Ice dam risk in Vienna, VA
Will your roof get ice dams in Vienna, VA?
3.7 dam days a winter
Low risk. On an ordinary house in Vienna, conditions for an ice dam come on about 3.7 days in a normal winter, mostly in February and January.
Vienna averages 19 inches of snow a year and about 17 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 Vienna
| Attic | Dam days | Risk |
|---|---|---|
| Air-sealed and well insulated | 2.8 | Low |
| Typical, some insulation, not air-sealed | 3.7 | Low |
| Older or poorly insulated, warm attic | 4.8 | Low |
The attic matters less in Vienna than in colder towns: there are only 0.9 days a winter between a typical attic and a sealed one.
Preventing ice dams on a Vienna 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.
Vienna winter, month by month
| Month | Snow (in) | Days on ground | Dam days |
|---|---|---|---|
| January | 6.5 | 5.6 | 1.4 |
| February | 7.5 | 6.4 | 1.4 |
| March | 2.0 | 2.1 | 0.3 |
| November | 0.1 | 0.1 | 0.0 |
| December | 2.4 | 3.0 | 0.6 |
Vienna next to nearby towns
Vienna ranks 11 of 39 Virginia cities here for ice-dam days, behind Winchester at 4.7 days.
- Fairfax, VA 4 mi, 3.7 days
- Falls Church, VA 5 mi, 1.1 days
- Herndon, VA 9 mi, 2.8 days
- Alexandria, VA 11 mi, 1.5 days
- Washington, DC 13 mi, 2.1 days
Where these numbers come from
NOAA 1991–2020 climate normals from Vienna, 1.7 miles from Vienna. 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.