Ice dam risk in Thornton, CO
Will your roof get ice dams in Thornton, CO?
7.7 dam days a winter
Moderate risk. On an ordinary house in Thornton, conditions for an ice dam come on about 7.7 days in a normal winter, mostly in December and January.
Thornton averages 45 inches of snow a year and about 35 days with snow on the ground. Plenty falls, but it tends to melt off between storms, which keeps the count lower than the snowfall suggests. That gap is why snowfall alone misleads.
What your attic does to that number in Thornton
| Attic | Dam days | Risk |
|---|---|---|
| Air-sealed and well insulated | 6.3 | Moderate |
| Typical, some insulation, not air-sealed | 7.7 | Moderate |
| Older or poorly insulated, warm attic | 9.4 | Moderate |
The attic matters less in Thornton than in colder towns: there are only 1.4 days a winter between a typical attic and a sealed one.
Preventing ice dams on a Thornton roof
- 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.
More on when a roof rake is worth it.
Thornton winter, month by month
| Month | Snow (in) | Days on ground | Dam days |
|---|---|---|---|
| January | 6.0 | 6.8 | 1.8 |
| February | 7.6 | 6.5 | 1.7 |
| March | 8.2 | 4.1 | 0.8 |
| April | 6.5 | 2.7 | 0.3 |
| May | 1.2 | 0.4 | 0.0 |
| September | 0.1 | 0.0 | 0.0 |
| October | 2.4 | 1.5 | 0.1 |
| November | 6.9 | 5.1 | 1.0 |
| December | 5.9 | 7.7 | 2.0 |
Thornton next to nearby towns
Thornton ranks 36 of 53 Colorado cities here for ice-dam days, behind Steamboat Springs at 51.0 days.
- Northglenn, CO 2 mi, 7.7 days
- Federal Heights, CO 5 mi, 7.7 days
- Broomfield, CO 6 mi, 7.7 days
- Westminster, CO 7 mi, 7.7 days
- Commerce City, CO 8 mi, 9.4 days
Where these numbers come from
NOAA 1991–2020 climate normals from Northglenn, 4.1 miles from Thornton. 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.