Ice dam risk in Fairbanks, AK
How often ice dams form in Fairbanks
80.6 dam days a winter
Severe risk. On an ordinary house in Fairbanks, conditions for an ice dam come on about 80.6 days in a normal winter, mostly in January and December.
Fairbanks averages 58 inches of snow a year and about 186 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 Fairbanks
| Attic | Dam days | Risk |
|---|---|---|
| Air-sealed and well insulated | 24.1 | High |
| Typical, some insulation, not air-sealed | 80.6 | Severe |
| Older or poorly insulated, warm attic | 151.2 | Severe |
Sealing and insulating a typical attic takes out about 56.5 days a winter here. It drops the risk from severe to high. An older house with a warm attic should expect closer to 151.2 days.
Preventing ice dams on a Fairbanks 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.
- Heat cable is worth pricing here even on a sealed house, along the eave and in the gutters and downspouts it drains into.
Running 60 feet of 5 W/ft cable whenever snow lies below freezing would use about 1,017 kWh a winter in Fairbanks, roughly $173 at 17 cents a kWh.
Which to spend on first: air sealing or heat cable.
Fairbanks winter, month by month
| Month | Snow (in) | Days on ground | Dam days |
|---|---|---|---|
| January | 8.7 | 31.0 | 15.3 |
| February | 9.6 | 28.5 | 13.4 |
| March | 6.1 | 31.0 | 12.8 |
| April | 2.8 | 20.4 | 5.2 |
| May | 0.2 | 0.6 | 0.0 |
| September | 1.3 | 0.4 | 0.0 |
| October | 5.4 | 13.7 | 4.5 |
| November | 13.2 | 29.1 | 14.3 |
| December | 10.5 | 31.0 | 15.1 |
Fairbanks next to nearby towns
Fairbanks ranks 1 of 4 Alaska cities here for ice-dam days, the worst in the state.
- Wasilla, AK 232 mi, 43.5 days
- Anchorage, AK 258 mi, 57.6 days
- Juneau, AK 626 mi, 16.3 days
- Lynden, WA 1433 mi, 0.6 days
- Ferndale, WA 1435 mi, 0.2 days
Where these numbers come from
NOAA 1991–2020 climate normals from Aurora, 2.4 miles from Fairbanks. 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.