Ice dam risk in Plymouth, IN
Ice dams in Plymouth, IN: how often
15.9 dam days a winter
High risk. On an ordinary house in Plymouth, conditions for an ice dam come on about 15.9 days in a normal winter, mostly in January and February.
Plymouth averages 55 inches of snow a year and about 51 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 Plymouth
| Attic | Dam days | Risk |
|---|---|---|
| Air-sealed and well insulated | 7.7 | Moderate |
| Typical, some insulation, not air-sealed | 15.9 | High |
| Older or poorly insulated, warm attic | 26.1 | High |
Sealing and insulating a typical attic takes out about 8.2 days a winter here. It drops the risk from high to moderate. An older house with a warm attic should expect closer to 26.1 days.
Preventing ice dams on a Plymouth 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.
Plymouth winter, month by month
| Month | Snow (in) | Days on ground | Dam days |
|---|---|---|---|
| January | 18.6 | 18.8 | 6.8 |
| February | 14.1 | 14.1 | 4.5 |
| March | 6.4 | 5.0 | 1.0 |
| April | 1.1 | 0.4 | 0.0 |
| October | 0.1 | 0.0 | 0.0 |
| November | 3.3 | 1.9 | 0.3 |
| December | 11.3 | 10.6 | 3.2 |
Plymouth next to nearby towns
Plymouth ranks 1 of 88 Indiana cities here for ice-dam days, the worst in the state.
- South Bend, IN 23 mi, 15.8 days
- Mishawaka, IN 24 mi, 15.8 days
- Warsaw, IN 25 mi, 15.8 days
- La Porte, IN 27 mi, 15.5 days
- Goshen, IN 30 mi, 14.8 days
Where these numbers come from
NOAA 1991–2020 climate normals from Plymouth, 1.1 miles from Plymouth. 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.