while 7-16 is a nominal value used with a 1.6 factor, so the two numbers aren’t measuring the same thing. The figure that governs an actual Michigan permit today is the 7-16 value.
Detroit is the reference point for this figure, and Michigan’s terrain does the rest of the work in changing it. Coastal states run into the same problem for a different reason: readers dealing with this question along the Atlantic can see how a different reference city changes the numbers on Massachusetts’s roof snow load and wind rules. A local building department or a licensed engineer applies the map value to the specific site, and that is the only way to know what a given roof was actually designed for.
How much snow can a roof hold in Michigan?
There’s no single number here, because the load on a real roof depends on slope, drift and what the snow itself has turned into. Start from the same ground figure: Detroit’s design ground snow load of 20 psf under ASCE 7-16 gives roughly 14 psf on an ordinary sloped, heated roof, and a steeper roof carries even less because snow doesn’t sit as long or as deep on a steep pitch.
Where drift changes the math
That 14 psf figure assumes snow spread evenly across the roof, which is rarely what happens. Wind moves snow off a high roof and piles it against a wall, below a dormer, or into a valley between two roof planes, and a lower roof next to a taller one can pick up several times the base load in that drift zone alone. Drift is where roofs actually fail, not under an even blanket of snow, and it’s also the load a homeowner is least likely to notice, because it sits in one corner rather than across the whole field of view.
Depth is not weight
The other variable is what the snow has become. Snow weight depends on how settled or wet it is, so the same depth can weigh much more after it settles or gets rained on. An ice layer on top adds more still. That’s why a foot of snow that fell during a January cold snap is a very different load than a foot that sat through a March thaw and refroze, even though a tape measure would call them the same.
A few signs suggest a roof is carrying more than it should, regardless of what the design number says:
- Interior doors that suddenly stick or won’t latch
- New cracks in ceiling drywall or at wall-ceiling joints
- A visible sag along the ridge line or a roof plane that looks wavy from the yard
- Creaking or popping sounds from the attic framing under load
If any of that shows up, the safe response is to reduce the load from the ground with a roof rake, not to climb onto a loaded roof and shovel it, which adds a person’s weight to a structure that may already be stressed. For anything beyond raking reachable snow, a call to the local building department or a licensed engineer is the next step, not a guess.
What wind speed must a roof withstand in Michigan?
The basic design wind speed at Detroit, Michigan is 108 mph under ASCE 7-16, and that number needs its basis stated before it means anything. It’s a 3-second gust measured at 33 feet in open, Exposure C terrain, for Risk Category II buildings, which covers ordinary houses. It is not a sustained wind, not a hurricane’s headline number, and not what a weather forecast means when it gives a wind speed. Comparing it directly to a tropical storm’s reported wind speed will make the code look weak when it isn’t measuring the same thing at all.
ASCE 7-22 maps the same point at 108 mph as well, so the newer edition and the one currently governing Michigan permits agree rather than diverge. That doesn’t change what the number does. It still sets the pressures a builder designs the roof assembly to resist, not a promise about the worst gust the site will ever see.
What the number actually governs
A 108 mph design wind speed feeds into the shingle wind rating a roofer specifies, the nailing pattern used to fasten them, how the sheathing is fastened to the rafters or trusses, and the uplift connections, straps or clips, tying the roof structure down to the walls. Edges, rakes and ridges fail first in a wind event because that’s where uplift pressure concentrates, which is why fastening requirements are tighter at the perimeter of a roof than elsewhere on the same slope.
The reference point for the 108 mph figure is Detroit, and Michigan’s design wind speed is not uniform across the state. Mapped wind values can differ from place to place, so a homeowner shouldn’t assume the Detroit figure applies without checking the map for their own location with the local building department. A state without Michigan’s lake-effect snow load still has its own wind and ice-barrier rules to work through, as the Tennessee page on Tennessee’s roof snow load and wind rules shows for a very different climate.
Does Michigan require an ice barrier under the shingles?
An ice barrier is one layer in the broader roofing assembly, a self-adhering waterproof membrane installed under the shingles. It isn’t there to stop snow. It’s there to stop meltwater that backs up behind an ice dam from finding a gap in the underlayment and reaching the roof deck, and from there, the ceiling below.
Why ice dams form here
An ice dam has nothing to do with how much snow fell and everything to do with heat. Warm air leaking from the living space into the attic melts the underside of the snow layer on the roof. That meltwater runs down the roof deck until it reaches the cold overhang past the exterior wall, where there’s no heat loss underneath to keep it liquid, and it refreezes there. Snow keeps landing on top, meltwater keeps running down, and the ice at the eave keeps growing until it’s damming water that has nowhere to go but sideways, under the shingles.
Detroit’s mean minimum temperature in the coldest month sits at 19.2°F, according to NOAA’s 1991-2020 climate normals, meaning the average night in the coldest stretch of a Michigan winter doesn’t climb out of the high teens. Combined with a design ground snow load of 20 psf under ASCE 7-16, that’s a real setup for the freeze-thaw cycle at the eave that causes ice damming, not a marginal one.
Michigan’s residential construction is governed by the 2015 Michigan Residential Code, part of the Michigan Administrative Code, based on the 2015 International Residential Code and enforced statewide by the Michigan Department of Licensing and Regulatory Affairs, Bureau of Construction Codes. As a uniform state code, municipalities can’t weaken it. A planned update to the 2021 IRC was scheduled for August 2025 but is currently suspended by a Michigan Court of Claims order, so the 2015 code remains in force. The 2015 IRC’s model text requires an ice barrier membrane at the eaves in climates with a history of ice forming and causing water backup. A local building department can confirm exactly how far up the roof the membrane needs to run on a specific project, since that detail depends on the roof’s slope and the wall line beneath it.
The membrane only protects the deck. It doesn’t stop the dam from forming in the first place, and a roof with a well-installed ice barrier sitting over a poorly insulated, poorly air-sealed attic will still grow ice at the eaves every winter. Air sealing the attic floor and bringing insulation up to level are what actually stop the heat loss. A reader treating the membrane as the whole fix has bought protection against the symptom, not the cause.
What roofing material suits Michigan best?
The honest answer starts from the loads: a 20 psf ground snow load at Detroit under ASCE 7-16 that converts to roughly 14 psf on an ordinary sloped roof, a 108 mph design wind speed, and a climate where, of Michigan’s 83 counties, 44 fall in IECC climate zone 6A, 37 in zone 5A and 2 in zone 7 under the 2021 IECC’s county tables. No single material is best across all three. Each one changes what the roof does with the load rather than eliminating it.
| Material | Wind performance | Snow behavior | Added dead load |
|---|---|---|---|
| Architectural asphalt shingles | Rated by wind class, performance depends on matching the nailing pattern to the rating | Holds snow on the roof rather than shedding it | Low, adds little to the structural load already carried |
| Standing-seam metal | Strong uplift resistance when panels and clips are properly fastened | Sheds snow in a slide rather than holding it, sometimes suddenly | Low, similar to shingles |
| Slate or concrete tile | Heavy individual units resist wind uplift well when properly fastened | Holds snow similarly to shingles | Substantial, the tile’s own weight adds to the snow load the structure must carry |
Standing-seam metal is worth a specific caution in a state with this kind of ground snow load, because shedding well is not automatically a good thing. When snow lets go of a smooth metal roof, it doesn’t come off in a slow trickle, it can come off in one slab, and where that slab lands is a design decision, not an accident. A roof plane that discharges over a doorway, a walkway, or a driveway needs a snow guard, a redirected roof line, or a clear drop zone planned before the roof goes on, not after someone gets hit by it.
Slate and concrete tile carry their own weight into the same structural calculation the snow load uses. A roof framed for an asphalt shingle load isn’t automatically adequate for a tile roof, because the tile itself might weigh substantially more than the shingles it replaces. That’s a structural question for whoever designed or is re-evaluating the framing, not a matter of picking a tile that looks right.
Fastening decides as much as material
Where wind governs, the fastening and the underlayment matter more than which material sits on top. A shingle rated for a high wind speed performs only as well as the nailing pattern it’s actually installed with, and a metal panel rated for strong uplift resistance is only as good as the clips holding it down. Michigan’s design wind speed of 108 mph at Detroit under ASCE 7-16 is a real number for a truss drawing and a roofing spec, and it says nothing about the roof’s outcome if the installation doesn’t match the rating on the package.