Ice dam risk in Moscow, ID
Ice dams in Moscow, ID: how often
11.0 dam days a winter
Moderate risk. On an ordinary house in Moscow, conditions for an ice dam come on about 11.0 days in a normal winter, mostly in January and December.
Moscow averages 51 inches of snow a year and about 46 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 Moscow
| Attic | Dam days | Risk |
|---|---|---|
| Air-sealed and well insulated | 7.7 | Moderate |
| Typical, some insulation, not air-sealed | 11.0 | Moderate |
| Older or poorly insulated, warm attic | 15.1 | High |
Sealing and insulating a typical attic takes out about 3.3 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 15.1 days.
What to do about ice dams in Moscow
- 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.
Moscow winter, month by month
| Month | Snow (in) | Days on ground | Dam days |
|---|---|---|---|
| January | 14.5 | 16.1 | 4.1 |
| February | 8.6 | 9.3 | 2.0 |
| March | 4.9 | 2.7 | 0.4 |
| April | 1.0 | 0.1 | 0.0 |
| May | 0.2 | 0.0 | 0.0 |
| October | 0.2 | 0.2 | 0.0 |
| November | 6.0 | 3.7 | 0.6 |
| December | 15.5 | 13.6 | 3.8 |
Moscow next to nearby towns
Moscow ranks 14 of 26 Idaho cities here for ice-dam days, behind Rexburg at 42.8 days.
- Pullman, WA 8 mi, 10.8 days
- Lewiston, ID 23 mi, 1.8 days
- Cheney, WA 59 mi, 13.0 days
- Liberty Lake, WA 65 mi, 13.0 days
- Spokane Valley, WA 65 mi, 13.0 days
Where these numbers come from
NOAA 1991–2020 climate normals from Moscow U Of I, 2.0 miles from Moscow. 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.