Ice dam risk in Gillette, WY
Ice dams in Gillette, WY: how often
18.7 dam days a winter
High risk. On an ordinary house in Gillette, conditions for an ice dam come on about 18.7 days in a normal winter, mostly in January and December.
Gillette averages 56 inches of snow a year and about 66 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 Gillette
| Attic | Dam days | Risk |
|---|---|---|
| Air-sealed and well insulated | 11.8 | Moderate |
| Typical, some insulation, not air-sealed | 18.7 | High |
| Older or poorly insulated, warm attic | 27.3 | High |
Sealing and insulating a typical attic takes out about 6.9 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.
What to do about ice dams in Gillette
- 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.
Gillette winter, month by month
| Month | Snow (in) | Days on ground | Dam days |
|---|---|---|---|
| January | 8.2 | 16.2 | 5.2 |
| February | 9.0 | 13.8 | 4.3 |
| March | 8.6 | 7.9 | 1.9 |
| April | 9.4 | 3.7 | 0.6 |
| May | 1.3 | 0.2 | 0.0 |
| June | 0.1 | 0.0 | 0.0 |
| September | 0.5 | 0.2 | 0.0 |
| October | 4.4 | 2.2 | 0.3 |
| November | 5.8 | 7.4 | 1.8 |
| December | 8.4 | 14.2 | 4.6 |
Gillette next to nearby towns
Gillette ranks 7 of 11 Wyoming cities here for ice-dam days, behind Jackson at 50.0 days.
- Sheridan, WY 81 mi, 22.9 days
- Spearfish, SD 84 mi, 17.4 days
- Casper, WY 107 mi, 18.5 days
- Rapid City, SD 114 mi, 11.8 days
- Box Elder, SD 120 mi, 13.9 days
Where these numbers come from
NOAA 1991–2020 climate normals from Gillette 4SE, 2.5 miles from Gillette. 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.