Ice dam risk in Storm Lake, IA
Ice dams in Storm Lake, IA: how often
27.7 dam days a winter
High risk. On an ordinary house in Storm Lake, conditions for an ice dam come on about 27.7 days in a normal winter, mostly in January and February.
Storm Lake averages 35 inches of snow a year and about 77 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 Storm Lake
| Attic | Dam days | Risk |
|---|---|---|
| Air-sealed and well insulated | 12.1 | Moderate |
| Typical, some insulation, not air-sealed | 27.7 | High |
| Older or poorly insulated, warm attic | 47.4 | Severe |
Sealing and insulating a typical attic takes out about 15.7 days a winter here. It drops the risk from high to moderate. An older house with a warm attic should expect closer to 47.4 days.
Preventing ice dams on a Storm Lake 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.
Storm Lake winter, month by month
| Month | Snow (in) | Days on ground | Dam days |
|---|---|---|---|
| January | 8.0 | 22.7 | 9.5 |
| February | 6.9 | 19.9 | 7.5 |
| March | 6.5 | 9.9 | 2.5 |
| April | 2.3 | 1.2 | 0.1 |
| May | 0.3 | 0.0 | 0.0 |
| October | 0.7 | 0.3 | 0.0 |
| November | 3.8 | 5.8 | 1.4 |
| December | 6.7 | 17.6 | 6.7 |
Storm Lake next to nearby towns
Storm Lake ranks 2 of 41 Iowa cities here for ice-dam days, behind Mason City at 28.7 days.
- Spencer, IA 35 mi, 27.3 days
- Carroll, IA 43 mi, 19.1 days
- Le Mars, IA 51 mi, 24.4 days
- Fort Dodge, IA 53 mi, 24.4 days
- Sioux City, IA 62 mi, 19.2 days
Where these numbers come from
NOAA 1991–2020 climate normals from Sioux Rapids, 17.4 miles from Storm Lake. 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.