Roof Raking: When to Remove Snow from Your Roof

After a big snow storm (greater than a foot), the question often asked is:  “Should I rake my roof?”  The simple answer is:  it depends.  The following should be considered when making that decision:

• The pitch or slope of the roof. Low slope and flat roofs tend to accumulate more snow.
• Valleys or intersecting roof lines. The more complex the roof design, the more areas prone to snow accumulation.
• The roof’s structural design — roofs built to modern ICC codes. Roofs built to older codes (pre-1975) may not.
• Insulation plan and theory. Gabled roofs built to modern codes are typically designed to have attic temperatures close to ambient temperatures.  Finished/warm attics may be more prone to thaw-freeze-thaw cycles, resulting in ice dams and water intrusion.
• Gutters.
• Roof composition. Roofs constructed with layers of ice and water-shield roof sheaving are less likely to suffer from water intrusion due to ice dams at the gutter line.
• Snow density.  For a 1-foot depth, snow can range from 3 lbs. per square foot up to 21 lbs. per square foot.  After a snow storm, even if temperatures are below freezing, solar radiation can melt snow, which can then refreeze overnight.  The depth of the snow may be decreasing in a freeze-thaw-freeze cycle, but the weight of the snow may not be decreasing.

A higher pitched gable roof constructed with ice and water-shield and also having a clear gutter may only require raking of snow in and around the gutter.  A low pitch, older roof may require the roof to be entirely cleared of snow.

The following are some of FEMA’s recommendations for snow removal from roofs:

• Inspect, repair, and maintain the roof before winter and snow events.
• Get repairs done by a professional.
• Watch for signs of overstress — sagging roof members, ceiling tiles or sprinkler heads; cracked or split wood members; cracks in wall or masonry; and roof leaks.
• Follow any fall protection protocols for work done on rooftops.
• Use non-metallic snow rakes.
• Keep everyone and everything a safe distance from the path of falling snow.
• Alert whoever is doing the removal if you have skylights that may be covered over.
• Do not use snow throwers or sharp devices like picks or metal shovels on roofs.
• Do not create a snow pile on the roof.
• During removal, avoid dropping snow on building exits, fire escapes, dryer vents, gas service, or other equipment.

Stay safe this winter!