Ice dam risk in Juneau, AK
Will your roof get ice dams in Juneau, AK?
16.3 dam days a winter
High risk. On an ordinary house in Juneau, conditions for an ice dam come on about 16.3 days in a normal winter, mostly in January and February.
Juneau averages 88 inches of snow a year and about 68 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 Juneau
| Attic | Dam days | Risk |
|---|---|---|
| Air-sealed and well insulated | 9.0 | Moderate |
| Typical, some insulation, not air-sealed | 16.3 | High |
| Older or poorly insulated, warm attic | 25.3 | High |
Sealing and insulating a typical attic takes out about 7.3 days a winter here. It drops the risk from high to moderate. An older house with a warm attic should expect closer to 25.3 days.
What to do about ice dams in Juneau
- 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.
Juneau winter, month by month
| Month | Snow (in) | Days on ground | Dam days |
|---|---|---|---|
| January | 24.5 | 17.6 | 4.9 |
| February | 16.7 | 15.2 | 3.8 |
| March | 12.4 | 12.7 | 2.7 |
| April | 1.2 | 0.9 | 0.1 |
| October | 0.9 | 0.4 | 0.0 |
| November | 13.8 | 7.1 | 1.3 |
| December | 18.1 | 13.6 | 3.4 |
Juneau next to nearby towns
Juneau ranks 4 of 4 Alaska cities here for ice-dam days, behind Fairbanks at 80.6 days.
- Anchorage, AK 558 mi, 57.6 days
- Wasilla, AK 571 mi, 43.5 days
- Fairbanks, AK 626 mi, 80.6 days
- Lynden, WA 806 mi, 0.6 days
- Ferndale, WA 809 mi, 0.2 days
Where these numbers come from
NOAA 1991–2020 climate normals from Juneau Airport, 13.7 miles from Juneau. 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.