Ice dam risk in Greenfield, WI
Ice dams in Greenfield, WI: how often
18.9 dam days a winter
High risk. On an ordinary house in Greenfield, conditions for an ice dam come on about 18.9 days in a normal winter, mostly in January and February.
Greenfield averages 52 inches of snow a year and about 60 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 Greenfield
| Attic | Dam days | Risk |
|---|---|---|
| Air-sealed and well insulated | 9.6 | Moderate |
| Typical, some insulation, not air-sealed | 18.9 | High |
| Older or poorly insulated, warm attic | 30.6 | High |
Sealing and insulating a typical attic takes out about 9.3 days a winter here. It drops the risk from high to moderate. An older house with a warm attic should expect closer to 30.6 days.
Preventing ice dams on a Greenfield 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.
Greenfield winter, month by month
| Month | Snow (in) | Days on ground | Dam days |
|---|---|---|---|
| January | 13.5 | 18.5 | 6.8 |
| February | 13.6 | 18.2 | 5.8 |
| March | 8.3 | 8.0 | 1.7 |
| April | 2.1 | 0.8 | 0.1 |
| October | 0.1 | 0.0 | 0.0 |
| November | 1.4 | 0.5 | 0.1 |
| December | 13.3 | 13.6 | 4.5 |
Greenfield next to nearby towns
Greenfield ranks 81 of 98 Wisconsin cities here for ice-dam days, behind Wausau at 41.6 days.
- Greendale, WI 1 mi, 18.4 days
- West Allis, WI 3 mi, 18.9 days
- Franklin, WI 5 mi, 18.4 days
- New Berlin, WI 6 mi, 21.4 days
- Cudahy, WI 7 mi, 18.4 days
Where these numbers come from
NOAA 1991–2020 climate normals from West Allis, 3.9 miles from Greenfield. 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.