Ice dam risk in Marshall, MN
Ice dams in Marshall, MN: how often
29.3 dam days a winter
High risk. On an ordinary house in Marshall, conditions for an ice dam come on about 29.3 days in a normal winter, mostly in January and February.
Marshall averages 44 inches of snow a year and about 81 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 Marshall
| Attic | Dam days | Risk |
|---|---|---|
| Air-sealed and well insulated | 12.0 | Moderate |
| Typical, some insulation, not air-sealed | 29.3 | High |
| Older or poorly insulated, warm attic | 50.8 | Severe |
Sealing and insulating a typical attic takes out about 17.3 days a winter here. It drops the risk from high to moderate. An older house with a warm attic should expect closer to 50.8 days.
What to do about ice dams in Marshall
- 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.
Marshall winter, month by month
| Month | Snow (in) | Days on ground | Dam days |
|---|---|---|---|
| January | 6.6 | 23.6 | 9.9 |
| February | 8.1 | 19.5 | 7.6 |
| March | 7.6 | 12.8 | 3.4 |
| April | 4.9 | 2.1 | 0.2 |
| May | 0.1 | 0.0 | 0.0 |
| October | 0.8 | 0.5 | 0.0 |
| November | 5.3 | 4.4 | 1.1 |
| December | 10.1 | 18.0 | 7.0 |
Marshall next to nearby towns
Marshall ranks 85 of 103 Minnesota cities here for ice-dam days, behind Hermantown at 52.9 days.
- Brookings, SD 50 mi, 31.5 days
- Worthington, MN 57 mi, 34.3 days
- Willmar, MN 59 mi, 37.6 days
- New Ulm, MN 66 mi, 30.5 days
- Brandon, SD 71 mi, 25.5 days
Where these numbers come from
NOAA 1991–2020 climate normals from Marshall, 1.6 miles from Marshall. 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.