Ice dam risk in Twin Falls, ID
How often ice dams form in Twin Falls
17.0 dam days a winter
High risk. On an ordinary house in Twin Falls, conditions for an ice dam come on about 17.0 days in a normal winter, mostly in January and February.
Twin Falls averages 24 inches of snow a year and about 62 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 Twin Falls
| Attic | Dam days | Risk |
|---|---|---|
| Air-sealed and well insulated | 11.7 | Moderate |
| Typical, some insulation, not air-sealed | 17.0 | High |
| Older or poorly insulated, warm attic | 23.5 | High |
Sealing and insulating a typical attic takes out about 5.3 days a winter here. It drops the risk from high to moderate. An older house with a warm attic should expect closer to 23.5 days.
Preventing ice dams on a Twin Falls 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.
Twin Falls winter, month by month
| Month | Snow (in) | Days on ground | Dam days |
|---|---|---|---|
| January | 7.8 | 24.0 | 7.2 |
| February | 5.5 | 14.8 | 3.9 |
| March | 1.9 | 7.1 | 1.3 |
| April | 0.5 | 0.2 | 0.0 |
| October | 0.5 | 0.2 | 0.0 |
| November | 2.0 | 1.9 | 0.4 |
| December | 6.0 | 13.8 | 4.1 |
Twin Falls next to nearby towns
Twin Falls ranks 7 of 26 Idaho cities here for ice-dam days, behind Rexburg at 42.8 days.
- Jerome, ID 11 mi, 17.0 days
- Burley, ID 34 mi, 3.1 days
- Mountain Home, ID 74 mi, 4.0 days
- Pocatello, ID 104 mi, 9.4 days
- Chubbuck, ID 105 mi, 20.8 days
Where these numbers come from
NOAA 1991–2020 climate normals from Twin Falls 6 E, 6.0 miles from Twin Falls. 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.
- Snow-on-the-ground counts come from a second, nearby station, because the closest one does not record them.