Snow Accumulation and Your Roof

When winter storms hit the Lower Mainland, commercial and residential roofs bear the brunt of active weather systems. With all this snow sticking around, how does a homeowner know when to do something or just let it melt? Snow piled up on a roof isn’t necessarily a bad thing. Here are some facts about snow accumulation and your roof that will help you decide if you should take action.

Snow on the roof is a good sign.

If snow lands on the roof but doesn’t stay or accumulates in some areas but melts in others, it is most likely due to heat escaping from the attic. The cycle of melting-freezing-melting typically results in the formation of ice dams, which can cause serious problems for both the roof and the gutters. Snow on the roof is a good sign that your home is not experiencing heat loss through the attic.

Snow can weigh a roof down.

It might look like it’s light and fluffy while it’s falling from the sky. But once it lands on a roof, depending on what type of snow it is, accumulated snowflakes can weigh a roof down. Wet snow weighs heavier than dry snow. It’s important to know what type of snow has fallen – follow local weather forecasts for detailed information that will help you decide if your roof is in any danger of collapsing. Keep in mind, most roofs are capable of holding up to 40” of new snow before they become stressed.

How much snow is too much?

If you are concerned or unsure about whether or not your roof can handle the weight of accumulated snow, there are websites that offer snow load calculations and tables. Factors including the kind of snow, how much has fallen, and the pitch of the roof (low-slope or steep) need to be considered in order to determine how much snow is too much.

Depending on circumstances such as microclimate, the age of the house, and how old the roof is, the general rule of thumb is a residential roof might be in danger of collapse if the snow load accumulation is over 25 pounds per square foot. Most roofs in the lower mainland can easily handle unexpected amounts of snowfall; it’s only under extreme snowfall conditions that roofs can collapse under the weight.

Remove accumulated snow only if you have to.

Many roofing professionals agree that unless the snow is causing problems, it should be left to melt. Consider having snow removed from the roof when:

  • Vents have been covered by the snow
  • Cracks appear and/or rafters start to bend in the attic
  • Your home is prone to ice dams
  • The house is older and the roof has never been replaced
  • New cracks appear in drywall or plaster especially around door frames
  • Sections of the roof sag