Ice dam risk in Norwich, CT
How often ice dams form in Norwich
7.5 dam days a winter
Moderate risk. On an ordinary house in Norwich, conditions for an ice dam come on about 7.5 days in a normal winter, mostly in January and February.
Norwich averages 28 inches of snow a year and about 30 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 Norwich
| Attic | Dam days | Risk |
|---|---|---|
| Air-sealed and well insulated | 5.3 | Moderate |
| Typical, some insulation, not air-sealed | 7.5 | Moderate |
| Older or poorly insulated, warm attic | 10.3 | Moderate |
Sealing and insulating a typical attic takes out about 2.2 days a winter here. It does not move the risk band, but it shortens every dam.
Preventing ice dams on a Norwich 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.
Which to spend on first: air sealing or heat cable.
Norwich winter, month by month
| Month | Snow (in) | Days on ground | Dam days |
|---|---|---|---|
| January | 9.0 | 9.9 | 2.9 |
| February | 7.1 | 9.8 | 2.5 |
| March | 5.0 | 4.3 | 0.8 |
| April | 0.8 | 0.3 | 0.0 |
| November | 0.3 | 0.4 | 0.1 |
| December | 5.6 | 5.5 | 1.3 |
Norwich next to nearby towns
Norwich ranks 12 of 21 Connecticut cities here for ice-dam days, behind Torrington at 23.6 days.
- New London, CT 15 mi, 4.8 days
- Groton, CT 15 mi, 4.8 days
- Middletown, CT 29 mi, 11.7 days
- Hartford, CT 34 mi, 11.2 days
- Cranston, RI 35 mi, 6.0 days
Where these numbers come from
NOAA 1991–2020 climate normals from Norwich Public Utility Plt, 1.9 miles from Norwich. 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.