Ice dam risk in Watertown, MA
Ice dams in Watertown, MA: how often
14.8 dam days a winter
Moderate risk. On an ordinary house in Watertown, conditions for an ice dam come on about 14.8 days in a normal winter, mostly in January and February.
Watertown averages 49 inches of snow a year and about 68 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 Watertown
| Attic | Dam days | Risk |
|---|---|---|
| Air-sealed and well insulated | 9.5 | Moderate |
| Typical, some insulation, not air-sealed | 14.8 | Moderate |
| Older or poorly insulated, warm attic | 21.6 | High |
Sealing and insulating a typical attic takes out about 5.4 days a winter here. It does not move the risk band, but it shortens every dam. An older house with a warm attic should expect closer to 21.6 days.
What to do about ice dams in Watertown
- 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.
Which to spend on first: air sealing or heat cable.
Watertown winter, month by month
| Month | Snow (in) | Days on ground | Dam days |
|---|---|---|---|
| January | 14.3 | 20.2 | 5.6 |
| February | 14.4 | 18.8 | 4.7 |
| March | 9.0 | 13.2 | 2.0 |
| April | 1.6 | 1.2 | 0.0 |
| October | 0.2 | 0.0 | 0.0 |
| November | 0.7 | 1.7 | 0.1 |
| December | 9.0 | 12.5 | 2.4 |
Watertown next to nearby towns
Watertown ranks 28 of 58 Massachusetts cities here for ice-dam days, behind Pittsfield at 31.3 days.
- Newton, MA 3 mi, 16.0 days
- Cambridge, MA 3 mi, 13.7 days
- Waltham, MA 4 mi, 18.8 days
- Somerville, MA 4 mi, 13.7 days
- Medford, MA 5 mi, 13.7 days
Where these numbers come from
NOAA 1991–2020 climate normals from Boston, 8.6 miles from Watertown. 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.