Ice dam risk in St. Peter, MN
How often ice dams form in St. Peter
24.7 dam days a winter
High risk. On an ordinary house in St. Peter, conditions for an ice dam come on about 24.7 days in a normal winter, mostly in January and February.
St. Peter averages 38 inches of snow a year and about 65 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 St. Peter
| Attic | Dam days | Risk |
|---|---|---|
| Air-sealed and well insulated | 9.7 | Moderate |
| Typical, some insulation, not air-sealed | 24.7 | High |
| Older or poorly insulated, warm attic | 43.3 | Severe |
Sealing and insulating a typical attic takes out about 14.9 days a winter here. It drops the risk from high to moderate. An older house with a warm attic should expect closer to 43.3 days.
What to do about ice dams in St. Peter
- 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.
St. Peter winter, month by month
| Month | Snow (in) | Days on ground | Dam days |
|---|---|---|---|
| January | 8.8 | 20.9 | 9.1 |
| February | 8.2 | 16.2 | 6.4 |
| March | 4.2 | 10.1 | 2.8 |
| April | 2.7 | 0.9 | 0.1 |
| October | 0.2 | 0.1 | 0.0 |
| November | 3.2 | 2.9 | 0.7 |
| December | 10.6 | 14.1 | 5.5 |
St. Peter next to nearby towns
St. Peter ranks 86 of 103 Minnesota cities here for ice-dam days, behind Hermantown at 52.9 days.
- North Mankato, MN 11 mi, 30.4 days
- Mankato, MN 11 mi, 30.4 days
- New Ulm, MN 25 mi, 30.5 days
- Faribault, MN 34 mi, 33.6 days
- Waconia, MN 36 mi, 32.4 days
Where these numbers come from
NOAA 1991–2020 climate normals from St Peter, 0.5 miles from St. Peter. 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.