Ice dam risk in Westmont, IL
Ice dams in Westmont, IL: how often
11.6 dam days a winter
Moderate risk. On an ordinary house in Westmont, conditions for an ice dam come on about 11.6 days in a normal winter, mostly in January and February.
Westmont averages 24 inches of snow a year and about 41 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 Westmont
| Attic | Dam days | Risk |
|---|---|---|
| Air-sealed and well insulated | 6.7 | Moderate |
| Typical, some insulation, not air-sealed | 11.6 | Moderate |
| Older or poorly insulated, warm attic | 17.7 | High |
Sealing and insulating a typical attic takes out about 4.9 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 17.7 days.
What to do about ice dams in Westmont
- 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.
Westmont winter, month by month
| Month | Snow (in) | Days on ground | Dam days |
|---|---|---|---|
| January | 9.3 | 17.4 | 5.7 |
| February | 5.1 | 10.6 | 2.8 |
| March | 4.5 | 4.4 | 0.8 |
| April | 0.3 | 0.2 | 0.0 |
| November | 0.9 | 1.2 | 0.2 |
| December | 4.2 | 7.5 | 2.0 |
Westmont next to nearby towns
Westmont ranks 163 of 225 Illinois cities here for ice-dam days, behind Arlington Heights at 21.5 days.
- Hinsdale, IL 2 mi, 11.6 days
- Downers Grove, IL 2 mi, 11.6 days
- Darien, IL 3 mi, 11.6 days
- Western Springs, IL 4 mi, 12.8 days
- Burr Ridge, IL 4 mi, 12.8 days
Where these numbers come from
NOAA 1991–2020 climate normals from Wheaton 3 SE, 5.3 miles from Westmont. 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.