Ice dam risk in Mahomet, IL
Will your roof get ice dams in Mahomet, IL?
8.8 dam days a winter
Moderate risk. On an ordinary house in Mahomet, conditions for an ice dam come on about 8.8 days in a normal winter, mostly in January and February.
Mahomet averages 21 inches of snow a year and about 30 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 Mahomet
| Attic | Dam days | Risk |
|---|---|---|
| Air-sealed and well insulated | 4.7 | Low |
| Typical, some insulation, not air-sealed | 8.8 | Moderate |
| Older or poorly insulated, warm attic | 13.9 | Moderate |
Sealing and insulating a typical attic takes out about 4.1 days a winter here. It drops the risk from moderate to low. An older house with a warm attic should expect closer to 13.9 days.
What to do about ice dams in Mahomet
- 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.
Mahomet winter, month by month
| Month | Snow (in) | Days on ground | Dam days |
|---|---|---|---|
| January | 6.5 | 12.2 | 4.1 |
| February | 5.8 | 8.6 | 2.5 |
| March | 2.5 | 2.3 | 0.4 |
| April | 0.3 | 0.1 | 0.0 |
| November | 0.9 | 0.9 | 0.1 |
| December | 4.8 | 5.8 | 1.6 |
Mahomet next to nearby towns
Mahomet ranks 191 of 225 Illinois cities here for ice-dam days, behind Arlington Heights at 21.5 days.
- Champaign, IL 8 mi, 8.8 days
- Urbana, IL 12 mi, 8.8 days
- Rantoul, IL 15 mi, 9.6 days
- Bloomington, IL 36 mi, 9.8 days
- Decatur, IL 37 mi, 6.9 days
Where these numbers come from
NOAA 1991–2020 climate normals from Champaign 3S, 10.8 miles from Mahomet. 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.