Ten inches of fresh snow equates to about five pounds per square foot, which means your roof likely can support four feet of fresh snow. Packed snow, however, weighs more: two feet or more of old snow is enough to exceed weight limits.

How Much Weight Can a Roof Hold?

Roofs can hold quite a bit of weight — and that’s good news for us. However, even with this in mind, your roof’s ability to withstand weight is bound to fluctuate based on factors such as the age of your roof as well as how well your roof has been maintained.

In general, the average home roof can hold around 20 pounds per square foot of roofing. Although this may seem to be a good match for withstanding snow on the surface, there’s a reason why local building codes often dictate a removal strategy for snow on roofs. In Vancouver, for example, it is required by local building code that your roof must be certified to hold 25 pounds per square foot.

It is also worth noting that there are other factors that can affect how well your roof holds snow, such as your roof’s degree of slope, shape, and materials. While a sloped roof may do a decent job of draining precipitation off the side of a roof, flat roofs or roofs with very minor sloping may be more susceptible to heavy snow accumulation.

At what point should you remove the snow from your roof?

The first decision you should make is when to remove the snow—no need to spend any more time or money than necessary. So, how can you tell when there’s too much snow or ice dams are forming? Consider these questions:

• Is your roof shallow or flat? These types of roofs are more likely to suffer structural damage or collapse from snow because the snow tends to accumulate faster. Because of the lack of slope, water will accumulate, even as the snow melts, which will refreeze, causing ice dams. So, this type of roof will need to be cleared sooner that a higher pitched roof.
• How wet is the snow? The density of the snow makes a big difference in the weight. Fluffy, dry snow does not weigh as much as wet snow or older snow that has accumulated. You can also end up with old layers of snow that have melted and then frozen, causing even more weight. 
• Are there snow drifts or is the snow distributed unevenly on your roof? Snow does not usually spread itself out evenly over the surface of your roof as it’s falling, and therefore is likely to accumulate unevenly. In addition, the wind can move snow, creating snow drifts. The heaviest accumulation is often where slopes or exterior walls come together.
• How do you check for snow overload? One way to do this is by opening your doors and windows, one at a time.If they do not easily open or feel like they are stuck, your roof probably is bearing too much weight from the snow.

Different regions typically produce different types of snow. Western regions often produce lighter, fluffy snow (that powder skiers and snowboarders rave about), whereas Eastern regions often accumulate heavier snow. Even within regions different snow type accumulate: Boston snow may be different than Worcester snow.