Ice dam risk in Sioux Falls, SD
Will your roof get ice dams in Sioux Falls, SD?
25.5 dam days a winter
High risk. On an ordinary house in Sioux Falls, conditions for an ice dam come on about 25.5 days in a normal winter, mostly in January and December.
Sioux Falls averages 45 inches of snow a year and about 73 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 Sioux Falls
| Attic | Dam days | Risk |
|---|---|---|
| Air-sealed and well insulated | 11.5 | Moderate |
| Typical, some insulation, not air-sealed | 25.5 | High |
| Older or poorly insulated, warm attic | 42.9 | Severe |
Sealing and insulating a typical attic takes out about 13.9 days a winter here. It drops the risk from high to moderate. An older house with a warm attic should expect closer to 42.9 days.
Preventing ice dams on a Sioux Falls 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.
Sioux Falls winter, month by month
| Month | Snow (in) | Days on ground | Dam days |
|---|---|---|---|
| January | 8.0 | 22.3 | 9.1 |
| February | 8.6 | 15.9 | 6.0 |
| March | 7.2 | 10.1 | 2.5 |
| April | 5.1 | 2.3 | 0.3 |
| May | 0.1 | 0.1 | 0.0 |
| October | 1.4 | 0.5 | 0.0 |
| November | 6.2 | 5.3 | 1.4 |
| December | 8.7 | 16.4 | 6.2 |
Sioux Falls next to nearby towns
Sioux Falls ranks 7 of 14 South Dakota cities here for ice-dam days, behind Watertown at 35.4 days.
- Harrisburg, SD 7 mi, 26.7 days
- Brandon, SD 8 mi, 25.5 days
- Brookings, SD 53 mi, 31.5 days
- Vermillion, SD 53 mi, 23.8 days
- Yankton, SD 56 mi, 18.8 days
Where these numbers come from
NOAA 1991–2020 climate normals from Sioux Falls, 3.3 miles from Sioux Falls. 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.