Ice dam risk in Casper, WY
Ice dams in Casper, WY: how often
18.5 dam days a winter
High risk. On an ordinary house in Casper, conditions for an ice dam come on about 18.5 days in a normal winter, mostly in January and December.
Casper averages 72 inches of snow a year and about 64 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 Casper
| Attic | Dam days | Risk |
|---|---|---|
| Air-sealed and well insulated | 11.5 | Moderate |
| Typical, some insulation, not air-sealed | 18.5 | High |
| Older or poorly insulated, warm attic | 27.3 | High |
Sealing and insulating a typical attic takes out about 7.0 days a winter here. It drops the risk from high to moderate. An older house with a warm attic should expect closer to 27.3 days.
Preventing ice dams on a Casper 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.
Casper winter, month by month
| Month | Snow (in) | Days on ground | Dam days |
|---|---|---|---|
| January | 9.0 | 17.2 | 5.5 |
| February | 10.9 | 12.1 | 3.7 |
| March | 10.3 | 6.1 | 1.4 |
| April | 10.5 | 3.0 | 0.6 |
| May | 2.6 | 0.6 | 0.0 |
| June | 0.1 | 0.1 | 0.0 |
| September | 1.5 | 0.2 | 0.0 |
| October | 7.0 | 2.0 | 0.3 |
| November | 8.9 | 6.8 | 1.7 |
| December | 11.0 | 16.3 | 5.3 |
Casper next to nearby towns
Casper ranks 8 of 11 Wyoming cities here for ice-dam days, behind Jackson at 50.0 days.
- Riverton, WY 105 mi, 25.7 days
- Gillette, WY 107 mi, 18.7 days
- Laramie, WY 112 mi, 32.6 days
- Sheridan, WY 139 mi, 22.9 days
- Cheyenne, WY 142 mi, 10.3 days
Where these numbers come from
NOAA 1991–2020 climate normals from Casper-Natrona County Airport, 8.6 miles from Casper. 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.