Ice dam risk in Spencer, IA
Will your roof get ice dams in Spencer, IA?
27.3 dam days a winter
High risk. On an ordinary house in Spencer, conditions for an ice dam come on about 27.3 days in a normal winter, mostly in January and February.
Spencer averages 43 inches of snow a year and about 76 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 Spencer
| Attic | Dam days | Risk |
|---|---|---|
| Air-sealed and well insulated | 11.7 | Moderate |
| Typical, some insulation, not air-sealed | 27.3 | High |
| Older or poorly insulated, warm attic | 46.8 | Severe |
Sealing and insulating a typical attic takes out about 15.6 days a winter here. It drops the risk from high to moderate. An older house with a warm attic should expect closer to 46.8 days.
What to do about ice dams in Spencer
- 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.
Spencer winter, month by month
| Month | Snow (in) | Days on ground | Dam days |
|---|---|---|---|
| January | 9.8 | 22.3 | 9.4 |
| February | 8.9 | 19.1 | 7.3 |
| March | 5.9 | 9.3 | 2.4 |
| April | 3.0 | 1.7 | 0.2 |
| May | 0.1 | 0.0 | 0.0 |
| October | 0.7 | 0.2 | 0.0 |
| November | 5.3 | 5.5 | 1.4 |
| December | 9.6 | 17.4 | 6.6 |
Spencer next to nearby towns
Spencer ranks 3 of 41 Iowa cities here for ice-dam days, behind Mason City at 28.7 days.
- Storm Lake, IA 35 mi, 27.7 days
- Worthington, MN 40 mi, 34.3 days
- Fairmont, MN 49 mi, 30.3 days
- Le Mars, IA 57 mi, 24.4 days
- Fort Dodge, IA 66 mi, 24.4 days
Where these numbers come from
NOAA 1991–2020 climate normals from Spencer 1 N, 1.3 miles from Spencer. 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.