Ice dam risk in Johnson City, TN
Will your roof get ice dams in Johnson City, TN?
1.1 dam days a winter
Low risk. On an ordinary house in Johnson City, conditions for an ice dam come on about 1.1 days in a normal winter, mostly in January and February.
Johnson City averages 6 inches of snow a year and about 6 days with snow on the ground. Most of it comes and goes within a few days. 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 Johnson City
| Attic | Dam days | Risk |
|---|---|---|
| Air-sealed and well insulated | 0.9 | Very unlikely |
| Typical, some insulation, not air-sealed | 1.1 | Low |
| Older or poorly insulated, warm attic | 1.3 | Low |
The attic matters less in Johnson City than in colder towns: there are only 0.2 days a winter between a typical attic and a sealed one.
Preventing ice dams on a Johnson City roof
- Check the gutters before the first snow and clear them, so meltwater has somewhere to go. If you see icicles thicker than a finger along the eave after a storm, that is the early sign to look at the attic.
Snowy places are not always the worst: why snowfall misleads.
Johnson City winter, month by month
| Month | Snow (in) | Days on ground | Dam days |
|---|---|---|---|
| January | 1.9 | 2.5 | 0.5 |
| February | 2.1 | 1.4 | 0.2 |
| March | 0.1 | 0.4 | 0.0 |
| November | 0.1 | 0.2 | 0.0 |
| December | 1.8 | 1.3 | 0.2 |
Johnson City next to nearby towns
Johnson City ranks 5 of 65 Tennessee cities here for ice-dam days, behind Crossville at 2.6 days.
- Elizabethton, TN 8 mi, 1.1 days
- Kingsport, TN 15 mi, 0.6 days
- Bristol, TN 17 mi, 1.2 days
- Bristol, VA 23 mi, 1.2 days
- Greeneville, TN 27 mi, 1.2 days
Where these numbers come from
NOAA 1991–2020 climate normals from Elizabethton, 7.4 miles from Johnson City. 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.