Preventing roof collapse and damage from ice

Most pitched roofs in our area are built to withstand the weight of snow common in the Pacific Northwest. The biggest concern about roof collapse during heavy snow is for flat roofs. The KOMO story below includes an interview with Bothell Building Official David Swasey. Take a look!

Some signs of roof stress due to heavy snow or ice

  • Sagging ceiling tiles or boards, ceiling boards falling out of the ceiling grid, and/or sagging sprinkler lines and sprinkler heads
  • Sprinkler heads deflecting below suspended ceilings
  • Popping, cracking, and creaking noises
  • Sagging roof members, including metal decking or plywood sheathing
  • Bowing truss bottom chords or web members
  • Doors and/or windows that can no longer be opened or closed
  • Cracked or split wood members
  • Cracks in walls or masonry
  • Severe roof leaks
  • Excessive accumulation of water at nondrainage locations on low slope roofs

What to do?

  • Your safety is more important than any property. Consider hiring a roofing contractor for help.
  • If you think your roof or deck is overstressed, keep out of or off of the structure. Do not add your weight to overstressed roofs or decks in an attempt to clear it. 
  • As snow begins to melt, it’s important to ensure rooftop drains and downspouts are functioning and clear of ice or other obstructions.
  • If you choose to remove snow from your rooftop, please apply best practices for safe removal.
  • If you experience damage to your property and feel concerned for your safety, leave the premises and call 9-1-1. First responders will coordinate with our structural inspectors to evaluate whether a structure may remain occupied if damaged.  

Roof damming

When temperatures rise (during the day), the snow melts and starts to reach roof edges/gutters. As temperatures drop (at night) this water then freezes, becoming trapped at the eave areas. This is called ice damming and can add more weight to a roof. If left for a long period, this ice/moisture can get under shingles at the roof edges and possibly damage roof sheathing underneath. This ice build up should be removed, if there is a safe way to do so.

Immediate action for roof damming

  • Remove snow from the roof, only if you can do so safely. This eliminates one of the ingredients necessary for the formation of an ice dam. A "roof rake" and push broom can be used to remove snow, but may damage the roofing materials.
  • In an emergency situation where water is flowing into the house structure, making channels through the ice dam allows the water behind the dam to drain off the roof. Hosing with tap water on a warm day will do this job. Work upward from the lower edge of the dam. The channel will become ineffective within days and is only a temporary solution to ice dam damage.

Long-term action to prevent roof damming

  • First, make the ceiling air tight so no warm, moist air can flow from the house into the attic space.
  • After sealing air leakage paths between the house and attic space, consider increasing the ceiling/roof insulation to cut down on heat loss by conduction.

Source for roof damming, and for more information, University of Minnesota Extension.