Tahoe boom: Repairing snow damage | nnbw.com

Tahoe boom: Repairing snow damage

Rob Sabo

Engineering and construction firms are scrambling to repair the damage to buildings caused by massive accumulation of snow in the Lake Tahoe Basin last winter.

Jared Krupa, principal engineer for K2 Engineering and Structural Design of Reno, has taken on repair work for a half-dozen structures in and around Lake Tahoe that were damaged by the weight of snowfall. In many cases, Krupa says, buildings were three or more decades old and were not built to today’s standards.

However, Paul Laudenschlager, chief executive officer of Alpen Engineering of Truckee, says one of the structures he’s repairing is just three years old. Though it was built properly, its roof was not engineered to withstand the weight of more than a dozen feet of snow, and a section of the roof ripped away from the main house under heavy snow.

Areas of failure, he says, typically include deck ledgers that tear away from buildings, or lower roofs that become detached under the extreme weight of water-laden snow building up over time.

“There have been some failures with code-conforming buildings on Echo Summit,” Laudenschlager says. “Some of the failures were caused by inadequate engineering or construction. Others were caused by the snow situation itself and the failure of the engineer to take into account the actual situation with the building.”

Laudenschlager says some problems arise when engineers fail to consider lateral snow issues, which may exceed seismic and wind requirements. Walls can inadvertently act as a retaining wall for wind-driven snow, and many caved in this winter, particularly on Echo Summit in eastern El Dorado County.

“It is the issue most overlooked on the summit,” he says.

The snowpack in the region peaked on March 28, says the California Department of Water Resources. At Echo Summit the snowpack was 13.7 feet, in Heavenly Valley it was 11.8 feet deep, and at Mt. Rose it was 14.8 feet deep.

The problem isn’t with county building code requirements which are more than sufficient, engineers say. Rather, older structures that were under-engineered or haphazardly built can’t stand up to the mountains of snow that accumulated last winter.

Krupa says engineers typically take into account snow accumulation, and also calculate snow duration for about a month. However, problems began cropping up last winter as storm after storm pounded the region, and snow stayed on structures for months.

Early-year snow in the Sierra typically is lighter and fluffier and contains between 20 and 25 percent water density, says Andy Reising, snow surveys specialist with the California Department of Water Resources. Snow at 25 percent, Reising says, weighs 15.6 pounds per cubic foot. When the snow begins to melt as it did during the dry January month, snow compacts and can reach densities of 50 to 60 percent.

Snow with 50 percent density weighs 31.2 pounds per cubic foot. A foot of snow covering a 2,000 square-foot roof can add 62,400 pounds of weight across the structural roofing members.

“There is no substitute for complete and thorough engineering and complete and thorough construction,” Laudenschlager says. “Those are the things that came to haunt people in big winters like this. Buildings that are adequately constructed have had no trouble.”

The way a building is located on a plot of land also greatly affects how it reacts to heavy snowloads.

Don Jeppson, a licensed architect and director of the Washoe County Department of Building and Safety, says many of the structures that failed this winter were located deep in the trees with north-facing roofs that saw little sun to melt the accumulated snow. Jeppson says several patio covers on the upper elevations of Mt. Rose Highway also failed, but those were un-permitted structures.

“Washoe County has been pretty strict about snow and wind loads on carports” Jeppson says. “The city has experienced quite a few apartment complex carports failing, and Reno and Sparks have beefed up codes for those types of structures.”

Despite the number of structure failures in the region, Jeppson says current building codes are sufficient to meet even the nastiest winter.

“Building codes have been strengthened over the last couple of code cycles, and I hesitate to think we need any more restrictions or increases on snow loads. The engineers that design these systems can always design them to be more beefy and strong.”

And therein lies the main cause of friction in the decades-old debate between builders and engineers, says K2’s Krupa. Animosity can arise between the two groups when engineers choose to make everything heavier and stiffer, and 30-year builders who have never had their work fail bear the onus of erecting a more difficult and time-consuming building.

Repair work typically doesn’t need to be re-permitted, Krupa says, so long as it is built the way it was before it failed. However, he notes, the insurance companies that are footing the bill for repairs this summer want assurances the structure won’t fail again if re-built to original building plans.

“We come out and analyze what was there before and assess why it came down,” Krupa says. “Almost always it is a case where the structure wasn’t engineered correctly, or (rafter or joist) members were over-spanned.”

The work comes as a blessing for engineers and construction firms, who have struggled to keep key employees busy during the extensive construction downturn in Greater Reno-Tahoe. Krupa says K2 Engineering normally wouldn’t take on such small-scale design work, but in today’s economy the firm happily engages in a variety of work.

“In the old days work came in faster than we could do it, and now we have to go out and shake trees. This is the kind of stuff that falls out of the tree when you shake it,” he says.