Ice dam risk in Manitowoc, WI
Will your roof get ice dams in Manitowoc, WI?
26.2 dam days a winter
High risk. On an ordinary house in Manitowoc, conditions for an ice dam come on about 26.2 days in a normal winter, mostly in February and January.
Manitowoc averages 35 inches of snow a year and about 78 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 Manitowoc
| Attic | Dam days | Risk |
|---|---|---|
| Air-sealed and well insulated | 11.5 | Moderate |
| Typical, some insulation, not air-sealed | 26.2 | High |
| Older or poorly insulated, warm attic | 44.6 | Severe |
Sealing and insulating a typical attic takes out about 14.7 days a winter here. It drops the risk from high to moderate. An older house with a warm attic should expect closer to 44.6 days.
What to do about ice dams in Manitowoc
- 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.
Manitowoc winter, month by month
| Month | Snow (in) | Days on ground | Dam days |
|---|---|---|---|
| January | 7.8 | 22.9 | 9.2 |
| February | 10.0 | 23.5 | 8.7 |
| March | 3.2 | 13.6 | 3.3 |
| April | 1.4 | 1.5 | 0.1 |
| October | 0.2 | 0.1 | 0.0 |
| November | 0.9 | 2.6 | 0.4 |
| December | 11.1 | 13.4 | 4.4 |
Manitowoc next to nearby towns
Manitowoc ranks 46 of 98 Wisconsin cities here for ice-dam days, behind Wausau at 41.6 days.
- Two Rivers, WI 6 mi, 26.6 days
- Sheboygan, WI 25 mi, 27.5 days
- Bellevue, WI 29 mi, 29.3 days
- De Pere, WI 30 mi, 31.4 days
- Allouez, WI 31 mi, 29.3 days
Where these numbers come from
NOAA 1991–2020 climate normals from Manitowoc, 1.5 miles from Manitowoc. 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.
- Snow-on-the-ground counts come from a second, nearby station, because the closest one does not record them.