Ice dam risk in South Lyon, MI
Will your roof get ice dams in South Lyon, MI?
18.3 dam days a winter
High risk. On an ordinary house in South Lyon, conditions for an ice dam come on about 18.3 days in a normal winter, mostly in January and February.
South Lyon averages 61 inches of snow a year and about 59 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 South Lyon
| Attic | Dam days | Risk |
|---|---|---|
| Air-sealed and well insulated | 9.0 | Moderate |
| Typical, some insulation, not air-sealed | 18.3 | High |
| Older or poorly insulated, warm attic | 30.0 | 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 30.0 days.
What to do about ice dams in South Lyon
- 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.
South Lyon winter, month by month
| Month | Snow (in) | Days on ground | Dam days |
|---|---|---|---|
| January | 18.3 | 20.9 | 7.5 |
| February | 15.3 | 17.0 | 5.6 |
| March | 8.3 | 7.2 | 1.5 |
| April | 2.6 | 0.5 | 0.0 |
| October | 0.1 | 0.0 | 0.0 |
| November | 4.1 | 1.7 | 0.2 |
| December | 12.7 | 11.7 | 3.5 |
South Lyon next to nearby towns
South Lyon ranks 44 of 90 Michigan cities here for ice-dam days, behind Sault Ste. Marie at 48.8 days.
- Wixom, MI 8 mi, 18.1 days
- Novi, MI 9 mi, 18.1 days
- Ann Arbor, MI 13 mi, 20.5 days
- Farmington, MI 14 mi, 18.1 days
- Farmington Hills, MI 14 mi, 18.1 days
Where these numbers come from
NOAA 1991–2020 climate normals from Ann Arbor U Of Mich, 11.3 miles from South Lyon. 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.