Ice dam risk in Pierre, SD
Ice dams in Pierre, SD: how often
21.9 dam days a winter
High risk. On an ordinary house in Pierre, conditions for an ice dam come on about 21.9 days in a normal winter, mostly in January and December.
Pierre averages 37 inches of snow a year and about 67 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 Pierre
| Attic | Dam days | Risk |
|---|---|---|
| Air-sealed and well insulated | 11.2 | Moderate |
| Typical, some insulation, not air-sealed | 21.9 | High |
| Older or poorly insulated, warm attic | 35.1 | Severe |
Sealing and insulating a typical attic takes out about 10.6 days a winter here. It drops the risk from high to moderate. An older house with a warm attic should expect closer to 35.1 days.
What to do about ice dams in Pierre
- 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.
Pierre winter, month by month
| Month | Snow (in) | Days on ground | Dam days |
|---|---|---|---|
| January | 5.1 | 20.1 | 7.7 |
| February | 8.0 | 13.4 | 4.7 |
| March | 5.0 | 9.2 | 2.3 |
| April | 5.3 | 2.5 | 0.3 |
| October | 1.3 | 0.8 | 0.1 |
| November | 6.3 | 5.6 | 1.4 |
| December | 6.2 | 15.0 | 5.4 |
Pierre next to nearby towns
Pierre ranks 10 of 14 South Dakota cities here for ice-dam days, behind Watertown at 35.4 days.
- Huron, SD 104 mi, 26.4 days
- Aberdeen, SD 118 mi, 30.2 days
- Mitchell, SD 122 mi, 26.7 days
- Box Elder, SD 138 mi, 13.9 days
- Rapid City, SD 145 mi, 11.8 days
Where these numbers come from
NOAA 1991–2020 climate normals from Pierre Regional Airport, 1.7 miles from Pierre. 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.