Ice dam risk in Jacksonville, IL
Will your roof get ice dams in Jacksonville, IL?
6.3 dam days a winter
Moderate risk. On an ordinary house in Jacksonville, conditions for an ice dam come on about 6.3 days in a normal winter, mostly in January and February.
Jacksonville averages 16 inches of snow a year and about 23 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 Jacksonville
| Attic | Dam days | Risk |
|---|---|---|
| Air-sealed and well insulated | 3.9 | Low |
| Typical, some insulation, not air-sealed | 6.3 | Moderate |
| Older or poorly insulated, warm attic | 9.4 | Moderate |
Sealing and insulating a typical attic takes out about 2.5 days a winter here. It drops the risk from moderate to low. An older house with a warm attic should expect closer to 9.4 days.
Preventing ice dams on a Jacksonville 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.
Which to spend on first: air sealing or heat cable.
Jacksonville winter, month by month
| Month | Snow (in) | Days on ground | Dam days |
|---|---|---|---|
| January | 5.1 | 9.5 | 3.1 |
| February | 4.3 | 5.6 | 1.5 |
| March | 2.0 | 2.0 | 0.3 |
| April | 0.3 | 0.1 | 0.0 |
| November | 1.0 | 0.6 | 0.1 |
| December | 3.5 | 4.9 | 1.3 |
Jacksonville next to nearby towns
Jacksonville ranks 199 of 225 Illinois cities here for ice-dam days, behind Arlington Heights at 21.5 days.
- Chatham, IL 29 mi, 7.1 days
- Springfield, IL 32 mi, 7.1 days
- Taylorville, IL 50 mi, 6.3 days
- Godfrey, IL 54 mi, 4.8 days
- Lincoln, IL 54 mi, 7.4 days
Where these numbers come from
NOAA 1991–2020 climate normals from Jacksonville 2E, 1.9 miles from Jacksonville. 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.