Ice dam risk in Oshkosh, WI
Ice dams in Oshkosh, WI: how often
27.2 dam days a winter
High risk. On an ordinary house in Oshkosh, conditions for an ice dam come on about 27.2 days in a normal winter, mostly in February and January.
Oshkosh averages 39 inches of snow a year and about 77 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 Oshkosh
| Attic | Dam days | Risk |
|---|---|---|
| Air-sealed and well insulated | 11.3 | Moderate |
| Typical, some insulation, not air-sealed | 27.2 | High |
| Older or poorly insulated, warm attic | 47.1 | Severe |
Sealing and insulating a typical attic takes out about 15.9 days a winter here. It drops the risk from high to moderate. An older house with a warm attic should expect closer to 47.1 days.
Preventing ice dams on a Oshkosh 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.
Oshkosh winter, month by month
| Month | Snow (in) | Days on ground | Dam days |
|---|---|---|---|
| January | 9.8 | 22.9 | 9.5 |
| February | 10.1 | 24.3 | 9.2 |
| March | 5.4 | 12.0 | 3.0 |
| April | 1.8 | 1.3 | 0.1 |
| October | 0.3 | 0.1 | 0.0 |
| November | 1.8 | 1.8 | 0.4 |
| December | 10.0 | 14.2 | 5.1 |
Oshkosh next to nearby towns
Oshkosh ranks 37 of 98 Wisconsin cities here for ice-dam days, behind Wausau at 41.6 days.
- Neenah, WI 11 mi, 30.0 days
- Fox Crossing, WI 14 mi, 30.0 days
- Menasha, WI 15 mi, 30.0 days
- Harrison, WI 18 mi, 30.0 days
- Greenville, WI 18 mi, 30.0 days
Where these numbers come from
NOAA 1991–2020 climate normals from Oshkosh, 0.3 miles from Oshkosh. 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.