Ice dam risk in Normal, IL
Ice dams in Normal, IL: how often
9.8 dam days a winter
Moderate risk. On an ordinary house in Normal, conditions for an ice dam come on about 9.8 days in a normal winter, mostly in January and February.
Normal averages 20 inches of snow a year and about 32 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 Normal
| Attic | Dam days | Risk |
|---|---|---|
| Air-sealed and well insulated | 5.3 | Moderate |
| Typical, some insulation, not air-sealed | 9.8 | Moderate |
| Older or poorly insulated, warm attic | 15.5 | High |
Sealing and insulating a typical attic takes out about 4.5 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 15.5 days.
What to do about ice dams in Normal
- 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.
Normal winter, month by month
| Month | Snow (in) | Days on ground | Dam days |
|---|---|---|---|
| January | 7.5 | 13.9 | 4.8 |
| February | 5.5 | 7.4 | 2.2 |
| March | 2.2 | 2.6 | 0.5 |
| April | 0.5 | 0.2 | 0.0 |
| November | 0.8 | 1.1 | 0.2 |
| December | 3.6 | 7.0 | 2.1 |
Normal next to nearby towns
Normal ranks 180 of 225 Illinois cities here for ice-dam days, behind Arlington Heights at 21.5 days.
- Bloomington, IL 3 mi, 9.8 days
- Morton, IL 26 mi, 12.1 days
- Washington, IL 26 mi, 12.1 days
- East Peoria, IL 31 mi, 10.3 days
- Pontiac, IL 31 mi, 9.6 days
Where these numbers come from
NOAA 1991–2020 climate normals from Normal 4NE, 3.0 miles from Normal. 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.