Ice dam risk in Lawrence, MA
Ice dams in Lawrence, MA: how often
20.5 dam days a winter
High risk. On an ordinary house in Lawrence, conditions for an ice dam come on about 20.5 days in a normal winter, mostly in January and February.
Lawrence averages 58 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 Lawrence
| Attic | Dam days | Risk |
|---|---|---|
| Air-sealed and well insulated | 13.4 | Moderate |
| Typical, some insulation, not air-sealed | 20.5 | High |
| Older or poorly insulated, warm attic | 29.5 | High |
Sealing and insulating a typical attic takes out about 7.2 days a winter here. It drops the risk from high to moderate. An older house with a warm attic should expect closer to 29.5 days.
What to do about ice dams in Lawrence
- 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.
Lawrence winter, month by month
| Month | Snow (in) | Days on ground | Dam days |
|---|---|---|---|
| January | 16.2 | 21.4 | 7.0 |
| February | 15.6 | 20.7 | 6.3 |
| March | 11.9 | 16.2 | 3.5 |
| April | 1.8 | 2.0 | 0.2 |
| October | 0.1 | 0.2 | 0.0 |
| November | 1.4 | 1.8 | 0.3 |
| December | 10.8 | 12.3 | 3.2 |
Lawrence next to nearby towns
Lawrence ranks 8 of 58 Massachusetts cities here for ice-dam days, behind Pittsfield at 31.3 days.
- Methuen, MA 3 mi, 20.5 days
- Haverhill, MA 7 mi, 20.5 days
- Lowell, MA 9 mi, 18.8 days
- Woburn, MA 15 mi, 16.8 days
- Amesbury, MA 15 mi, 20.5 days
Where these numbers come from
NOAA 1991–2020 climate normals from Haverhill, 6.6 miles from Lawrence. 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.
- Snow-on-the-ground counts come from a second, nearby station, because the closest one does not record them.