City points to problematic roof structure as culprit in latest Anchorage collapse

An Anchorage building official blamed a familiar problem as the likely cause of the third commercial building roof to collapse in the city this winter.

The roof that buckled early Monday, at a warehouse at 7920 Schoon Street in the Taku-Campbell Lake area, involved the same wooden roof frames that are believed to have contributed to most of the 19 collapses that have occurred this winter and last, said Ross Noffsinger, acting building official for the municipality of Anchorage.

Those frames support flat roofs built before 1990. They typically span large open, areas, such as over warehouses. Beams in the framework, or trusses, are connected with metal gang plates that are often inadequately sized or placed.

As a result, the failed roofs have not been able to meet Anchorage code that typically requires that buildings support a minimum of 40 pounds per square foot.

“Portions of the structure were occupied at the time of the collapse,” but there were no injuries in the incident, the Anchorage Fire Department said in a statement Monday evening emailed by public information officer Lexi Qass’uq Trainer.

[Should you shovel your roof? A Q&A with an Anchorage building official]

“Wind loading and ice damming can cause these loads to be heavier so each roof should be evaluated individually for its specific condition and load,” the statement said. “A structural engineer is the best person to conduct a building evaluation and determine risk and or safety.”

The collapse shows some buildings are “not performing to code standard as designed,” said Alex Boyd, assistant fire chief with the department.

Noffsinger said those wooden, parallel-chord roof trusses, as they’re called, were believed to be factors in the collapse of a Spenard Builders Supply building in December.

The collapse of a roof of a vacant, condemned warehouse in Midtown, also in December, did not have the poor truss design, but the building was “grossly underbuilt” starting in the 1950s, he said.

[From 2023: Anchorage’s reported roof failures rise to at least 16 under heavy snow and ice]

But the poor truss design once again appears to be the problem in Monday’s collapse, he said.

Also, the trusses spanned 80 feet from bearing wall to bearing wall, so they bore a large amount of snow load.

“That’s a big span,” he said. “A lot of failures we saw last year were 30 feet or more.”

Noffsinger said a small building adjacent to the damaged warehouse, apparently an office space for Ace Delivery, did not collapse, explaining why people were able to leave that area unharmed.

That building was much smaller in size, with a smaller roof, he said. Interior walls that can support snow loads, even if they’re not designed to, could have helped prevent that building from collapsing, he said. A smaller span for those trusses may also have helped, he said.

Ace Delivery and Moving is located at the address, state records show. The owner of the business could not be reached on Tuesday, and calls to the business since the collapse have not gone through.

Jerrod Vaughn, co-owner of the warehouse building just to the north of the collapsed building, said he was in the office of his HVAC supply company when he heard the neighboring roof collapse, sometime around 10:40 a.m. or so.

It sounded like a freight train, he said.

“I thought it was an earthquake at first, but it was definitely not an earthquake,” he said.

He checked on his employees and employees from the collapsed building who’d gathered outside, and made sure all were safe, he said.

“The moral of the story is people need to shovel flat roofs in Anchorage,” he said. “The storm (on Sunday) might have just added enough weight.”

Vaughn said his business shares a wall with Ace Delivery and Moving. He said his unit is being evaluated to make sure it’s safe.

Anchorage resident Lisa Switzer on Monday evening shared a security video of the collapse taken from a neighboring building on social media. “Oh my God,” a person says in the video, as the building buckles.

The municipality early this winter issued guidance on the truss design and those older commercial buildings, encouraging building owners to clear snow from those roofs.

Heavy snowfalls in November and December have created a large snow load for roofs early in the season, expanding the time for a roof to fail, Noffsinger said.

Roofs currently are holding about 25 pounds of snow load, based on physical measurements by an engineering firm of more than 30 structures around Anchorage, he said.

“We’re still seeing failures with this type of truss design at around 25 pounds of snow load, so that’s the big takeaway from this,” he said.

The roof of the warehouse that collapsed Monday appeared to not have been shoveled at all this winter, based on the accumulated snow and the fact that the entire warehouse roof came down, Noffsinger said.

“But mind you, these buildings should not be failing with 25 pounds of snow on the roof, or 30 pounds, whatever was there,” he said.

Scott Hamel, dean of the civil engineering department at the University of Alaska Anchorage, said the physical measurements of the snow include moisture content. The city got a lot of heavy, moist snow early in the season, he said.

“We measure the weight of the snow,” he said. “The weight encompasses both depth and moisture content.”

As for houses, Hamel said homes with pitched roofs should be fine at this point if those roofs haven’t been shoveled.

A flat-roof house, however, may require a closer look to make sure it has adequate roof framework. It’s important to make sure there’s no ice damming that can contribute to heavy weight buildup in small areas or other problems like leaking roofs.

Noffsinger said homeowners should start thinking about shoveling their roofs soon, especially if snow continues to fall at the same rate this winter.

He said the municipality on Monday encouraged building owners near the collapsed roof at 7920 Schoon to shovel their roofs, since many structures in the area appear to be similarly built at the same time, in the 1980s.

On Tuesday, shovelers pushed snow off a handful of nearby roofs.

Noffsinger said it will likely be a long time before the building can be repaired.

“At this point, it’s a code abatement case for the municipality, it will take a building permit to repair the building, generally these take a long time to run through the insurance company,” he said.

He said the municipality is creating a database of buildings in Anchorage with the problematic roof designs, in order to encourage property owners to clear the roofs.

If the snow continues to fall in large amounts this winter, the municipality will try to expand the reach of its guidance.

“The guidance will be more broad, and we’ll be more vocal about homeowners shoveling their roofs,” he said.