Ice dam risk in Rochester, NY
Will your roof get ice dams in Rochester, NY?
21.2 dam days a winter
High risk. On an ordinary house in Rochester, conditions for an ice dam come on about 21.2 days in a normal winter, mostly in January and February.
Rochester averages 102 inches of snow a year and about 72 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 Rochester
| Attic | Dam days | Risk |
|---|---|---|
| Air-sealed and well insulated | 10.8 | Moderate |
| Typical, some insulation, not air-sealed | 21.2 | High |
| Older or poorly insulated, warm attic | 34.2 | High |
Sealing and insulating a typical attic takes out about 10.4 days a winter here. It drops the risk from high to moderate. An older house with a warm attic should expect closer to 34.2 days.
What to do about ice dams in Rochester
- 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.
Rochester winter, month by month
| Month | Snow (in) | Days on ground | Dam days |
|---|---|---|---|
| January | 27.4 | 20.5 | 7.1 |
| February | 23.1 | 19.2 | 6.5 |
| March | 17.9 | 12.9 | 3.0 |
| April | 3.0 | 1.3 | 0.1 |
| May | 0.1 | 0.0 | 0.0 |
| October | 0.1 | 0.0 | 0.0 |
| November | 8.1 | 4.1 | 0.6 |
| December | 22.3 | 14.3 | 3.9 |
Rochester next to nearby towns
Rochester ranks 32 of 90 New York cities here for ice-dam days, behind Utica at 46.1 days.
- Canandaigua, NY 26 mi, 24.0 days
- Batavia, NY 31 mi, 19.5 days
- Geneva, NY 38 mi, 24.0 days
- Lockport, NY 54 mi, 21.4 days
- Auburn, NY 55 mi, 26.1 days
Where these numbers come from
NOAA 1991–2020 climate normals from Rochester Gtr International, 4.7 miles from Rochester. 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.