Ice dam risk in Hagerstown, MD
Ice dams in Hagerstown, MD: how often
12.1 dam days a winter
Moderate risk. On an ordinary house in Hagerstown, conditions for an ice dam come on about 12.1 days in a normal winter, mostly in January and February.
Hagerstown averages 33 inches of snow a year and about 44 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 Hagerstown
| Attic | Dam days | Risk |
|---|---|---|
| Air-sealed and well insulated | 7.1 | Moderate |
| Typical, some insulation, not air-sealed | 12.1 | Moderate |
| Older or poorly insulated, warm attic | 18.5 | High |
Sealing and insulating a typical attic takes out about 5.1 days a winter here. It does not move the risk band, but it shortens every dam. An older house with a warm attic should expect closer to 18.5 days.
What to do about ice dams in Hagerstown
- 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.
Which to spend on first: air sealing or heat cable.
Hagerstown winter, month by month
| Month | Snow (in) | Days on ground | Dam days |
|---|---|---|---|
| January | 10.6 | 13.6 | 4.3 |
| February | 9.5 | 13.6 | 4.1 |
| March | 6.5 | 7.8 | 1.6 |
| April | 0.6 | 0.4 | 0.0 |
| November | 0.6 | 1.0 | 0.1 |
| December | 5.2 | 7.2 | 1.9 |
Hagerstown next to nearby towns
Hagerstown ranks 1 of 23 Maryland cities here for ice-dam days, the worst in the state.
- Waynesboro, PA 11 mi, 12.1 days
- Martinsburg, WV 18 mi, 4.7 days
- Chambersburg, PA 21 mi, 7.4 days
- Frederick, MD 22 mi, 5.8 days
- Leesburg, VA 38 mi, 2.8 days
Where these numbers come from
NOAA 1991–2020 climate normals from S Mtn, 18.8 miles from Hagerstown. 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.