Ice dam risk in Willmar, MN
Ice dams in Willmar, MN: how often
37.6 dam days a winter
Severe risk. On an ordinary house in Willmar, conditions for an ice dam come on about 37.6 days in a normal winter, mostly in January and February.
Willmar averages 46 inches of snow a year and about 96 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 Willmar
| Attic | Dam days | Risk |
|---|---|---|
| Air-sealed and well insulated | 13.8 | Moderate |
| Typical, some insulation, not air-sealed | 37.6 | Severe |
| Older or poorly insulated, warm attic | 67.4 | Severe |
Sealing and insulating a typical attic takes out about 23.8 days a winter here. It drops the risk from severe to moderate. An older house with a warm attic should expect closer to 67.4 days.
What to do about ice dams in Willmar
- 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.
Willmar winter, month by month
| Month | Snow (in) | Days on ground | Dam days |
|---|---|---|---|
| January | 9.2 | 26.3 | 12.0 |
| February | 7.8 | 24.6 | 10.2 |
| March | 6.9 | 16.1 | 4.6 |
| April | 3.8 | 1.8 | 0.2 |
| October | 0.5 | 0.1 | 0.0 |
| November | 7.8 | 7.3 | 2.1 |
| December | 10.1 | 20.2 | 8.5 |
Willmar next to nearby towns
Willmar ranks 27 of 103 Minnesota cities here for ice-dam days, behind Hermantown at 52.9 days.
- Hutchinson, MN 37 mi, 35.5 days
- St. Cloud, MN 51 mi, 38.6 days
- Sartell, MN 54 mi, 39.1 days
- Alexandria, MN 54 mi, 40.8 days
- Sauk Rapids, MN 55 mi, 38.6 days
Where these numbers come from
NOAA 1991–2020 climate normals from Willmar Wwtp, 1.4 miles from Willmar. 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.
- Snow-on-the-ground counts come from a second, nearby station, because the closest one does not record them.