Ice dam risk in Duluth, MN
Will your roof get ice dams in Duluth, MN?
38.4 dam days a winter
Severe risk. On an ordinary house in Duluth, conditions for an ice dam come on about 38.4 days in a normal winter, mostly in January and February.
Duluth averages 56 inches of snow a year and about 101 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 Duluth
| Attic | Dam days | Risk |
|---|---|---|
| Air-sealed and well insulated | 14.3 | Moderate |
| Typical, some insulation, not air-sealed | 38.4 | Severe |
| Older or poorly insulated, warm attic | 68.5 | Severe |
Sealing and insulating a typical attic takes out about 24.1 days a winter here. It drops the risk from severe to moderate. An older house with a warm attic should expect closer to 68.5 days.
What to do about ice dams in Duluth
- 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.
Duluth winter, month by month
| Month | Snow (in) | Days on ground | Dam days |
|---|---|---|---|
| January | 14.5 | 26.1 | 11.7 |
| February | 12.4 | 25.7 | 10.7 |
| March | 9.1 | 18.9 | 5.8 |
| April | 1.7 | 3.8 | 0.5 |
| October | 0.2 | 0.1 | 0.0 |
| November | 5.8 | 6.6 | 1.7 |
| December | 12.3 | 20.2 | 8.1 |
Duluth next to nearby towns
Duluth ranks 26 of 103 Minnesota cities here for ice-dam days, behind Hermantown at 52.9 days.
- Hermantown, MN 5 mi, 52.9 days
- Superior, WI 6 mi, 38.4 days
- Cloquet, MN 18 mi, 52.2 days
- Hibbing, MN 57 mi, 49.9 days
- Grand Rapids, MN 73 mi, 49.9 days
Where these numbers come from
NOAA 1991–2020 climate normals from Superior, 4.4 miles from Duluth. 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.