Ice dam risk in Carroll, IA
How often ice dams form in Carroll
19.1 dam days a winter
High risk. On an ordinary house in Carroll, conditions for an ice dam come on about 19.1 days in a normal winter, mostly in January and February.
Carroll averages 35 inches of snow a year and about 56 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 Carroll
| Attic | Dam days | Risk |
|---|---|---|
| Air-sealed and well insulated | 8.6 | Moderate |
| Typical, some insulation, not air-sealed | 19.1 | High |
| Older or poorly insulated, warm attic | 32.2 | High |
Sealing and insulating a typical attic takes out about 10.5 days a winter here. It drops the risk from high to moderate. An older house with a warm attic should expect closer to 32.2 days.
Preventing ice dams on a Carroll 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.
Carroll winter, month by month
| Month | Snow (in) | Days on ground | Dam days |
|---|---|---|---|
| January | 8.1 | 17.4 | 6.9 |
| February | 9.2 | 15.9 | 5.8 |
| March | 4.7 | 7.1 | 1.6 |
| April | 1.6 | 0.8 | 0.1 |
| May | 0.1 | 0.0 | 0.0 |
| October | 0.5 | 0.2 | 0.0 |
| November | 2.4 | 3.0 | 0.7 |
| December | 7.9 | 11.1 | 4.0 |
Carroll next to nearby towns
Carroll ranks 15 of 41 Iowa cities here for ice-dam days, behind Mason City at 28.7 days.
- Storm Lake, IA 43 mi, 27.7 days
- Fort Dodge, IA 46 mi, 24.4 days
- Boone, IA 51 mi, 21.8 days
- Waukee, IA 60 mi, 16.1 days
- Grimes, IA 61 mi, 17.8 days
Where these numbers come from
NOAA 1991–2020 climate normals from Denison, 23.9 miles from Carroll. 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.