Ice dam risk in Troy, MI
How often ice dams form in Troy
19.6 dam days a winter
High risk. On an ordinary house in Troy, conditions for an ice dam come on about 19.6 days in a normal winter, mostly in January and February.
Troy averages 36 inches of snow a year and about 62 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 Troy
| Attic | Dam days | Risk |
|---|---|---|
| Air-sealed and well insulated | 9.6 | Moderate |
| Typical, some insulation, not air-sealed | 19.6 | High |
| Older or poorly insulated, warm attic | 32.2 | High |
Sealing and insulating a typical attic takes out about 10.0 days a winter here. It drops the risk from high to moderate. An older house with a warm attic should expect closer to 32.2 days.
Preventing ice dams on a Troy 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.
Troy winter, month by month
| Month | Snow (in) | Days on ground | Dam days |
|---|---|---|---|
| January | 12.1 | 21.7 | 7.9 |
| February | 9.0 | 17.5 | 6.0 |
| March | 4.1 | 7.4 | 1.7 |
| April | 0.9 | 0.6 | 0.1 |
| October | 0.1 | 0.0 | 0.0 |
| November | 1.7 | 1.4 | 0.2 |
| December | 8.1 | 12.9 | 3.7 |
Troy next to nearby towns
Troy ranks 29 of 90 Michigan cities here for ice-dam days, behind Sault Ste. Marie at 48.8 days.
- Clawson, MI 3 mi, 19.6 days
- Birmingham, MI 5 mi, 19.6 days
- Royal Oak, MI 5 mi, 19.6 days
- Rochester Hills, MI 6 mi, 19.6 days
- Madison Heights, MI 6 mi, 19.6 days
Where these numbers come from
NOAA 1991–2020 climate normals from Pontiac Wwtp, 6.8 miles from Troy. 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.