Ice dam risk in Waterloo, IA
How often ice dams form in Waterloo
22.2 dam days a winter
High risk. On an ordinary house in Waterloo, conditions for an ice dam come on about 22.2 days in a normal winter, mostly in January and February.
Waterloo averages 39 inches of snow a year and about 64 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 Waterloo
| Attic | Dam days | Risk |
|---|---|---|
| Air-sealed and well insulated | 10.0 | Moderate |
| Typical, some insulation, not air-sealed | 22.2 | High |
| Older or poorly insulated, warm attic | 37.5 | Severe |
Sealing and insulating a typical attic takes out about 12.2 days a winter here. It drops the risk from high to moderate. An older house with a warm attic should expect closer to 37.5 days.
What to do about ice dams in Waterloo
- 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.
Waterloo winter, month by month
| Month | Snow (in) | Days on ground | Dam days |
|---|---|---|---|
| January | 10.1 | 21.4 | 8.7 |
| February | 9.3 | 18.3 | 6.6 |
| March | 4.6 | 7.6 | 1.7 |
| April | 1.7 | 0.7 | 0.1 |
| May | 0.1 | 0.0 | 0.0 |
| October | 0.3 | 0.1 | 0.0 |
| November | 3.1 | 2.9 | 0.6 |
| December | 9.9 | 13.0 | 4.5 |
Waterloo next to nearby towns
Waterloo ranks 7 of 41 Iowa cities here for ice-dam days, behind Mason City at 28.7 days.
- Cedar Falls, IA 6 mi, 22.2 days
- Waverly, IA 17 mi, 22.2 days
- Marshalltown, IA 42 mi, 20.4 days
- Marion, IA 50 mi, 18.4 days
- Cedar Rapids, IA 50 mi, 18.4 days
Where these numbers come from
NOAA 1991–2020 climate normals from Waterloo Municipal Airport, 5.0 miles from Waterloo. 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.