Ice dam risk in Jamestown, NY
How often ice dams form in Jamestown
25.4 dam days a winter
High risk. On an ordinary house in Jamestown, conditions for an ice dam come on about 25.4 days in a normal winter, mostly in January and February.
Jamestown averages 98 inches of snow a year and about 81 days with snow on the ground. Snow that lies that long is what turns a little attic heat into a ridge of ice at the eave. 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 Jamestown
| Attic | Dam days | Risk |
|---|---|---|
| Air-sealed and well insulated | 12.8 | Moderate |
| Typical, some insulation, not air-sealed | 25.4 | High |
| Older or poorly insulated, warm attic | 41.1 | Severe |
Sealing and insulating a typical attic takes out about 12.6 days a winter here. It drops the risk from high to moderate. An older house with a warm attic should expect closer to 41.1 days.
What to do about ice dams in Jamestown
- 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.
- At the next reroof, ask for ice-and-water membrane under the shingles from the eave to at least 24 inches inside the wall line. It does not stop a dam; it stops the leak when one forms.
Which to spend on first: air sealing or heat cable.
Jamestown winter, month by month
| Month | Snow (in) | Days on ground | Dam days |
|---|---|---|---|
| January | 29.8 | 23.8 | 8.7 |
| February | 19.3 | 21.1 | 7.3 |
| March | 15.3 | 13.4 | 3.4 |
| April | 2.7 | 1.5 | 0.2 |
| October | 0.4 | 0.3 | 0.0 |
| November | 9.3 | 5.3 | 1.0 |
| December | 21.6 | 15.5 | 4.8 |
Jamestown next to nearby towns
Jamestown ranks 15 of 90 New York cities here for ice-dam days, behind Utica at 46.1 days.
- Dunkirk, NY 27 mi, 25.0 days
- Olean, NY 41 mi, 22.7 days
- Erie, PA 43 mi, 17.1 days
- Lackawanna, NY 54 mi, 21.2 days
- Meadville, PA 56 mi, 19.8 days
Where these numbers come from
NOAA 1991–2020 climate normals from Jamestown 4 ENE, 4.0 miles from Jamestown. 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.