Ice dam risk in Coralville, IA
Will your roof get ice dams in Coralville, IA?
14.9 dam days a winter
Moderate risk. On an ordinary house in Coralville, conditions for an ice dam come on about 14.9 days in a normal winter, mostly in January and February.
Coralville averages 28 inches of snow a year and about 48 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 Coralville
| Attic | Dam days | Risk |
|---|---|---|
| Air-sealed and well insulated | 7.7 | Moderate |
| Typical, some insulation, not air-sealed | 14.9 | Moderate |
| Older or poorly insulated, warm attic | 23.8 | High |
Sealing and insulating a typical attic takes out about 7.1 days a winter here. It does not move the risk band, but it shortens every dam. An older house with a warm attic should expect closer to 23.8 days.
Preventing ice dams on a Coralville 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.
Which to spend on first: air sealing or heat cable.
Coralville winter, month by month
| Month | Snow (in) | Days on ground | Dam days |
|---|---|---|---|
| January | 7.6 | 17.9 | 6.5 |
| February | 7.5 | 13.1 | 4.0 |
| March | 3.2 | 3.8 | 0.7 |
| April | 0.5 | 0.4 | 0.0 |
| October | 0.4 | 0.1 | 0.0 |
| November | 1.1 | 1.9 | 0.3 |
| December | 7.2 | 11.1 | 3.3 |
Coralville next to nearby towns
Coralville ranks 33 of 41 Iowa cities here for ice-dam days, behind Mason City at 28.7 days.
- North Liberty, IA 3 mi, 14.9 days
- Iowa City, IA 5 mi, 14.9 days
- Cedar Rapids, IA 19 mi, 18.4 days
- Marion, IA 24 mi, 18.4 days
- Muscatine, IA 33 mi, 12.0 days
Where these numbers come from
NOAA 1991–2020 climate normals from Iowa City, 7.8 miles from Coralville. 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.