Ice dam risk in Ossining, NY
How often ice dams form in Ossining
15.5 dam days a winter
High risk. On an ordinary house in Ossining, conditions for an ice dam come on about 15.5 days in a normal winter, mostly in February and January.
Ossining averages 40 inches of snow a year and about 58 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 Ossining
| Attic | Dam days | Risk |
|---|---|---|
| Air-sealed and well insulated | 9.5 | Moderate |
| Typical, some insulation, not air-sealed | 15.5 | High |
| Older or poorly insulated, warm attic | 23.0 | High |
Sealing and insulating a typical attic takes out about 6.0 days a winter here. It drops the risk from high to moderate. An older house with a warm attic should expect closer to 23.0 days.
Preventing ice dams on a Ossining 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.
- 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.
Ossining winter, month by month
| Month | Snow (in) | Days on ground | Dam days |
|---|---|---|---|
| January | 8.8 | 18.1 | 5.8 |
| February | 12.6 | 17.8 | 5.2 |
| March | 8.2 | 10.8 | 2.0 |
| April | 1.8 | 0.7 | 0.0 |
| November | 0.5 | 0.8 | 0.1 |
| December | 7.6 | 10.1 | 2.4 |
Ossining next to nearby towns
Ossining ranks 47 of 90 New York cities here for ice-dam days, behind Utica at 46.1 days.
- Sleepy Hollow, NY 4 mi, 8.7 days
- Haverstraw, NY 4 mi, 15.5 days
- Tarrytown, NY 6 mi, 8.7 days
- West Haverstraw, NY 7 mi, 15.5 days
- Mount Kisco, NY 8 mi, 15.5 days
Where these numbers come from
NOAA 1991–2020 climate normals from Yorktown Hts 1W, 8.7 miles from Ossining. 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.