Ice dam risk in Jackson, WY
How often ice dams form in Jackson
50.0 dam days a winter
Severe risk. On an ordinary house in Jackson, conditions for an ice dam come on about 50.0 days in a normal winter, mostly in January and December.
Jackson averages 78 inches of snow a year and about 154 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 Jackson
| Attic | Dam days | Risk |
|---|---|---|
| Air-sealed and well insulated | 27.6 | High |
| Typical, some insulation, not air-sealed | 50.0 | Severe |
| Older or poorly insulated, warm attic | 78.1 | Severe |
Sealing and insulating a typical attic takes out about 22.4 days a winter here. It drops the risk from severe to high. An older house with a warm attic should expect closer to 78.1 days.
What to do about ice dams in Jackson
- 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.
- Heat cable is worth pricing here even on a sealed house, along the eave and in the gutters and downspouts it drains into.
Running 60 feet of 5 W/ft cable whenever snow lies below freezing would use about 404 kWh a winter in Jackson, roughly $69 at 17 cents a kWh.
Which to spend on first: air sealing or heat cable.
Jackson winter, month by month
| Month | Snow (in) | Days on ground | Dam days |
|---|---|---|---|
| January | 19.1 | 31.0 | 12.3 |
| February | 15.6 | 28.5 | 9.7 |
| March | 9.2 | 30.4 | 7.9 |
| April | 4.2 | 14.8 | 3.1 |
| May | 0.6 | 0.8 | 0.1 |
| September | 0.1 | 0.1 | 0.0 |
| October | 2.0 | 2.4 | 0.5 |
| November | 11.0 | 15.8 | 4.5 |
| December | 16.4 | 30.0 | 11.9 |
Jackson next to nearby towns
Jackson ranks 1 of 11 Wyoming cities here for ice-dam days, the worst in the state.
- Rexburg, ID 56 mi, 42.8 days
- Ammon, ID 59 mi, 36.4 days
- Idaho Falls, ID 63 mi, 36.4 days
- Blackfoot, ID 81 mi, 20.1 days
- Chubbuck, ID 93 mi, 20.8 days
Where these numbers come from
NOAA 1991–2020 climate normals from Jackson, 1.2 miles from Jackson. 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.