Ice dam risk in Hopatcong, NJ
Will your roof get ice dams in Hopatcong, NJ?
14.7 dam days a winter
Moderate risk. On an ordinary house in Hopatcong, conditions for an ice dam come on about 14.7 days in a normal winter, mostly in January and February.
Hopatcong averages 39 inches of snow a year and about 52 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 Hopatcong
| Attic | Dam days | Risk |
|---|---|---|
| Air-sealed and well insulated | 9.6 | Moderate |
| Typical, some insulation, not air-sealed | 14.7 | Moderate |
| Older or poorly insulated, warm attic | 21.0 | 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 21.0 days.
What to do about ice dams in Hopatcong
- 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.
Hopatcong winter, month by month
| Month | Snow (in) | Days on ground | Dam days |
|---|---|---|---|
| January | 11.6 | 17.1 | 5.6 |
| February | 9.9 | 14.9 | 4.3 |
| March | 6.3 | 9.0 | 1.9 |
| April | 1.2 | 0.3 | 0.0 |
| October | 0.3 | 0.1 | 0.0 |
| November | 1.4 | 0.8 | 0.1 |
| December | 8.0 | 10.2 | 2.7 |
Hopatcong next to nearby towns
Hopatcong ranks 1 of 116 New Jersey cities here for ice-dam days, the worst in the state.
- Dover, NJ 7 mi, 5.7 days
- Hackettstown, NJ 11 mi, 12.4 days
- Morristown, NJ 14 mi, 5.7 days
- Kinnelon, NJ 15 mi, 5.7 days
- Madison, NJ 19 mi, 5.7 days
Where these numbers come from
NOAA 1991–2020 climate normals from Sussex 1 NW, 18.6 miles from Hopatcong. 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.