Ice dam risk in Pontiac, IL
Will your roof get ice dams in Pontiac, IL?
9.6 dam days a winter
Moderate risk. On an ordinary house in Pontiac, conditions for an ice dam come on about 9.6 days in a normal winter, mostly in January and February.
Pontiac averages 25 inches of snow a year and about 31 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 Pontiac
| Attic | Dam days | Risk |
|---|---|---|
| Air-sealed and well insulated | 4.8 | Low |
| Typical, some insulation, not air-sealed | 9.6 | Moderate |
| Older or poorly insulated, warm attic | 15.7 | High |
Sealing and insulating a typical attic takes out about 4.8 days a winter here. It drops the risk from moderate to low. An older house with a warm attic should expect closer to 15.7 days.
Preventing ice dams on a Pontiac 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.
Which to spend on first: air sealing or heat cable.
Pontiac winter, month by month
| Month | Snow (in) | Days on ground | Dam days |
|---|---|---|---|
| January | 6.7 | 12.7 | 4.4 |
| February | 8.0 | 9.4 | 2.9 |
| March | 3.4 | 1.8 | 0.3 |
| April | 0.6 | 0.2 | 0.0 |
| November | 0.7 | 0.4 | 0.1 |
| December | 5.7 | 6.4 | 1.9 |
Pontiac next to nearby towns
Pontiac ranks 182 of 225 Illinois cities here for ice-dam days, behind Arlington Heights at 21.5 days.
- Streator, IL 19 mi, 8.9 days
- Normal, IL 31 mi, 9.8 days
- Bloomington, IL 33 mi, 9.8 days
- Ottawa, IL 33 mi, 12.3 days
- Morris, IL 36 mi, 11.4 days
Where these numbers come from
NOAA 1991–2020 climate normals from Pontiac, 0.8 miles from Pontiac. 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.