Ice dam risk in Le Mars, IA
Will your roof get ice dams in Le Mars, IA?
24.4 dam days a winter
High risk. On an ordinary house in Le Mars, conditions for an ice dam come on about 24.4 days in a normal winter, mostly in January and December.
Le Mars averages 31 inches of snow a year and about 70 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 Le Mars
| Attic | Dam days | Risk |
|---|---|---|
| Air-sealed and well insulated | 11.4 | Moderate |
| Typical, some insulation, not air-sealed | 24.4 | High |
| Older or poorly insulated, warm attic | 40.6 | Severe |
Sealing and insulating a typical attic takes out about 13.0 days a winter here. It drops the risk from high to moderate. An older house with a warm attic should expect closer to 40.6 days.
What to do about ice dams in Le Mars
- 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.
Le Mars winter, month by month
| Month | Snow (in) | Days on ground | Dam days |
|---|---|---|---|
| January | 7.8 | 21.2 | 8.6 |
| February | 7.5 | 16.6 | 6.1 |
| March | 4.6 | 8.5 | 2.1 |
| April | 1.9 | 1.1 | 0.1 |
| May | 0.1 | 0.0 | 0.0 |
| October | 0.4 | 0.2 | 0.0 |
| November | 2.6 | 4.6 | 1.1 |
| December | 6.0 | 17.3 | 6.3 |
Le Mars next to nearby towns
Le Mars ranks 5 of 41 Iowa cities here for ice-dam days, behind Mason City at 28.7 days.
- Sioux City, IA 23 mi, 19.2 days
- South Sioux City, NE 25 mi, 19.2 days
- Vermillion, SD 38 mi, 23.8 days
- Storm Lake, IA 51 mi, 27.7 days
- Harrisburg, SD 53 mi, 26.7 days
Where these numbers come from
NOAA 1991–2020 climate normals from Le Mars, 1.4 miles from Le Mars. 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.
- Snow-on-the-ground counts come from a second, nearby station, because the closest one does not record them.