Ice dam risk in St. Michael, MN
How often ice dams form in St. Michael
36.4 dam days a winter
Severe risk. On an ordinary house in St. Michael, conditions for an ice dam come on about 36.4 days in a normal winter, mostly in January and February.
St. Michael averages 40 inches of snow a year and about 95 days with snow on the ground. Snow that lies that long is what turns a little attic heat into a ridge of ice at the eave. The conditions that make a dam need all three at once: snow, cold at the eave and heat above it.
What your attic does to that number in St. Michael
| Attic | Dam days | Risk |
|---|---|---|
| Air-sealed and well insulated | 13.8 | Moderate |
| Typical, some insulation, not air-sealed | 36.4 | Severe |
| Older or poorly insulated, warm attic | 64.7 | Severe |
Sealing and insulating a typical attic takes out about 22.6 days a winter here. It drops the risk from severe to moderate. An older house with a warm attic should expect closer to 64.7 days.
Preventing ice dams on a St. Michael roof
- Air-seal the attic floor: the gaps around the hatch, light fixtures, plumbing stacks and the top plates of interior walls. This is the fix that removes the cause, and it usually costs less than a season of contractor ice removal.
- Rake the bottom three or four feet of roof after any storm that leaves more than about six inches, from the ground with a roof rake.
- At the next reroof, ask for ice-and-water membrane under the shingles from the eave to at least 24 inches inside the wall line. It does not stop a dam; it stops the leak when one forms.
Which to spend on first: air sealing or heat cable.
St. Michael winter, month by month
| Month | Snow (in) | Days on ground | Dam days |
|---|---|---|---|
| January | 7.3 | 26.6 | 12.0 |
| February | 8.0 | 25.2 | 10.2 |
| March | 6.8 | 14.0 | 3.9 |
| April | 2.6 | 1.9 | 0.2 |
| October | 0.2 | 0.2 | 0.0 |
| November | 5.6 | 7.1 | 1.9 |
| December | 9.3 | 19.9 | 8.2 |
St. Michael next to nearby towns
St. Michael ranks 45 of 103 Minnesota cities here for ice-dam days, behind Hermantown at 52.9 days.
- Otsego, MN 6 mi, 36.5 days
- Rogers, MN 6 mi, 36.5 days
- Monticello, MN 8 mi, 36.4 days
- Buffalo, MN 9 mi, 36.4 days
- Big Lake, MN 10 mi, 36.5 days
Where these numbers come from
NOAA 1991–2020 climate normals from Buffalo 2NE, 7.3 miles from St. Michael. A dam day is a day with snow on the roof and freezing at the eave while heat or sun melts the snow above it. This describes a normal winter, not this one.