Ice dam risk in Sheridan, WY
Ice dams in Sheridan, WY: how often
22.9 dam days a winter
High risk. On an ordinary house in Sheridan, conditions for an ice dam come on about 22.9 days in a normal winter, mostly in January and February.
Sheridan averages 33 inches of snow a year and about 75 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 Sheridan
| Attic | Dam days | Risk |
|---|---|---|
| Air-sealed and well insulated | 14.9 | Moderate |
| Typical, some insulation, not air-sealed | 22.9 | High |
| Older or poorly insulated, warm attic | 33.0 | High |
Sealing and insulating a typical attic takes out about 8.1 days a winter here. It drops the risk from high to moderate. An older house with a warm attic should expect closer to 33.0 days.
Preventing ice dams on a Sheridan 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.
Sheridan winter, month by month
| Month | Snow (in) | Days on ground | Dam days |
|---|---|---|---|
| January | 7.8 | 21.9 | 7.4 |
| February | 4.2 | 18.1 | 5.7 |
| March | 4.5 | 8.9 | 2.3 |
| April | 5.3 | 3.0 | 0.5 |
| May | 0.6 | 0.4 | 0.0 |
| September | 0.1 | 0.1 | 0.0 |
| October | 2.4 | 1.7 | 0.3 |
| November | 3.1 | 6.5 | 1.8 |
| December | 5.2 | 14.6 | 4.9 |
Sheridan next to nearby towns
Sheridan ranks 6 of 11 Wyoming cities here for ice-dam days, behind Jackson at 50.0 days.
- Gillette, WY 81 mi, 18.7 days
- Billings, MT 103 mi, 14.3 days
- Cody, WY 105 mi, 7.3 days
- Casper, WY 139 mi, 18.5 days
- Riverton, WY 141 mi, 25.7 days
Where these numbers come from
NOAA 1991–2020 climate normals from Sheridan Field Station, 6.9 miles from Sheridan. 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.