Ice dam risk in Rockville, MD
How often ice dams form in Rockville
1.1 dam days a winter
Low risk. On an ordinary house in Rockville, conditions for an ice dam come on about 1.1 days in a normal winter, mostly in January and February.
Rockville 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 Rockville
| 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 Rockville than in colder towns: there are only 0.2 days a winter between a typical attic and a sealed one.
What to do about ice dams in Rockville
- 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.
Rockville winter, month by month
| Month | Snow (in) | Days on ground | Dam days |
|---|---|---|---|
| January | 2.9 | 2.1 | 0.5 |
| February | 1.4 | 1.8 | 0.4 |
| March | 0.7 | 0.8 | 0.1 |
| December | 0.8 | 0.8 | 0.1 |
Rockville next to nearby towns
Rockville ranks 22 of 23 Maryland cities here for ice-dam days, behind Hagerstown at 12.1 days.
- Gaithersburg, MD 5 mi, 5.8 days
- Takoma Park, MD 11 mi, 2.1 days
- College Park, MD 13 mi, 2.9 days
- Hyattsville, MD 14 mi, 2.1 days
- Falls Church, VA 14 mi, 1.1 days
Where these numbers come from
NOAA 1991–2020 climate normals from Dalecarlia Rsvr, 10.3 miles from Rockville. 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.