Ice dam risk in Watertown, WI
Will your roof get ice dams in Watertown, WI?
22.3 dam days a winter
High risk. On an ordinary house in Watertown, conditions for an ice dam come on about 22.3 days in a normal winter, mostly in January and February.
Watertown averages 37 inches of snow a year and about 63 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 Watertown
| Attic | Dam days | Risk |
|---|---|---|
| Air-sealed and well insulated | 9.4 | Moderate |
| Typical, some insulation, not air-sealed | 22.3 | High |
| Older or poorly insulated, warm attic | 38.4 | Severe |
Sealing and insulating a typical attic takes out about 12.9 days a winter here. It drops the risk from high to moderate. An older house with a warm attic should expect closer to 38.4 days.
Preventing ice dams on a Watertown 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.
Watertown winter, month by month
| Month | Snow (in) | Days on ground | Dam days |
|---|---|---|---|
| January | 11.0 | 20.8 | 8.6 |
| February | 9.7 | 18.8 | 7.0 |
| March | 4.4 | 7.3 | 1.8 |
| April | 1.6 | 0.9 | 0.1 |
| May | 0.1 | 0.0 | 0.0 |
| October | 0.3 | 0.2 | 0.0 |
| November | 1.4 | 2.4 | 0.5 |
| December | 8.5 | 12.2 | 4.3 |
Watertown next to nearby towns
Watertown ranks 60 of 98 Wisconsin cities here for ice-dam days, behind Wausau at 41.6 days.
- Oconomowoc, WI 13 mi, 22.2 days
- Fort Atkinson, WI 19 mi, 22.2 days
- Hartford, WI 20 mi, 26.7 days
- Beaver Dam, WI 20 mi, 26.8 days
- Hartland, WI 21 mi, 21.4 days
Where these numbers come from
NOAA 1991–2020 climate normals from Watertown Wwtp, 1.1 miles from Watertown. 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.