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.
- 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!