Ice dam risk in Fort Atkinson, WI
Will your roof get ice dams in Fort Atkinson, WI?
22.2 dam days a winter
High risk. On an ordinary house in Fort Atkinson, conditions for an ice dam come on about 22.2 days in a normal winter, mostly in January and February.
Fort Atkinson averages 36 inches of snow a year and about 65 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 Fort Atkinson
| Attic | Dam days | Risk |
|---|---|---|
| Air-sealed and well insulated | 9.9 | Moderate |
| Typical, some insulation, not air-sealed | 22.2 | High |
| Older or poorly insulated, warm attic | 37.4 | Severe |
Sealing and insulating a typical attic takes out about 12.2 days a winter here. It drops the risk from high to moderate. An older house with a warm attic should expect closer to 37.4 days.
What to do about ice dams in Fort Atkinson
- 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.
Fort Atkinson winter, month by month
| Month | Snow (in) | Days on ground | Dam days |
|---|---|---|---|
| January | 10.7 | 21.5 | 8.6 |
| February | 9.4 | 18.5 | 6.6 |
| March | 4.0 | 7.4 | 1.8 |
| April | 1.2 | 0.7 | 0.1 |
| May | 0.2 | 0.1 | 0.0 |
| October | 0.1 | 0.1 | 0.0 |
| November | 2.1 | 2.8 | 0.6 |
| December | 8.7 | 13.4 | 4.5 |
Fort Atkinson next to nearby towns
Fort Atkinson ranks 66 of 98 Wisconsin cities here for ice-dam days, behind Wausau at 41.6 days.
- Whitewater, WI 8 mi, 21.9 days
- Janesville, WI 19 mi, 20.5 days
- Stoughton, WI 19 mi, 23.9 days
- Watertown, WI 19 mi, 22.3 days
- Oconomowoc, WI 22 mi, 22.2 days
Where these numbers come from
NOAA 1991–2020 climate normals from Ft Atkinson Wwtp, 1.5 miles from Fort Atkinson. 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.