Ice dam risk in Garden City, ID
How often ice dams form in Garden City
14.5 dam days a winter
Moderate risk. On an ordinary house in Garden City, conditions for an ice dam come on about 14.5 days in a normal winter, mostly in January and December.
Garden City averages 57 inches of snow a year and about 60 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 Garden City
| Attic | Dam days | Risk |
|---|---|---|
| Air-sealed and well insulated | 9.8 | Moderate |
| Typical, some insulation, not air-sealed | 14.5 | Moderate |
| Older or poorly insulated, warm attic | 20.4 | High |
Sealing and insulating a typical attic takes out about 4.7 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 20.4 days.
Preventing ice dams on a Garden City 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.
Garden City winter, month by month
| Month | Snow (in) | Days on ground | Dam days |
|---|---|---|---|
| January | 14.0 | 19.2 | 5.4 |
| February | 9.2 | 12.5 | 2.6 |
| March | 6.6 | 4.2 | 0.5 |
| April | 2.4 | 0.1 | 0.0 |
| May | 0.7 | 0.1 | 0.0 |
| June | 0.1 | 0.0 | 0.0 |
| October | 0.4 | 0.0 | 0.0 |
| November | 7.3 | 5.6 | 0.9 |
| December | 16.7 | 18.0 | 5.1 |
Garden City next to nearby towns
Garden City ranks 11 of 26 Idaho cities here for ice-dam days, behind Rexburg at 42.8 days.
- Boise City, ID 6 mi, 4.0 days
- Eagle, ID 6 mi, 2.9 days
- Meridian, ID 7 mi, 4.0 days
- Star, ID 10 mi, 2.9 days
- Kuna, ID 11 mi, 4.0 days
Where these numbers come from
NOAA 1991–2020 climate normals from Boise 7 N, 6.7 miles from Garden 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 Garden City, so the snow figures may run high or low for the town itself.