Ice dam risk in Rock Island, IL
Will your roof get ice dams in Rock Island, IL?
14.0 dam days a winter
Moderate risk. On an ordinary house in Rock Island, conditions for an ice dam come on about 14.0 days in a normal winter, mostly in January and February.
Rock Island averages 36 inches of snow a year and about 46 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 Rock Island
| Attic | Dam days | Risk |
|---|---|---|
| Air-sealed and well insulated | 7.2 | Moderate |
| Typical, some insulation, not air-sealed | 14.0 | Moderate |
| Older or poorly insulated, warm attic | 22.6 | High |
Sealing and insulating a typical attic takes out about 6.9 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 22.6 days.
Preventing ice dams on a Rock Island 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.
Rock Island winter, month by month
| Month | Snow (in) | Days on ground | Dam days |
|---|---|---|---|
| January | 10.8 | 15.4 | 5.5 |
| February | 8.6 | 14.5 | 4.5 |
| March | 4.4 | 3.9 | 0.7 |
| April | 1.1 | 0.3 | 0.0 |
| October | 0.3 | 0.1 | 0.0 |
| November | 2.1 | 1.1 | 0.2 |
| December | 8.8 | 10.3 | 3.1 |
Rock Island next to nearby towns
Rock Island ranks 83 of 225 Illinois cities here for ice-dam days, behind Arlington Heights at 21.5 days.
- Moline, IL 5 mi, 15.9 days
- Davenport, IA 6 mi, 14.0 days
- Bettendorf, IA 9 mi, 15.9 days
- East Moline, IL 11 mi, 15.9 days
- Muscatine, IA 25 mi, 12.0 days
Where these numbers come from
NOAA 1991–2020 climate normals from Moline Quad City International Airport, 3.5 miles from Rock Island. 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.