Ice dam risk in Manassas, VA
How often ice dams form in Manassas
2.8 dam days a winter
Low risk. On an ordinary house in Manassas, conditions for an ice dam come on about 2.8 days in a normal winter, mostly in February and January.
Manassas averages 21 inches of snow a year and about 14 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 Manassas
| Attic | Dam days | Risk |
|---|---|---|
| Air-sealed and well insulated | 2.2 | Low |
| Typical, some insulation, not air-sealed | 2.8 | Low |
| Older or poorly insulated, warm attic | 3.5 | Low |
The attic matters less in Manassas than in colder towns: there are only 0.6 days a winter between a typical attic and a sealed one.
What to do about ice dams in Manassas
- 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.
Manassas winter, month by month
| Month | Snow (in) | Days on ground | Dam days |
|---|---|---|---|
| January | 6.9 | 4.4 | 1.1 |
| February | 7.0 | 5.2 | 1.1 |
| March | 3.9 | 2.2 | 0.3 |
| April | 0.1 | 0.0 | 0.0 |
| November | 0.3 | 0.1 | 0.0 |
| December | 2.8 | 1.9 | 0.4 |
Manassas next to nearby towns
Manassas ranks 15 of 39 Virginia cities here for ice-dam days, behind Winchester at 4.7 days.
- Manassas Park, VA 3 mi, 2.8 days
- Fairfax, VA 12 mi, 3.7 days
- Vienna, VA 16 mi, 3.7 days
- Herndon, VA 16 mi, 2.8 days
- Warrenton, VA 17 mi, 4.5 days
Where these numbers come from
NOAA 1991–2020 climate normals from Washington Dulles International Airport, 13.1 miles from Manassas. 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.