Anchorage officials say up to 1,000 commercial buildings at risk of roof collapse, and urge homeowners to clear snow too

Building officials in Anchorage have issued new guidance to residential and commercial building owners advising them to clear heavy snow loads from roofs, adding another measure of urgency for residents during a winter that’s already seen at least three structures collapse.

Last year, which saw similarly heavy snow accumulate in the municipality, 16 roofs failed, causing full or partial building collapses, and killing one resident.

The buildings at the highest risk are commercial structures with large roofs built prior to 1990 and supported by wooden trusses with metal gang nail plates. According to the statement from the municipality’s Development Services, all but one of the roofs built with such techniques that collapsed last winter buckled under snow loads significantly less heavy than the 40 pounds of weight per square foot they are designed to withstand.

“We estimate there (are) between 500 and 1,000 buildings in Anchorage that have the roof trusses of immediate concern,” officials wrote in their latest guidance on snow removal.

It was an exceptionally snowy start to the winter in Southcentral Alaska, and additional accumulation is all but certain in the remaining months of winter.

“We estimate that typical roof snow loads in Anchorage are at 50% to 80% of the total design snow load of 40 pounds per square foot, depending on location, melting,” officials wrote. “Time matters. When subjecting wood construction to large loads, duration matters. The longer wood is subjected to extreme stress, the greater the chance of failure.”

It is the second time the municipality has issued such guidance. The difference this time is that they are now encouraging residential homeowners to clear off snow, too.

“Given how early it is in the season, people should consider removing the snow to reduce the weight on the structure,” officials wrote.

So far there are no reports of any major structural failures at homes or apartment buildings. But inspectors are seeing unsettling data.

“We have received confirmed reports of snow loads of over 30 pounds per square foot, and there could be areas of town that have a higher snow load. That is a lot of weight,” they wrote, pointing out that that level of snow on a 1,500-square-foot roof would be the equivalent of loading it with “about 8 full size light duty pickup trucks.”

They advise that anyone who spots signs of distress affecting their home should begin clearing snow as soon as possible. According to the city’s notice, such signs include:

• “Sagging roof: Noticeable sagging in the roof is a clear sign the weight of the snow is too much for the structure to bear.”

• ”Strange noises: Sounds like creaking, popping, or cracking coming from the roof or attic area can indicate the roof is under stress from the snow’s weight.”

• “Doors and windows that used to open freely stick or jam: If interior doors or windows begin to stick or can’t be opened easily, it may be a sign that the weight of snow is deforming the structure of the house.”

• “Ice dams: Ice dams forming at the edge of the roof can create a heavy load on the eaves and lead to water damage as snow melt on the roof finds its way into the structure.”

More information and guidance can be found through the municipality’s Development Services website.