Anchorage officials warn owners of some commercial buildings to clear snow from roofs

The Municipality of Anchorage issued guidance this week advising some commercial property owners to clear snow off their roofs after above-average accumulation this month.

The risk is roof failure or total collapse. Last year, which also saw heavier-than-normal levels of snow atop buildings, at least 16 roofs were damaged in partial or full failures.

“Anchorage has received an exceptional amount of snow with an exceptionally high moisture content,” according to a snow removal notice put out by the city’s Development Services department. “We estimate that typical roof snow loads in Anchorage are already at 30% to 60% of the total design snow load of 40 pounds per square foot, depending on location, melting, etc.”

Of particular concern are commercial buildings constructed before 1990 with certain designs of wooden trusses supporting broad roofs.

“Top chord bearing parallel cord trusses demand extra attention due to a potential design flaw that can result in a cross-grain tension (shear) type of failure in the top chord near the bearing point,” the municipality’s notice said. “Bottom chord bearing trusses have also failed, including a pitched-roof type of truss.”

When it comes to clearing snow loads, time matters. According to the department, the longer that building materials are stressed, the more likely they are to fail.

In February, a woman was killed and two others temporarily trapped when the roof of a South Anchorage gym collapsed. None of the incidents at other businesses involved reports of injuries.

Given the number of structures affected and limited number of qualified professionals to clear roofs, municipal officials are asking contractors to prioritize working on buildings that meet the criteria outlined in the city’s guidance materials.

And they said that with winter only just beginning, snow is likely to keep piling up.

“Given our weather seems to follow patterns, it is likely we will continue to see above average precipitation this winter,” the city’s notice said. “We should expect the roof snow to continue to accumulate.”

More guidance is available through the Building Services Department.