Ice dam risk in London, OH
Will your roof get ice dams in London, OH?
10.4 dam days a winter
Moderate risk. On an ordinary house in London, conditions for an ice dam come on about 10.4 days in a normal winter, mostly in January and February.
London averages 24 inches of snow a year and about 38 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 London
| Attic | Dam days | Risk |
|---|---|---|
| Air-sealed and well insulated | 5.7 | Moderate |
| Typical, some insulation, not air-sealed | 10.4 | Moderate |
| Older or poorly insulated, warm attic | 16.2 | High |
Sealing and insulating a typical attic takes out about 4.7 days a winter here. It does not move the risk band, but it shortens every dam. An older house with a warm attic should expect closer to 16.2 days.
Preventing ice dams on a London 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.
Which to spend on first: air sealing or heat cable.
London winter, month by month
| Month | Snow (in) | Days on ground | Dam days |
|---|---|---|---|
| January | 7.0 | 14.0 | 4.4 |
| February | 6.6 | 11.8 | 3.3 |
| March | 4.1 | 3.9 | 0.7 |
| April | 0.1 | 0.0 | 0.0 |
| November | 0.7 | 0.5 | 0.1 |
| December | 5.5 | 7.5 | 1.9 |
London next to nearby towns
London ranks 97 of 176 Ohio cities here for ice-dam days, behind Euclid at 24.8 days.
- Hilliard, OH 18 mi, 10.4 days
- Springfield, OH 19 mi, 7.8 days
- Grove City, OH 20 mi, 6.7 days
- Upper Arlington, OH 22 mi, 6.6 days
- Dublin, OH 22 mi, 10.4 days
Where these numbers come from
NOAA 1991–2020 climate normals from Marysville, 22.7 miles from London. 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.