Ice dam risk in Macomb, IL
How often ice dams form in Macomb
10.6 dam days a winter
Moderate risk. On an ordinary house in Macomb, conditions for an ice dam come on about 10.6 days in a normal winter, mostly in January and February.
Macomb averages 21 inches of snow a year and about 36 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 Macomb
| Attic | Dam days | Risk |
|---|---|---|
| Air-sealed and well insulated | 5.9 | Moderate |
| Typical, some insulation, not air-sealed | 10.6 | Moderate |
| Older or poorly insulated, warm attic | 16.6 | High |
Sealing and insulating a typical attic takes out about 4.8 days a winter here. It does not move the risk band, but it shortens every dam. An older house with a warm attic should expect closer to 16.6 days.
Preventing ice dams on a Macomb 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.
Which to spend on first: air sealing or heat cable.
Macomb winter, month by month
| Month | Snow (in) | Days on ground | Dam days |
|---|---|---|---|
| January | 5.7 | 14.2 | 4.7 |
| February | 6.0 | 9.6 | 3.0 |
| March | 2.5 | 2.8 | 0.5 |
| April | 1.0 | 0.2 | 0.0 |
| November | 1.1 | 0.8 | 0.1 |
| December | 5.0 | 8.3 | 2.3 |
Macomb next to nearby towns
Macomb ranks 174 of 225 Illinois cities here for ice-dam days, behind Arlington Heights at 21.5 days.
- Burlington, IA 33 mi, 10.0 days
- Canton, IL 35 mi, 10.4 days
- Galesburg, IL 37 mi, 13.8 days
- Quincy, IL 52 mi, 6.7 days
- Pekin, IL 56 mi, 10.3 days
Where these numbers come from
NOAA 1991–2020 climate normals from Prairie City 2S, 14.2 miles from Macomb. 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.