Ice dam risk in Ithaca, NY
Will your roof get ice dams in Ithaca, NY?
22.7 dam days a winter
High risk. On an ordinary house in Ithaca, conditions for an ice dam come on about 22.7 days in a normal winter, mostly in January and February.
Ithaca averages 63 inches of snow a year and about 73 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 Ithaca
| Attic | Dam days | Risk |
|---|---|---|
| Air-sealed and well insulated | 11.3 | Moderate |
| Typical, some insulation, not air-sealed | 22.7 | High |
| Older or poorly insulated, warm attic | 37.0 | Severe |
Sealing and insulating a typical attic takes out about 11.5 days a winter here. It drops the risk from high to moderate. An older house with a warm attic should expect closer to 37.0 days.
What to do about ice dams in Ithaca
- 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.
Ithaca winter, month by month
| Month | Snow (in) | Days on ground | Dam days |
|---|---|---|---|
| January | 16.6 | 20.6 | 7.5 |
| February | 14.5 | 19.6 | 6.7 |
| March | 12.0 | 13.0 | 3.4 |
| April | 2.8 | 1.4 | 0.2 |
| October | 0.2 | 0.1 | 0.0 |
| November | 4.6 | 4.0 | 0.7 |
| December | 12.2 | 14.0 | 4.2 |
Ithaca next to nearby towns
Ithaca ranks 25 of 90 New York cities here for ice-dam days, behind Utica at 46.1 days.
- Cortland, NY 20 mi, 24.8 days
- Elmira, NY 29 mi, 17.2 days
- Endicott, NY 33 mi, 26.0 days
- Auburn, NY 34 mi, 26.1 days
- Corning, NY 35 mi, 24.0 days
Where these numbers come from
NOAA 1991–2020 climate normals from Ithaca Cornell Univ, 2.8 miles from Ithaca. 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.