Ice dam risk in Onalaska, WI
Will your roof get ice dams in Onalaska, WI?
26.8 dam days a winter
High risk. On an ordinary house in Onalaska, conditions for an ice dam come on about 26.8 days in a normal winter, mostly in January and February.
Onalaska averages 46 inches of snow a year and about 79 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 Onalaska
| Attic | Dam days | Risk |
|---|---|---|
| Air-sealed and well insulated | 11.8 | Moderate |
| Typical, some insulation, not air-sealed | 26.8 | High |
| Older or poorly insulated, warm attic | 45.6 | Severe |
Sealing and insulating a typical attic takes out about 15.0 days a winter here. It drops the risk from high to moderate. An older house with a warm attic should expect closer to 45.6 days.
Preventing ice dams on a Onalaska 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.
Onalaska winter, month by month
| Month | Snow (in) | Days on ground | Dam days |
|---|---|---|---|
| January | 11.8 | 23.9 | 9.6 |
| February | 9.7 | 21.5 | 7.8 |
| March | 7.3 | 10.6 | 2.4 |
| April | 2.9 | 1.4 | 0.1 |
| October | 0.3 | 0.1 | 0.0 |
| November | 3.4 | 3.5 | 0.7 |
| December | 10.9 | 17.7 | 6.2 |
Onalaska next to nearby towns
Onalaska ranks 38 of 98 Wisconsin cities here for ice-dam days, behind Wausau at 41.6 days.
- La Crosse, WI 5 mi, 32.8 days
- Holmen, WI 6 mi, 26.8 days
- Winona, MN 26 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 Municipal Airport, 2.5 miles from Onalaska. 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.