Ice dam risk in Lowell, MA
How often ice dams form in Lowell
18.8 dam days a winter
High risk. On an ordinary house in Lowell, conditions for an ice dam come on about 18.8 days in a normal winter, mostly in January and February.
Lowell averages 59 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 Lowell
| Attic | Dam days | Risk |
|---|---|---|
| Air-sealed and well insulated | 12.0 | Moderate |
| Typical, some insulation, not air-sealed | 18.8 | High |
| Older or poorly insulated, warm attic | 27.2 | High |
Sealing and insulating a typical attic takes out about 6.7 days a winter here. It drops the risk from high to moderate. An older house with a warm attic should expect closer to 27.2 days.
What to do about ice dams in Lowell
- 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.
Lowell winter, month by month
| Month | Snow (in) | Days on ground | Dam days |
|---|---|---|---|
| January | 16.1 | 20.2 | 6.6 |
| February | 12.5 | 18.8 | 5.6 |
| March | 12.9 | 13.2 | 2.9 |
| April | 2.3 | 1.2 | 0.1 |
| October | 0.1 | 0.0 | 0.0 |
| November | 1.9 | 1.7 | 0.3 |
| December | 13.2 | 12.5 | 3.3 |
Lowell next to nearby towns
Lowell ranks 13 of 58 Massachusetts cities here for ice-dam days, behind Pittsfield at 31.3 days.
- Lawrence, MA 9 mi, 20.5 days
- Methuen, MA 10 mi, 20.5 days
- Nashua, NH 11 mi, 24.1 days
- Woburn, MA 13 mi, 16.8 days
- Haverhill, MA 15 mi, 20.5 days
Where these numbers come from
NOAA 1991–2020 climate normals from Bedford, 10.9 miles from Lowell. 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.