Ice dam risk in Machesney Park, IL
Ice dams in Machesney Park, IL: how often
20.5 dam days a winter
High risk. On an ordinary house in Machesney Park, conditions for an ice dam come on about 20.5 days in a normal winter, mostly in January and February.
Machesney Park averages 36 inches of snow a year and about 60 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 Machesney Park
| Attic | Dam days | Risk |
|---|---|---|
| Air-sealed and well insulated | 9.1 | Moderate |
| Typical, some insulation, not air-sealed | 20.5 | High |
| Older or poorly insulated, warm attic | 34.9 | High |
Sealing and insulating a typical attic takes out about 11.5 days a winter here. It drops the risk from high to moderate. An older house with a warm attic should expect closer to 34.9 days.
Preventing ice dams on a Machesney Park 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.
Machesney Park winter, month by month
| Month | Snow (in) | Days on ground | Dam days |
|---|---|---|---|
| January | 9.8 | 20.7 | 8.3 |
| February | 7.3 | 16.9 | 6.0 |
| March | 4.3 | 6.6 | 1.5 |
| April | 1.1 | 0.6 | 0.0 |
| October | 0.2 | 0.1 | 0.0 |
| November | 2.7 | 2.1 | 0.4 |
| December | 10.2 | 12.7 | 4.3 |
Machesney Park next to nearby towns
Machesney Park ranks 5 of 225 Illinois cities here for ice-dam days, behind Arlington Heights at 21.5 days.
- Loves Park, IL 2 mi, 18.2 days
- Roscoe, IL 4 mi, 20.5 days
- Rockford, IL 8 mi, 18.2 days
- Belvidere, IL 10 mi, 18.2 days
- Beloit, WI 11 mi, 20.5 days
Where these numbers come from
NOAA 1991–2020 climate normals from Beloit, 9.4 miles from Machesney Park. 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.