Ice dam risk in DeKalb, IL
Ice dams in DeKalb, IL: how often
19.6 dam days a winter
High risk. On an ordinary house in DeKalb, conditions for an ice dam come on about 19.6 days in a normal winter, mostly in January and February.
DeKalb averages 33 inches of snow a year and about 57 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 DeKalb
| Attic | Dam days | Risk |
|---|---|---|
| Air-sealed and well insulated | 8.7 | Moderate |
| Typical, some insulation, not air-sealed | 19.6 | High |
| Older or poorly insulated, warm attic | 33.4 | High |
Sealing and insulating a typical attic takes out about 11.0 days a winter here. It drops the risk from high to moderate. An older house with a warm attic should expect closer to 33.4 days.
Preventing ice dams on a DeKalb 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.
- 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.
DeKalb winter, month by month
| Month | Snow (in) | Days on ground | Dam days |
|---|---|---|---|
| January | 10.2 | 21.0 | 8.5 |
| February | 8.7 | 15.0 | 5.3 |
| March | 4.4 | 6.2 | 1.4 |
| April | 1.3 | 0.6 | 0.0 |
| October | 0.1 | 0.0 | 0.0 |
| November | 1.8 | 2.0 | 0.4 |
| December | 6.6 | 12.2 | 4.1 |
DeKalb next to nearby towns
DeKalb ranks 13 of 225 Illinois cities here for ice-dam days, behind Arlington Heights at 21.5 days.
- Sycamore, IL 6 mi, 19.6 days
- Campton Hills, IL 17 mi, 14.7 days
- Pingree Grove, IL 20 mi, 14.7 days
- Plano, IL 20 mi, 13.4 days
- Geneva, IL 22 mi, 13.4 days
Where these numbers come from
NOAA 1991–2020 climate normals from De Kalb, 1.4 miles from DeKalb. 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.