Ice dam risk in Biddeford, ME
How often ice dams form in Biddeford
22.6 dam days a winter
High risk. On an ordinary house in Biddeford, conditions for an ice dam come on about 22.6 days in a normal winter, mostly in January and February.
Biddeford averages 49 inches of snow a year and about 75 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 Biddeford
| Attic | Dam days | Risk |
|---|---|---|
| Air-sealed and well insulated | 13.2 | Moderate |
| Typical, some insulation, not air-sealed | 22.6 | High |
| Older or poorly insulated, warm attic | 34.4 | High |
Sealing and insulating a typical attic takes out about 9.5 days a winter here. It drops the risk from high to moderate. An older house with a warm attic should expect closer to 34.4 days.
Preventing ice dams on a Biddeford 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.
Which to spend on first: air sealing or heat cable.
Biddeford winter, month by month
| Month | Snow (in) | Days on ground | Dam days |
|---|---|---|---|
| January | 13.3 | 21.7 | 7.7 |
| February | 13.3 | 21.7 | 7.2 |
| March | 9.8 | 16.3 | 4.0 |
| April | 1.3 | 2.4 | 0.3 |
| October | 0.1 | 0.1 | 0.0 |
| November | 0.7 | 1.2 | 0.2 |
| December | 10.4 | 11.1 | 3.1 |
Biddeford next to nearby towns
Biddeford ranks 7 of 11 Maine cities here for ice-dam days, behind Waterville at 40.9 days.
- Saco, ME 6 mi, 22.4 days
- South Portland, ME 14 mi, 22.4 days
- Portland, ME 17 mi, 22.4 days
- Sanford, ME 18 mi, 29.0 days
- Westbrook, ME 19 mi, 22.4 days
Where these numbers come from
NOAA 1991–2020 climate normals from Kennebunkport, 6.6 miles from Biddeford. 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.