Ice dam risk in North Chicago, IL
How often ice dams form in North Chicago
18.6 dam days a winter
High risk. On an ordinary house in North Chicago, conditions for an ice dam come on about 18.6 days in a normal winter, mostly in January and February.
North Chicago averages 43 inches of snow a year and about 55 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 North Chicago
| Attic | Dam days | Risk |
|---|---|---|
| Air-sealed and well insulated | 8.5 | Moderate |
| Typical, some insulation, not air-sealed | 18.6 | High |
| Older or poorly insulated, warm attic | 31.2 | High |
Sealing and insulating a typical attic takes out about 10.1 days a winter here. It drops the risk from high to moderate. An older house with a warm attic should expect closer to 31.2 days.
What to do about ice dams in North Chicago
- 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.
North Chicago winter, month by month
| Month | Snow (in) | Days on ground | Dam days |
|---|---|---|---|
| January | 11.0 | 18.3 | 7.0 |
| February | 12.8 | 16.4 | 5.9 |
| March | 5.3 | 6.3 | 1.4 |
| April | 1.8 | 0.8 | 0.1 |
| November | 2.5 | 1.7 | 0.3 |
| December | 9.7 | 11.9 | 3.9 |
North Chicago next to nearby towns
North Chicago ranks 28 of 225 Illinois cities here for ice-dam days, behind Arlington Heights at 21.5 days.
- Waukegan, IL 4 mi, 20.1 days
- Gurnee, IL 5 mi, 20.1 days
- Lake Forest, IL 6 mi, 16.1 days
- Libertyville, IL 6 mi, 18.6 days
- Vernon Hills, IL 8 mi, 18.6 days
Where these numbers come from
NOAA 1991–2020 climate normals from Mundelein 4 WSW, 11.9 miles from North Chicago. 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.