The more than 100 inches of snow that has fallen on Anchorage so far this winter is starting to push buildings to the breaking point.
Two roofs of commercial buildings have collapsed in the past week -- an occurrence unusual enough for the city government to issue an advisory saying that current snow loads shouldn't be a problem for most roofs in the city.
Both of the flat-roofed buildings had snow loads "well below" the 40 pounds per square foot required by municipal building codes, the city's Building Safety office said in a statement.
Design or construction problems likely contributed to the collapses, the city said.
"These roofs that collapsed probably had multiple issues going on," said Ross Noffsinger, an engineering services manager with the city.
Flat-roofed buildings, which in Anchorage tend to be mostly commercial properties, are more vulnerable to roof collapses due to snow loading, Noffsinger said.
Nevertheless, some homeowners are looking warily at their increasingly burdened roofs.
Right now, the snow at the National Weather Service offices near Ted Stevens International Airport weighs roughly 26.5 pounds per square foot, based on a snow-density calculation, said Dave Stricklan, a hydrometeorological technician with the service.
While conditions vary around the city, it would take a lot of heavy, wet snow to pass the city's 40 pound standard, he said.
Dense, wet snow tends to fall later in the winter. That's why it's important to watch for warning signs, Noffsinger said.
"A person needs to pay attention to what's going on with their roof," he said.
Factors to watch out for include snow drifts, which can add dangerous amounts of weight to an otherwise stable roof.
Excessive ice buildup, a frequent problem in older homes with poor insulation, is a worrisome sign.
Newly noticeable cracks in interior ceilings or walls also warrant a call to a structural engineer or inspector.
Flat roof drains that are ice-choked or otherwise clogged can cause a buildup of snow as well.
Pitched roofs, which make up the overwhelming majority of Anchorage homes, rarely collapse under heavy snow.
Reach Michelle Theriault Boots at email@example.com or 257-4344.