Ice dam risk in South Plainfield, NJ

How often ice dams form in South Plainfield

5.8 dam days a winter

Moderate risk. On an ordinary house in South Plainfield, conditions for an ice dam come on about 5.8 days in a normal winter, mostly in February and January.

South Plainfield 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 South Plainfield

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 South Plainfield 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 South Plainfield

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.

South Plainfield 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

South Plainfield next to nearby towns

South Plainfield ranks 27 of 116 New Jersey cities here for ice-dam days, behind Hopatcong at 14.7 days.

Plainfield, NJ 3 mi, 6.7 days
North Plainfield, NJ 3 mi, 6.7 days
Metuchen, NJ 4 mi, 5.8 days
Middlesex, NJ 4 mi, 5.8 days
Highland Park, NJ 5 mi, 6.2 days

Where these numbers come from

NOAA 1991–2020 climate normals from Plainfield, 2.1 miles from South Plainfield. 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.