Ice dam risk in Collinsville, IL
Will your roof get ice dams in Collinsville, IL?
3.6 dam days a winter
Low risk. On an ordinary house in Collinsville, conditions for an ice dam come on about 3.6 days in a normal winter, mostly in January and December.
Collinsville averages 14 inches of snow a year and about 15 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 Collinsville
| Attic | Dam days | Risk |
|---|---|---|
| Air-sealed and well insulated | 2.4 | Low |
| Typical, some insulation, not air-sealed | 3.6 | Low |
| Older or poorly insulated, warm attic | 5.0 | Low |
The attic matters less in Collinsville than in colder towns: there are only 1.2 days a winter between a typical attic and a sealed one.
Preventing ice dams on a Collinsville roof
- Check the gutters before the first snow and clear them, so meltwater has somewhere to go. If you see icicles thicker than a finger along the eave after a storm, that is the early sign to look at the attic.
Snowy places are not always the worst: why snowfall misleads.
Collinsville winter, month by month
| Month | Snow (in) | Days on ground | Dam days |
|---|---|---|---|
| January | 4.9 | 7.2 | 1.9 |
| February | 3.7 | 3.5 | 0.7 |
| March | 1.2 | 0.6 | 0.1 |
| April | 0.3 | 0.1 | 0.0 |
| November | 0.8 | 0.5 | 0.0 |
| December | 2.9 | 3.5 | 0.8 |
Collinsville next to nearby towns
Collinsville ranks 209 of 225 Illinois cities here for ice-dam days, behind Arlington Heights at 21.5 days.
- Fairview Heights, IL 6 mi, 2.5 days
- Glen Carbon, IL 6 mi, 3.6 days
- Troy, IL 7 mi, 2.5 days
- Granite City, IL 7 mi, 3.6 days
- O'Fallon, IL 7 mi, 2.5 days
Where these numbers come from
NOAA 1991–2020 climate normals from Cahokia, 12.6 miles from Collinsville. 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.