Ice dam risk in Andover, MN
How often ice dams form in Andover
39.9 dam days a winter
Severe risk. On an ordinary house in Andover, conditions for an ice dam come on about 39.9 days in a normal winter, mostly in January and February.
Andover averages 44 inches of snow a year and about 106 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 Andover
| Attic | Dam days | Risk |
|---|---|---|
| Air-sealed and well insulated | 15.4 | High |
| Typical, some insulation, not air-sealed | 39.9 | Severe |
| Older or poorly insulated, warm attic | 70.4 | Severe |
Sealing and insulating a typical attic takes out about 24.4 days a winter here. It drops the risk from severe to high. An older house with a warm attic should expect closer to 70.4 days.
Preventing ice dams on a Andover 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 440 kWh a winter in Andover, roughly $75 at 17 cents a kWh.
Which to spend on first: air sealing or heat cable.
Andover winter, month by month
| Month | Snow (in) | Days on ground | Dam days |
|---|---|---|---|
| January | 5.1 | 29.8 | 13.2 |
| February | 9.6 | 24.8 | 10.2 |
| March | 6.3 | 16.6 | 4.4 |
| April | 5.7 | 4.3 | 0.7 |
| October | 0.7 | 0.9 | 0.1 |
| November | 4.3 | 6.1 | 1.5 |
| December | 12.4 | 23.4 | 9.7 |
Andover next to nearby towns
Andover ranks 18 of 103 Minnesota cities here for ice-dam days, behind Hermantown at 52.9 days.
- Anoka, MN 4 mi, 39.9 days
- Coon Rapids, MN 5 mi, 39.9 days
- Ramsey, MN 6 mi, 40.1 days
- Champlin, MN 6 mi, 39.9 days
- Ham Lake, MN 7 mi, 39.9 days
Where these numbers come from
NOAA 1991–2020 climate normals from Andover 1N, 2.2 miles from Andover. 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.