Ice dam risk in Bloomington, IN
Will your roof get ice dams in Bloomington, IN?
5.1 dam days a winter
Moderate risk. On an ordinary house in Bloomington, conditions for an ice dam come on about 5.1 days in a normal winter, mostly in January and December.
Bloomington averages 18 inches of snow a year and about 20 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 Bloomington
| Attic | Dam days | Risk |
|---|---|---|
| Air-sealed and well insulated | 3.0 | Low |
| Typical, some insulation, not air-sealed | 5.1 | Moderate |
| Older or poorly insulated, warm attic | 7.7 | Moderate |
Sealing and insulating a typical attic takes out about 2.1 days a winter here. It drops the risk from moderate to low.
What to do about ice dams in Bloomington
- 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.
Which to spend on first: air sealing or heat cable.
Bloomington winter, month by month
| Month | Snow (in) | Days on ground | Dam days |
|---|---|---|---|
| January | 7.1 | 8.1 | 2.4 |
| February | 4.2 | 4.7 | 1.2 |
| March | 1.3 | 1.6 | 0.2 |
| April | 0.1 | 0.0 | 0.0 |
| October | 0.1 | 0.1 | 0.0 |
| November | 0.2 | 0.1 | 0.0 |
| December | 4.5 | 5.2 | 1.2 |
Bloomington next to nearby towns
Bloomington ranks 75 of 88 Indiana cities here for ice-dam days, behind Plymouth at 15.9 days.
- Martinsville, IN 18 mi, 5.1 days
- Bedford, IN 21 mi, 5.2 days
- Bargersville, IN 31 mi, 6.0 days
- Mooresville, IN 31 mi, 7.0 days
- Columbus, IN 32 mi, 4.8 days
Where these numbers come from
NOAA 1991–2020 climate normals from Bloomington Indiana Univ, 0.7 miles from Bloomington. 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.