Ice dam risk in Bemidji, MN
How often ice dams form in Bemidji
51.3 dam days a winter
Severe risk. On an ordinary house in Bemidji, conditions for an ice dam come on about 51.3 days in a normal winter, mostly in January and February.
Bemidji averages 49 inches of snow a year and about 131 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 Bemidji
| Attic | Dam days | Risk |
|---|---|---|
| Air-sealed and well insulated | 18.6 | High |
| Typical, some insulation, not air-sealed | 51.3 | Severe |
| Older or poorly insulated, warm attic | 92.3 | Severe |
Sealing and insulating a typical attic takes out about 32.8 days a winter here. It drops the risk from severe to high. An older house with a warm attic should expect closer to 92.3 days.
Preventing ice dams on a Bemidji 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.
- Heat cable is worth pricing here even on a sealed house, along the eave and in the gutters and downspouts it drains into.
Running 60 feet of 5 W/ft cable whenever snow lies below freezing would use about 590 kWh a winter in Bemidji, roughly $100 at 17 cents a kWh.
Which to spend on first: air sealing or heat cable.
Bemidji winter, month by month
| Month | Snow (in) | Days on ground | Dam days |
|---|---|---|---|
| January | 9.1 | 31.0 | 14.5 |
| February | 9.3 | 28.2 | 12.2 |
| March | 6.2 | 24.2 | 7.6 |
| April | 5.6 | 7.5 | 1.4 |
| October | 1.4 | 1.0 | 0.1 |
| November | 5.8 | 12.4 | 4.0 |
| December | 11.5 | 26.2 | 11.6 |
Bemidji next to nearby towns
Bemidji ranks 3 of 103 Minnesota cities here for ice-dam days, behind Hermantown at 52.9 days.
- Detroit Lakes, MN 65 mi, 46.7 days
- Grand Rapids, MN 65 mi, 49.9 days
- Brainerd, MN 85 mi, 46.1 days
- Hibbing, MN 91 mi, 49.9 days
- Moorhead, MN 97 mi, 43.6 days
Where these numbers come from
NOAA 1991–2020 climate normals from Cass Lake, 14.4 miles from Bemidji. 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.