Ice dam risk in Morris, IL
Ice dams in Morris, IL: how often
11.4 dam days a winter
Moderate risk. On an ordinary house in Morris, conditions for an ice dam come on about 11.4 days in a normal winter, mostly in January and February.
Morris averages 25 inches of snow a year and about 37 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 Morris
| Attic | Dam days | Risk |
|---|---|---|
| Air-sealed and well insulated | 5.7 | Moderate |
| Typical, some insulation, not air-sealed | 11.4 | Moderate |
| Older or poorly insulated, warm attic | 18.5 | High |
Sealing and insulating a typical attic takes out about 5.7 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 18.5 days.
Preventing ice dams on a Morris 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.
Morris winter, month by month
| Month | Snow (in) | Days on ground | Dam days |
|---|---|---|---|
| January | 7.4 | 14.4 | 5.1 |
| February | 7.5 | 10.7 | 3.4 |
| March | 2.9 | 3.2 | 0.6 |
| April | 0.5 | 0.3 | 0.0 |
| November | 1.1 | 1.1 | 0.2 |
| December | 5.3 | 7.1 | 2.1 |
Morris next to nearby towns
Morris ranks 169 of 225 Illinois cities here for ice-dam days, behind Arlington Heights at 21.5 days.
- Channahon, IL 9 mi, 11.3 days
- Minooka, IL 9 mi, 8.8 days
- Shorewood, IL 14 mi, 8.8 days
- Joliet, IL 17 mi, 8.8 days
- Plainfield, IL 19 mi, 12.2 days
Where these numbers come from
NOAA 1991–2020 climate normals from Morris 1 NW, 0.8 miles from Morris. 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.