Ice dam risk in Alpena, MI
Will your roof get ice dams in Alpena, MI?
33.6 dam days a winter
High risk. On an ordinary house in Alpena, conditions for an ice dam come on about 33.6 days in a normal winter, mostly in January and February.
Alpena averages 59 inches of snow a year and about 95 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 Alpena
| Attic | Dam days | Risk |
|---|---|---|
| Air-sealed and well insulated | 14.2 | Moderate |
| Typical, some insulation, not air-sealed | 33.6 | High |
| Older or poorly insulated, warm attic | 57.8 | Severe |
Sealing and insulating a typical attic takes out about 19.4 days a winter here. It drops the risk from high to moderate. An older house with a warm attic should expect closer to 57.8 days.
Preventing ice dams on a Alpena 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.
Alpena winter, month by month
| Month | Snow (in) | Days on ground | Dam days |
|---|---|---|---|
| January | 15.6 | 26.4 | 10.8 |
| February | 14.4 | 25.6 | 10.2 |
| March | 6.2 | 19.7 | 5.7 |
| April | 3.5 | 2.4 | 0.3 |
| October | 0.1 | 0.0 | 0.0 |
| November | 3.0 | 3.2 | 0.6 |
| December | 16.6 | 18.1 | 6.0 |
Alpena next to nearby towns
Alpena ranks 6 of 90 Michigan cities here for ice-dam days, behind Sault Ste. Marie at 48.8 days.
- Bay City, MI 105 mi, 21.6 days
- Sault Ste. Marie, MI 107 mi, 48.8 days
- Midland, MI 107 mi, 21.6 days
- Traverse City, MI 108 mi, 35.2 days
- Cadillac, MI 113 mi, 38.5 days
Where these numbers come from
NOAA 1991–2020 climate normals from Alpena Wwtp, 1.2 miles from Alpena. 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.