Ice dam risk in Washington, IL
Will your roof get ice dams in Washington, IL?
12.1 dam days a winter
Moderate risk. On an ordinary house in Washington, conditions for an ice dam come on about 12.1 days in a normal winter, mostly in January and February.
Washington averages 22 inches of snow a year and about 41 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 Washington
| Attic | Dam days | Risk |
|---|---|---|
| Air-sealed and well insulated | 6.7 | Moderate |
| Typical, some insulation, not air-sealed | 12.1 | Moderate |
| Older or poorly insulated, warm attic | 18.8 | High |
Sealing and insulating a typical attic takes out about 5.4 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 18.8 days.
Preventing ice dams on a Washington 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.
Washington winter, month by month
| Month | Snow (in) | Days on ground | Dam days |
|---|---|---|---|
| January | 6.8 | 15.6 | 5.3 |
| February | 5.2 | 10.2 | 3.0 |
| March | 2.8 | 3.6 | 0.7 |
| April | 0.8 | 0.4 | 0.0 |
| November | 1.5 | 1.8 | 0.3 |
| December | 5.2 | 9.4 | 2.7 |
Washington next to nearby towns
Washington ranks 155 of 225 Illinois cities here for ice-dam days, behind Arlington Heights at 21.5 days.
- East Peoria, IL 6 mi, 10.3 days
- Morton, IL 7 mi, 12.1 days
- Peoria, IL 10 mi, 10.3 days
- Pekin, IL 14 mi, 10.3 days
- Normal, IL 26 mi, 9.8 days
Where these numbers come from
NOAA 1991–2020 climate normals from Congerville 2NW, 11.7 miles from Washington. 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.