Ice dam risk in Fairmont, MN
Will your roof get ice dams in Fairmont, MN?
30.3 dam days a winter
High risk. On an ordinary house in Fairmont, conditions for an ice dam come on about 30.3 days in a normal winter, mostly in January and December.
Fairmont averages 40 inches of snow a year and about 82 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 Fairmont
| Attic | Dam days | Risk |
|---|---|---|
| Air-sealed and well insulated | 12.4 | Moderate |
| Typical, some insulation, not air-sealed | 30.3 | High |
| Older or poorly insulated, warm attic | 52.7 | Severe |
Sealing and insulating a typical attic takes out about 17.9 days a winter here. It drops the risk from high to moderate. An older house with a warm attic should expect closer to 52.7 days.
What to do about ice dams in Fairmont
- 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.
Fairmont winter, month by month
| Month | Snow (in) | Days on ground | Dam days |
|---|---|---|---|
| January | 10.9 | 22.8 | 9.9 |
| February | 8.5 | 20.9 | 8.1 |
| March | 4.6 | 9.6 | 2.6 |
| April | 3.6 | 1.4 | 0.1 |
| October | 0.7 | 0.3 | 0.0 |
| November | 3.1 | 5.9 | 1.5 |
| December | 8.3 | 20.6 | 8.0 |
Fairmont next to nearby towns
Fairmont ranks 84 of 103 Minnesota cities here for ice-dam days, behind Hermantown at 52.9 days.
- North Mankato, MN 43 mi, 30.4 days
- Mankato, MN 44 mi, 30.4 days
- New Ulm, MN 46 mi, 30.5 days
- Spencer, IA 49 mi, 27.3 days
- St. Peter, MN 53 mi, 24.7 days
Where these numbers come from
NOAA 1991–2020 climate normals from Swea City 5N, 15.3 miles from Fairmont. 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.