Ice dam risk in Freeport, IL
How often ice dams form in Freeport
19.2 dam days a winter
High risk. On an ordinary house in Freeport, conditions for an ice dam come on about 19.2 days in a normal winter, mostly in January and February.
Freeport averages 35 inches of snow a year and about 56 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 Freeport
| Attic | Dam days | Risk |
|---|---|---|
| Air-sealed and well insulated | 8.8 | Moderate |
| Typical, some insulation, not air-sealed | 19.2 | High |
| Older or poorly insulated, warm attic | 32.2 | High |
Sealing and insulating a typical attic takes out about 10.4 days a winter here. It drops the risk from high to moderate. An older house with a warm attic should expect closer to 32.2 days.
Preventing ice dams on a Freeport 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.
Freeport winter, month by month
| Month | Snow (in) | Days on ground | Dam days |
|---|---|---|---|
| January | 9.7 | 20.3 | 8.2 |
| February | 8.5 | 15.1 | 5.2 |
| March | 3.8 | 5.1 | 1.2 |
| April | 0.8 | 0.6 | 0.0 |
| October | 0.2 | 0.1 | 0.0 |
| November | 2.6 | 2.4 | 0.5 |
| December | 8.9 | 12.1 | 4.1 |
Freeport next to nearby towns
Freeport ranks 15 of 225 Illinois cities here for ice-dam days, behind Arlington Heights at 21.5 days.
- Monroe, WI 22 mi, 24.4 days
- Rockford, IL 29 mi, 18.2 days
- Machesney Park, IL 32 mi, 20.5 days
- Dixon, IL 32 mi, 16.4 days
- Loves Park, IL 33 mi, 18.2 days
Where these numbers come from
NOAA 1991–2020 climate normals from Freeport Waste Wtp, 1.7 miles from Freeport. 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.