Ice dam risk in La Crosse, WI
How often ice dams form in La Crosse
32.8 dam days a winter
High risk. On an ordinary house in La Crosse, conditions for an ice dam come on about 32.8 days in a normal winter, mostly in February and January.
La Crosse averages 54 inches of snow a year and about 88 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 La Crosse
| Attic | Dam days | Risk |
|---|---|---|
| Air-sealed and well insulated | 12.2 | Moderate |
| Typical, some insulation, not air-sealed | 32.8 | High |
| Older or poorly insulated, warm attic | 58.6 | Severe |
Sealing and insulating a typical attic takes out about 20.6 days a winter here. It drops the risk from high to moderate. An older house with a warm attic should expect closer to 58.6 days.
Preventing ice dams on a La Crosse 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.
Which to spend on first: air sealing or heat cable.
La Crosse winter, month by month
| Month | Snow (in) | Days on ground | Dam days |
|---|---|---|---|
| January | 10.5 | 23.2 | 10.1 |
| February | 12.4 | 24.6 | 10.1 |
| March | 8.3 | 13.8 | 3.5 |
| April | 4.5 | 2.4 | 0.2 |
| October | 0.5 | 0.2 | 0.0 |
| November | 3.5 | 3.7 | 0.8 |
| December | 14.5 | 20.3 | 8.1 |
La Crosse next to nearby towns
La Crosse ranks 13 of 98 Wisconsin cities here for ice-dam days, behind Wausau at 41.6 days.
- Onalaska, WI 5 mi, 26.8 days
- Holmen, WI 10 mi, 26.8 days
- Winona, MN 27 mi, 30.7 days
- Rochester, MN 64 mi, 33.3 days
- Reedsburg, WI 65 mi, 25.3 days
Where these numbers come from
NOAA 1991–2020 climate normals from La Crosse Wfo, 1.7 miles from La Crosse. 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.