Ice dam risk in Cedar Rapids, IA
How often ice dams form in Cedar Rapids
18.4 dam days a winter
High risk. On an ordinary house in Cedar Rapids, conditions for an ice dam come on about 18.4 days in a normal winter, mostly in January and February.
Cedar Rapids averages 34 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 Cedar Rapids
| Attic | Dam days | Risk |
|---|---|---|
| Air-sealed and well insulated | 8.7 | Moderate |
| Typical, some insulation, not air-sealed | 18.4 | High |
| Older or poorly insulated, warm attic | 30.5 | High |
Sealing and insulating a typical attic takes out about 9.7 days a winter here. It drops the risk from high to moderate. An older house with a warm attic should expect closer to 30.5 days.
Preventing ice dams on a Cedar Rapids 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.
Cedar Rapids winter, month by month
| Month | Snow (in) | Days on ground | Dam days |
|---|---|---|---|
| January | 8.7 | 20.1 | 7.8 |
| February | 8.3 | 16.0 | 5.2 |
| March | 4.0 | 6.1 | 1.2 |
| April | 1.5 | 0.4 | 0.0 |
| October | 0.6 | 0.1 | 0.0 |
| November | 2.2 | 1.4 | 0.2 |
| December | 9.0 | 12.2 | 4.0 |
Cedar Rapids next to nearby towns
Cedar Rapids ranks 16 of 41 Iowa cities here for ice-dam days, behind Mason City at 28.7 days.
- Marion, IA 7 mi, 18.4 days
- North Liberty, IA 16 mi, 14.9 days
- Coralville, IA 19 mi, 14.9 days
- Iowa City, IA 23 mi, 14.9 days
- Muscatine, IA 49 mi, 12.0 days
Where these numbers come from
NOAA 1991–2020 climate normals from Cedar Rapids #1, 7.5 miles from Cedar Rapids. 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.