Ice dam risk in Yankton, SD
Will your roof get ice dams in Yankton, SD?
18.8 dam days a winter
High risk. On an ordinary house in Yankton, conditions for an ice dam come on about 18.8 days in a normal winter, mostly in January and February.
Yankton averages 38 inches of snow a year and about 58 days with snow on the ground. Most of it comes and goes within a few days. 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 Yankton
| Attic | Dam days | Risk |
|---|---|---|
| Air-sealed and well insulated | 9.8 | Moderate |
| Typical, some insulation, not air-sealed | 18.8 | High |
| Older or poorly insulated, warm attic | 30.1 | High |
Sealing and insulating a typical attic takes out about 9.0 days a winter here. It drops the risk from high to moderate. An older house with a warm attic should expect closer to 30.1 days.
Preventing ice dams on a Yankton 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.
Yankton winter, month by month
| Month | Snow (in) | Days on ground | Dam days |
|---|---|---|---|
| January | 6.7 | 17.6 | 6.7 |
| February | 8.5 | 13.4 | 4.6 |
| March | 4.7 | 7.4 | 1.7 |
| April | 3.7 | 1.5 | 0.2 |
| May | 0.2 | 0.0 | 0.0 |
| October | 0.8 | 0.4 | 0.0 |
| November | 5.9 | 4.4 | 1.0 |
| December | 7.6 | 12.8 | 4.4 |
Yankton next to nearby towns
Yankton ranks 11 of 14 South Dakota cities here for ice-dam days, behind Watertown at 35.4 days.
- Vermillion, SD 25 mi, 23.8 days
- Harrisburg, SD 51 mi, 26.7 days
- Sioux Falls, SD 56 mi, 25.5 days
- Sioux City, IA 58 mi, 19.2 days
- South Sioux City, NE 58 mi, 19.2 days
Where these numbers come from
NOAA 1991–2020 climate normals from Yankton 2 E, 1.7 miles from Yankton. 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.