Ice dam risk in Boise City, ID
How often ice dams form in Boise City
4.0 dam days a winter
Low risk. On an ordinary house in Boise City, conditions for an ice dam come on about 4.0 days in a normal winter, mostly in January and December.
Boise City averages 18 inches of snow a year and about 17 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 Boise City
| Attic | Dam days | Risk |
|---|---|---|
| Air-sealed and well insulated | 2.8 | Low |
| Typical, some insulation, not air-sealed | 4.0 | Low |
| Older or poorly insulated, warm attic | 5.4 | Moderate |
The attic matters less in Boise City than in colder towns: there are only 1.2 days a winter between a typical attic and a sealed one.
Preventing ice dams on a Boise City roof
- Check the gutters before the first snow and clear them, so meltwater has somewhere to go. If you see icicles thicker than a finger along the eave after a storm, that is the early sign to look at the attic.
Snowy places are not always the worst: why snowfall misleads.
Boise City winter, month by month
| Month | Snow (in) | Days on ground | Dam days |
|---|---|---|---|
| January | 5.3 | 6.4 | 1.6 |
| February | 3.3 | 2.6 | 0.5 |
| March | 1.2 | 0.5 | 0.0 |
| April | 0.1 | 0.0 | 0.0 |
| October | 0.1 | 0.0 | 0.0 |
| November | 2.0 | 1.8 | 0.3 |
| December | 5.6 | 5.9 | 1.5 |
Boise City next to nearby towns
Boise City ranks 16 of 26 Idaho cities here for ice-dam days, behind Rexburg at 42.8 days.
- Garden City, ID 6 mi, 14.5 days
- Meridian, ID 9 mi, 4.0 days
- Kuna, ID 10 mi, 4.0 days
- Eagle, ID 11 mi, 2.9 days
- Star, ID 15 mi, 2.9 days
Where these numbers come from
NOAA 1991–2020 climate normals from Boise Air Terminal, 2.2 miles from Boise City. 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.
- The nearest weather station sits at a noticeably different elevation from Boise City, so the snow figures may run high or low for the town itself.