Ice dam risk in Woodstock, IL
Ice dams in Woodstock, IL: how often
16.8 dam days a winter
High risk. On an ordinary house in Woodstock, conditions for an ice dam come on about 16.8 days in a normal winter, mostly in January and February.
Woodstock averages 35 inches of snow a year and about 54 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 Woodstock
| Attic | Dam days | Risk |
|---|---|---|
| Air-sealed and well insulated | 9.0 | Moderate |
| Typical, some insulation, not air-sealed | 16.8 | High |
| Older or poorly insulated, warm attic | 26.6 | High |
Sealing and insulating a typical attic takes out about 7.8 days a winter here. It drops the risk from high to moderate. An older house with a warm attic should expect closer to 26.6 days.
Preventing ice dams on a Woodstock 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.
Woodstock winter, month by month
| Month | Snow (in) | Days on ground | Dam days |
|---|---|---|---|
| January | 10.0 | 18.0 | 6.3 |
| February | 9.0 | 16.6 | 5.9 |
| March | 4.4 | 6.7 | 1.3 |
| April | 1.2 | 0.5 | 0.0 |
| October | 0.2 | 0.0 | 0.0 |
| November | 1.6 | 1.7 | 0.3 |
| December | 8.7 | 10.6 | 3.0 |
Woodstock next to nearby towns
Woodstock ranks 41 of 225 Illinois cities here for ice-dam days, behind Arlington Heights at 21.5 days.
- Crystal Lake, IL 7 mi, 16.8 days
- McHenry, IL 8 mi, 18.8 days
- Huntley, IL 10 mi, 16.8 days
- Lake in the Hills, IL 11 mi, 16.8 days
- Cary, IL 12 mi, 18.8 days
Where these numbers come from
NOAA 1991–2020 climate normals from Crystal Lake 4NW, 3.9 miles from Woodstock. 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.