Ice dam risk in Watertown, SD
Will your roof get ice dams in Watertown, SD?
35.4 dam days a winter
Severe risk. On an ordinary house in Watertown, conditions for an ice dam come on about 35.4 days in a normal winter, mostly in January and December.
Watertown averages 41 inches of snow a year and about 93 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 | 13.7 | Moderate |
| Typical, some insulation, not air-sealed | 35.4 | Severe |
| Older or poorly insulated, warm attic | 62.6 | Severe |
Sealing and insulating a typical attic takes out about 21.7 days a winter here. It drops the risk from severe to moderate. An older house with a warm attic should expect closer to 62.6 days.
What to do about ice dams in Watertown
- 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 | 6.7 | 25.8 | 11.4 |
| February | 8.9 | 21.4 | 8.7 |
| March | 5.4 | 14.5 | 4.3 |
| April | 5.2 | 3.7 | 0.5 |
| May | 0.1 | 0.0 | 0.0 |
| October | 1.4 | 1.1 | 0.1 |
| November | 4.5 | 4.8 | 1.4 |
| December | 8.9 | 21.5 | 8.9 |
Watertown next to nearby towns
Watertown ranks 1 of 14 South Dakota cities here for ice-dam days, the worst in the state.
- Brookings, SD 46 mi, 31.5 days
- Huron, SD 64 mi, 26.4 days
- Marshall, MN 74 mi, 29.3 days
- Aberdeen, SD 75 mi, 30.2 days
- Mitchell, SD 93 mi, 26.7 days
Where these numbers come from
NOAA 1991–2020 climate normals from Watertown Regional Airport, 0.5 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.