Ice dam risk in Sandpoint, ID
Ice dams in Sandpoint, ID: how often
19.9 dam days a winter
High risk. On an ordinary house in Sandpoint, conditions for an ice dam come on about 19.9 days in a normal winter, mostly in January and December.
Sandpoint averages 62 inches of snow a year and about 72 days with snow on the ground. Snow that lies that long is what turns a little attic heat into a ridge of ice at the eave. 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 Sandpoint
| Attic | Dam days | Risk |
|---|---|---|
| Air-sealed and well insulated | 13.1 | Moderate |
| Typical, some insulation, not air-sealed | 19.9 | High |
| Older or poorly insulated, warm attic | 28.3 | High |
Sealing and insulating a typical attic takes out about 6.7 days a winter here. It drops the risk from high to moderate. An older house with a warm attic should expect closer to 28.3 days.
Preventing ice dams on a Sandpoint 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.
- At the next reroof, ask for ice-and-water membrane under the shingles from the eave to at least 24 inches inside the wall line. It does not stop a dam; it stops the leak when one forms.
Which to spend on first: air sealing or heat cable.
Sandpoint winter, month by month
| Month | Snow (in) | Days on ground | Dam days |
|---|---|---|---|
| January | 20.9 | 25.5 | 7.8 |
| February | 8.4 | 15.6 | 4.0 |
| March | 6.5 | 9.1 | 1.8 |
| April | 0.5 | 0.6 | 0.1 |
| November | 6.4 | 3.0 | 0.6 |
| December | 19.3 | 18.2 | 5.6 |
Sandpoint next to nearby towns
Sandpoint ranks 6 of 26 Idaho cities here for ice-dam days, behind Rexburg at 42.8 days.
- Rathdrum, ID 37 mi, 13.1 days
- Hayden, ID 37 mi, 16.7 days
- Coeur d'Alene, ID 41 mi, 16.7 days
- Post Falls, ID 42 mi, 13.1 days
- Liberty Lake, WA 49 mi, 13.0 days
Where these numbers come from
NOAA 1991–2020 climate normals from Sandpoint Exp Station, 0.9 miles from Sandpoint. 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.