Ice dam risk in Chatham, IL
Ice dams in Chatham, IL: how often
7.1 dam days a winter
Moderate risk. On an ordinary house in Chatham, conditions for an ice dam come on about 7.1 days in a normal winter, mostly in January and February.
Chatham averages 22 inches of snow a year and about 27 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 Chatham
| Attic | Dam days | Risk |
|---|---|---|
| Air-sealed and well insulated | 4.1 | Low |
| Typical, some insulation, not air-sealed | 7.1 | Moderate |
| Older or poorly insulated, warm attic | 10.9 | Moderate |
Sealing and insulating a typical attic takes out about 3.0 days a winter here. It drops the risk from moderate to low. An older house with a warm attic should expect closer to 10.9 days.
Preventing ice dams on a Chatham 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.
Chatham winter, month by month
| Month | Snow (in) | Days on ground | Dam days |
|---|---|---|---|
| January | 6.7 | 10.6 | 3.3 |
| February | 6.1 | 7.2 | 1.9 |
| March | 3.1 | 2.0 | 0.3 |
| April | 0.3 | 0.1 | 0.0 |
| October | 0.1 | 0.0 | 0.0 |
| November | 1.2 | 0.9 | 0.1 |
| December | 4.3 | 6.0 | 1.5 |
Chatham next to nearby towns
Chatham ranks 195 of 225 Illinois cities here for ice-dam days, behind Arlington Heights at 21.5 days.
- Springfield, IL 8 mi, 7.1 days
- Taylorville, IL 22 mi, 6.3 days
- Jacksonville, IL 29 mi, 6.3 days
- Lincoln, IL 37 mi, 7.4 days
- Decatur, IL 42 mi, 6.9 days
Where these numbers come from
NOAA 1991–2020 climate normals from Springfield Abraham Lincoln Ca, 11.8 miles from Chatham. 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.