Ice dam risk in Marshfield, WI
How often ice dams form in Marshfield
37.5 dam days a winter
Severe risk. On an ordinary house in Marshfield, conditions for an ice dam come on about 37.5 days in a normal winter, mostly in January and February.
Marshfield averages 57 inches of snow a year and about 100 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 Marshfield
| Attic | Dam days | Risk |
|---|---|---|
| Air-sealed and well insulated | 15.0 | Moderate |
| Typical, some insulation, not air-sealed | 37.5 | Severe |
| Older or poorly insulated, warm attic | 65.6 | Severe |
Sealing and insulating a typical attic takes out about 22.5 days a winter here. It drops the risk from severe to moderate. An older house with a warm attic should expect closer to 65.6 days.
Preventing ice dams on a Marshfield 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.
Marshfield winter, month by month
| Month | Snow (in) | Days on ground | Dam days |
|---|---|---|---|
| January | 12.4 | 26.6 | 11.8 |
| February | 11.7 | 27.3 | 10.9 |
| March | 8.8 | 17.7 | 4.8 |
| April | 5.1 | 3.3 | 0.4 |
| May | 0.1 | 0.0 | 0.0 |
| October | 0.7 | 0.3 | 0.0 |
| November | 4.9 | 4.0 | 1.0 |
| December | 13.4 | 21.1 | 8.4 |
Marshfield next to nearby towns
Marshfield ranks 10 of 98 Wisconsin cities here for ice-dam days, behind Wausau at 41.6 days.
- Wisconsin Rapids, WI 25 mi, 37.8 days
- Stevens Point, WI 32 mi, 37.8 days
- Wausau, WI 33 mi, 41.6 days
- Plover, WI 34 mi, 37.8 days
- Weston, WI 34 mi, 41.6 days
Where these numbers come from
NOAA 1991–2020 climate normals from Marshfield Exp Farm, 2.4 miles from Marshfield. 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.