Ice dam risk in Dixon, IL
Ice dams in Dixon, IL: how often
16.4 dam days a winter
High risk. On an ordinary house in Dixon, conditions for an ice dam come on about 16.4 days in a normal winter, mostly in January and February.
Dixon averages 31 inches of snow a year and about 49 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 Dixon
| Attic | Dam days | Risk |
|---|---|---|
| Air-sealed and well insulated | 7.7 | Moderate |
| Typical, some insulation, not air-sealed | 16.4 | High |
| Older or poorly insulated, warm attic | 27.3 | High |
Sealing and insulating a typical attic takes out about 8.7 days a winter here. It drops the risk from high to moderate. An older house with a warm attic should expect closer to 27.3 days.
Preventing ice dams on a Dixon 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.
- At the next reroof, ask for ice-and-water membrane under the shingles from the eave to at least 24 inches inside the wall line. It does not stop a dam; it stops the leak when one forms.
Which to spend on first: air sealing or heat cable.
Dixon winter, month by month
| Month | Snow (in) | Days on ground | Dam days |
|---|---|---|---|
| January | 13.0 | 20.0 | 7.7 |
| February | 5.7 | 13.4 | 4.4 |
| March | 4.5 | 3.8 | 0.8 |
| April | 0.6 | 0.3 | 0.0 |
| November | 1.8 | 1.5 | 0.3 |
| December | 5.6 | 10.4 | 3.3 |
Dixon next to nearby towns
Dixon ranks 42 of 225 Illinois cities here for ice-dam days, behind Arlington Heights at 21.5 days.
- Sterling, IL 12 mi, 16.4 days
- Freeport, IL 32 mi, 19.2 days
- Rockford, IL 36 mi, 18.2 days
- DeKalb, IL 38 mi, 19.6 days
- Clinton, IA 39 mi, 16.6 days
Where these numbers come from
NOAA 1991–2020 climate normals from Dixon 1W, 1.9 miles from Dixon. 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.