Ice dam risk in Prior Lake, MN
Ice dams in Prior Lake, MN: how often
33.9 dam days a winter
High risk. On an ordinary house in Prior Lake, conditions for an ice dam come on about 33.9 days in a normal winter, mostly in January and February.
Prior Lake averages 55 inches of snow a year and about 91 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 Prior Lake
| Attic | Dam days | Risk |
|---|---|---|
| Air-sealed and well insulated | 12.8 | Moderate |
| Typical, some insulation, not air-sealed | 33.9 | High |
| Older or poorly insulated, warm attic | 60.2 | Severe |
Sealing and insulating a typical attic takes out about 21.0 days a winter here. It drops the risk from high to moderate. An older house with a warm attic should expect closer to 60.2 days.
What to do about ice dams in Prior Lake
- 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.
Prior Lake winter, month by month
| Month | Snow (in) | Days on ground | Dam days |
|---|---|---|---|
| January | 10.0 | 26.0 | 11.5 |
| February | 11.2 | 22.8 | 9.2 |
| March | 9.1 | 15.0 | 4.0 |
| April | 5.4 | 2.5 | 0.2 |
| October | 0.6 | 0.3 | 0.0 |
| November | 5.1 | 5.1 | 1.3 |
| December | 13.3 | 19.1 | 7.7 |
Prior Lake next to nearby towns
Prior Lake ranks 53 of 103 Minnesota cities here for ice-dam days, behind Hermantown at 52.9 days.
- Shakopee, MN 4 mi, 33.9 days
- Savage, MN 4 mi, 32.4 days
- Burnsville, MN 8 mi, 32.6 days
- Eden Prairie, MN 9 mi, 33.9 days
- Bloomington, MN 9 mi, 32.4 days
Where these numbers come from
NOAA 1991–2020 climate normals from Chanhassen Wsfo, 10.5 miles from Prior Lake. 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.