Ice dam risk in Spokane, WA
Will your roof get ice dams in Spokane, WA?
13.0 dam days a winter
Moderate risk. On an ordinary house in Spokane, conditions for an ice dam come on about 13.0 days in a normal winter, mostly in January and December.
Spokane averages 45 inches of snow a year and about 48 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 Spokane
| Attic | Dam days | Risk |
|---|---|---|
| Air-sealed and well insulated | 7.5 | Moderate |
| Typical, some insulation, not air-sealed | 13.0 | Moderate |
| Older or poorly insulated, warm attic | 19.9 | High |
Sealing and insulating a typical attic takes out about 5.5 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 19.9 days.
What to do about ice dams in Spokane
- 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.
Spokane winter, month by month
| Month | Snow (in) | Days on ground | Dam days |
|---|---|---|---|
| January | 12.3 | 15.9 | 4.8 |
| February | 7.8 | 10.2 | 2.5 |
| March | 3.9 | 3.9 | 0.6 |
| April | 0.7 | 0.1 | 0.0 |
| May | 0.1 | 0.0 | 0.0 |
| September | 0.1 | 0.0 | 0.0 |
| October | 0.5 | 0.3 | 0.0 |
| November | 6.2 | 4.4 | 0.8 |
| December | 13.8 | 13.2 | 4.2 |
Spokane next to nearby towns
Spokane ranks 1 of 91 Washington cities here for ice-dam days, the worst in the state.
- Airway Heights, WA 7 mi, 13.0 days
- Spokane Valley, WA 9 mi, 13.0 days
- Cheney, WA 14 mi, 13.0 days
- Liberty Lake, WA 15 mi, 13.0 days
- Post Falls, ID 23 mi, 13.1 days
Where these numbers come from
NOAA 1991–2020 climate normals from Spokane International Airport, 5.4 miles from Spokane. 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.