Ice dam risk in Decatur, IN
Ice dams in Decatur, IN: how often
11.4 dam days a winter
Moderate risk. On an ordinary house in Decatur, conditions for an ice dam come on about 11.4 days in a normal winter, mostly in January and February.
Decatur averages 28 inches of snow a year and about 38 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 Decatur
| Attic | Dam days | Risk |
|---|---|---|
| Air-sealed and well insulated | 5.8 | Moderate |
| Typical, some insulation, not air-sealed | 11.4 | Moderate |
| Older or poorly insulated, warm attic | 18.4 | High |
Sealing and insulating a typical attic takes out about 5.6 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 18.4 days.
Preventing ice dams on a Decatur 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.
Decatur winter, month by month
| Month | Snow (in) | Days on ground | Dam days |
|---|---|---|---|
| January | 9.2 | 14.1 | 4.8 |
| February | 7.5 | 10.5 | 3.4 |
| March | 4.2 | 4.1 | 0.8 |
| April | 0.5 | 0.3 | 0.0 |
| November | 1.2 | 1.5 | 0.2 |
| December | 5.5 | 7.6 | 2.1 |
Decatur next to nearby towns
Decatur ranks 34 of 88 Indiana cities here for ice-dam days, behind Plymouth at 15.9 days.
- Bluffton, IN 14 mi, 10.6 days
- New Haven, IN 17 mi, 11.4 days
- Van Wert, OH 18 mi, 6.0 days
- Fort Wayne, IN 21 mi, 11.4 days
- Celina, OH 27 mi, 5.7 days
Where these numbers come from
NOAA 1991–2020 climate normals from Decatur 1 N, 1.3 miles from Decatur. 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.