Ice dam risk in Ottawa, IL
How often ice dams form in Ottawa
12.3 dam days a winter
Moderate risk. On an ordinary house in Ottawa, conditions for an ice dam come on about 12.3 days in a normal winter, mostly in January and February.
Ottawa averages 25 inches of snow a year and about 39 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 Ottawa
| Attic | Dam days | Risk |
|---|---|---|
| Air-sealed and well insulated | 6.3 | Moderate |
| Typical, some insulation, not air-sealed | 12.3 | Moderate |
| Older or poorly insulated, warm attic | 19.8 | High |
Sealing and insulating a typical attic takes out about 6.0 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 19.8 days.
What to do about ice dams in Ottawa
- 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.
Ottawa winter, month by month
| Month | Snow (in) | Days on ground | Dam days |
|---|---|---|---|
| January | 8.4 | 15.0 | 5.3 |
| February | 7.3 | 10.5 | 3.4 |
| March | 2.9 | 3.6 | 0.8 |
| April | 0.3 | 0.2 | 0.0 |
| November | 0.8 | 0.7 | 0.1 |
| December | 5.3 | 8.7 | 2.7 |
Ottawa next to nearby towns
Ottawa ranks 146 of 225 Illinois cities here for ice-dam days, behind Arlington Heights at 21.5 days.
- Streator, IL 16 mi, 8.9 days
- Morris, IL 21 mi, 11.4 days
- Plano, IL 27 mi, 13.4 days
- Minooka, IL 29 mi, 8.8 days
- Channahon, IL 29 mi, 11.3 days
Where these numbers come from
NOAA 1991–2020 climate normals from Marseilles Lock/Dam, 4.0 miles from Ottawa. 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.