: Heavy wet snow becomes a weighty issue for marginal structures

OKANOGAN – If there is an upside to harsher-than-usual weather events such as last months’ snowstorm it is that locals learn firsthand what additional preparation, they need to consider to be ready for the next big one.

A good example is the above-freezing temperatures that arrived with rain on the heels of the heavy snowfall. Now the issue is not the cold and wind chill but increasing snow loads resulting from the weight of more and more water. Aging structures and those with roofs not designed to shed snow quickly or not built to handle the heavy demand of deep snow plus added moisture are candidates for collapse: carports, outbuildings, and awnings.

While the weight of snow varies widely based on depth and water content tables have been calculated that give the layman some idea what those variations look like when translated into numbers. One from Cornell University estimates that two feet of dry roof snow that weighs 6.5 pounds per square foot (psf) can balloon to 42 psf when wet. Add another foot and three feet of dry roof snow at 9.5 psf becomes 62 psf of wet snow.

Okanogan County being the snow country it is requires builders to take snow load into consideration with minimum roof standards determined by geographic location. Okanogan County building inspector Dan Higbee said those requirements range from a low of 30 pounds per square foot (psf) in the valley areas like Pateros to a high of 75 psf in Mazama.

Some examples:

Brewster: 30 psf

Methow:  35 psf

Carlton:   40 psf

Conconully:  45 psf

Winthrop:   65 psf

Mazama:   75 psf

Given these minimum standards Higbee said some homeowners ramp up their roof tolerances just in case.

“We do see that quite often in the Methow,” said Higbee. “Part of the reason is the many vacation homes for people who are not there year-round. They want to make sure they are set if they cannot get over here, so they go to a higher snow load than the minimum.”

The county mandates appear to be doing their job for those who built accordingly.

“I have not heard of anything permitted and inspected having any problem,” Higbee said.

Ice buildup is another issue to consider for snow load weight variables, Higbee said.

“You have to take into account the heated buildings that do not have good insulation,” said Higbee. “They create the ice dams where the ice weighs quite a bit.”

The vulnerable structures like the Malott Improvement Club in Malott, the old Honda building near the bridge in Omak and similar sites in their category are “basically abandoned buildings with very little maintenance,” Higbee said.

While the snow accumulation so far is not unusual for places like the Methow, “I cannot recall a year where there has been this much snow in Okanogan,” Higbee said.