Ice dam risk in Somerville, NJ
How often ice dams form in Somerville
5.8 dam days a winter
Moderate risk. On an ordinary house in Somerville, conditions for an ice dam come on about 5.8 days in a normal winter, mostly in February and January.
Somerville averages 21 inches of snow a year and about 27 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 Somerville
| Attic | Dam days | Risk |
|---|---|---|
| Air-sealed and well insulated | 4.5 | Low |
| Typical, some insulation, not air-sealed | 5.8 | Moderate |
| Older or poorly insulated, warm attic | 7.5 | Moderate |
The attic matters less in Somerville than in colder towns: there are only 1.3 days a winter between a typical attic and a sealed one.
What to do about ice dams in Somerville
- 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.
Somerville winter, month by month
| Month | Snow (in) | Days on ground | Dam days |
|---|---|---|---|
| January | 5.1 | 8.7 | 2.2 |
| February | 8.3 | 9.7 | 2.2 |
| March | 5.3 | 4.5 | 0.6 |
| April | 0.1 | 0.2 | 0.0 |
| November | 0.2 | 0.2 | 0.0 |
| December | 2.4 | 3.8 | 0.8 |
Somerville next to nearby towns
Somerville ranks 30 of 116 New Jersey cities here for ice-dam days, behind Hopatcong at 14.7 days.
- Manville, NJ 2 mi, 6.2 days
- Bound Brook, NJ 4 mi, 5.8 days
- Middlesex, NJ 6 mi, 5.8 days
- North Plainfield, NJ 10 mi, 6.7 days
- South Plainfield, NJ 10 mi, 5.8 days
Where these numbers come from
NOAA 1991–2020 climate normals from Plainfield, 11.0 miles from Somerville. 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.
- Snow-on-the-ground counts come from a second, nearby station, because the closest one does not record them.