Ice dam risk in Pottstown, PA

How often ice dams form in Pottstown

8.7 dam days a winter

Moderate risk. On an ordinary house in Pottstown, conditions for an ice dam come on about 8.7 days in a normal winter, mostly in February and January.

Pottstown averages 13 inches of snow a year and about 34 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 Pottstown

Attic	Dam days	Risk
Air-sealed and well insulated	6.3	Moderate
Typical, some insulation, not air-sealed	8.7	Moderate
Older or poorly insulated, warm attic	11.6	Moderate

Sealing and insulating a typical attic takes out about 2.3 days a winter here. It does not move the risk band, but it shortens every dam.

Preventing ice dams on a Pottstown roof

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.

Which to spend on first: air sealing or heat cable.

Pottstown winter, month by month

Month	Snow (in)	Days on ground	Dam days
January	3.9	10.6	3.1
February	5.4	14.2	3.7
March	1.3	4.2	0.8
April	0.1	0.1	0.0
November	0.0	0.5	0.1
December	2.2	4.2	1.0

Pottstown next to nearby towns

Pottstown ranks 40 of 68 Pennsylvania cities here for ice-dam days, behind St. Marys at 26.9 days.

Phoenixville, PA 10 mi, 8.7 days
Reading, PA 16 mi, 7.6 days
Wyomissing, PA 18 mi, 7.6 days
Norristown, PA 18 mi, 3.3 days
Lansdale, PA 19 mi, 4.6 days

Where these numbers come from

NOAA 1991–2020 climate normals from Graterford 1 E, 11.7 miles from Pottstown. 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.