A good rule of thumb is to get your roof cleared after every 6 inches of snowfall. If you prevent too much snow from piling up on your roof, it’s much harder for ice dams to form and you can certainly stop worrying about any sort of roof cave-in.
Of course, it all depends: I’ve seen ice dams form with only a dusting of snow on the roof. I’ve also seen roofs with mountains of snow remain free of ice dams.
Generally speaking, even though every roof is different, you’ll especially want to consider this “6-inch” rule of thumb if you’ve repeatedly had problems with ice dams in the past.
On the other hand, if you’ve never had an ice dam and your only concern is avoiding a roof collapse, then you might want to consider holding off on any roof snow removal until you’ve accumulated a foot or more of snow.
When deciding the right time to get roof snow removal, it’s also important to take into account how heavy the snow is. Wet, heavy snow can weigh 6 or more times as much as lighter dryer snow. One cubic foot of snow can typically range in weight from as little as 0.26lbs (light, dry snow) to as much as 1.66lbs. (heavy, wet snow). If you step outside and pick up the snow and it seems heavy and wet, that’s one factor that might indicate you should get your roof cleared sooner rather than later.
How often you need to get your roof cleared also depends partly on the weather forecast.
If 6 inches of snow falls on your roof but the nighttime and daytime low temperatures are forecast to stay above freezing for a couple of days, you probably don’t need to get the snow removed—because it will likely melt soon enough (or at least decrease significantly in weight) and never become an ice dam.
However, if 6 inches of snow falls one night and another 6 inches of snowfall is forecast for later in the week, or if the low temperatures remain below freezing, you may want to remove the snow ASAP. Or better yet, call a roof snow removal service right away and schedule your roof snow removal in advance – for shortly after the second storm is forecast to arrive. This way, you’ll get both snowfalls removed from your roof with one phone call, and you’ll be first in line during a particularly busy time for local roof snow removal companies.