Ice dam risk in Chatham, NJ
Will your roof get ice dams in Chatham, NJ?
5.7 dam days a winter
Moderate risk. On an ordinary house in Chatham, conditions for an ice dam come on about 5.7 days in a normal winter, mostly in January and February.
Chatham averages 24 inches of snow a year and about 24 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 Chatham
| Attic | Dam days | Risk |
|---|---|---|
| Air-sealed and well insulated | 4.3 | Low |
| Typical, some insulation, not air-sealed | 5.7 | Moderate |
| Older or poorly insulated, warm attic | 7.4 | Moderate |
The attic matters less in Chatham than in colder towns: there are only 1.4 days a winter between a typical attic and a sealed one.
What to do about ice dams in Chatham
- 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.
More on when a roof rake is worth it.
Chatham winter, month by month
| Month | Snow (in) | Days on ground | Dam days |
|---|---|---|---|
| January | 5.8 | 8.0 | 2.2 |
| February | 8.4 | 7.6 | 1.9 |
| March | 4.6 | 4.8 | 0.8 |
| April | 0.4 | 0.1 | 0.0 |
| November | 0.7 | 0.3 | 0.0 |
| December | 4.1 | 3.5 | 0.7 |
Chatham next to nearby towns
Chatham ranks 42 of 116 New Jersey cities here for ice-dam days, behind Hopatcong at 14.7 days.
- Summit, NJ 2 mi, 5.7 days
- Madison, NJ 2 mi, 5.7 days
- Florham Park, NJ 2 mi, 5.7 days
- New Providence, NJ 3 mi, 5.7 days
- Morristown, NJ 6 mi, 5.7 days
Where these numbers come from
NOAA 1991–2020 climate normals from Canoe Brook, 1.6 miles from Chatham. 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.