Ice dam risk in Cary, IL
Ice dams in Cary, IL: how often
18.8 dam days a winter
High risk. On an ordinary house in Cary, conditions for an ice dam come on about 18.8 days in a normal winter, mostly in January and February.
Cary averages 35 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 Cary
| Attic | Dam days | Risk |
|---|---|---|
| Air-sealed and well insulated | 8.4 | Moderate |
| Typical, some insulation, not air-sealed | 18.8 | High |
| Older or poorly insulated, warm attic | 31.8 | High |
Sealing and insulating a typical attic takes out about 10.4 days a winter here. It drops the risk from high to moderate. An older house with a warm attic should expect closer to 31.8 days.
What to do about ice dams in Cary
- 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.
Cary winter, month by month
| Month | Snow (in) | Days on ground | Dam days |
|---|---|---|---|
| January | 11.0 | 20.0 | 7.8 |
| February | 8.9 | 16.2 | 5.7 |
| March | 3.9 | 6.3 | 1.4 |
| April | 1.0 | 0.6 | 0.0 |
| October | 0.1 | 0.0 | 0.0 |
| November | 1.4 | 1.5 | 0.3 |
| December | 8.2 | 10.6 | 3.5 |
Cary next to nearby towns
Cary ranks 25 of 225 Illinois cities here for ice-dam days, behind Arlington Heights at 21.5 days.
- Lake in the Hills, IL 4 mi, 16.8 days
- Crystal Lake, IL 5 mi, 16.8 days
- Algonquin, IL 5 mi, 14.7 days
- Carpentersville, IL 7 mi, 14.7 days
- Wauconda, IL 7 mi, 18.6 days
Where these numbers come from
NOAA 1991–2020 climate normals from Mc Henry -Wg Stratton L&d, 6.7 miles from Cary. 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.